Last updated 3-4-2022 – after release of Beta 2.7.09
Firecapture is a feature-rich astronomy program, designed by Torsten Edelmann. Its purpose is to control the operation of cameras used in high speed digital video imaging of the planets and other solar system objects.
This page attempts to help those less familiar with the program to find out how to get the most out of it, by explaining what some of the most important features do and how to set them.
Although primarily a program developed for Windows machines, Firecapture is now is available in versions for Mac, Linux, and Raspberry Pi. The information here is based on how Firecapture works on a Windows machine, as that is the only experience I have; aspects of how you use some of the features may need to be adapted by those using different operating systems.
This page is not intended to be a comprehensive user manual for Firecapture and not all features are explained. Torsten has several very good tutorials which you can find on his website. By necessity some of the screenshots shown will be of older versions of Firecapture but where the functionality of the feature changes I will try and update the image and description.
The Firecapture IO Groups Forum, moderated by Torsten himself, is a mine of useful detail about Firecapture. There is the space there to go into much more detail about particular features than is possible here and you can also ask questions of Torsten and others who are users of the program. Joining the group is a great way to help you solve problems and issues you may have with this great piece of astrophotography software.
If you see a mistake, or think something is not clearly explained, or even is wrongly explained, then please let me know through firstname.lastname@example.org
- ROI- Controlling the ROI Size
- ROI- Controlling the ROI Position
Torsten has built a lot of layout controls into Firecapture to change the appearance and feel of the interface. You can access these controls via the Layout dialog box, accessible via clicking the Settings gear icon, ringed below.
Clicking on this will bring up the main Settings dialog box and under System on the LHS, a little way down from the top, you will see Layout, as ringed below:
The layout controls allow you to change a number of aspects of the appearance of Firecapture.
- Night mode produces a dark background with light lettering more suited to dark adaption at night.
- In Night Mode clicking on colour allows controls over the background colour – redder colouration might be useful depending on your preference
- Unticking Night Mode allows you all sorts of different colour schemes to play with.
- Icon size, font choice and font size are all user adjustable to suit your tastes but again new settings will only be activated on restart.
Below the Night Mode button you have the ability, after restarting the program, to split the main screen into two parts – the main Preview window with the tool bar buttons along its LHS and top, and the Control Panel window. You can see it split up like this below with the Control Panel on the left and the Preview Screen on the right. Splitting it up like this might be useful if you are running two screens in an observatory, for example, and you want the Preview Screen showing on a different display than the Control Panel.
The lower half of the System/Layout dialog box is taken up with choosing which toolbar buttons you want along the top of the preview screen and which you want along the left hand side. You can add from a list of all the commands to either location, remove existing ones or move buttons up or down.
Another method of adding toolbar buttons is to click the + sign at the end of the toolbar row or column on the Preview screen edges. This calls up the list of available toolbar buttons to add. A third method involves right clicking on any toolbar button. If this is done the dialog box below comes up:
The toolbar dialog box allows you to remove the button you right-clicked on, or add new toolbar buttons. It also allows you to add padding between buttons of 0 pixels to 100 pixels in size. This indent feature allow you to group buttons together and improve the organisation of your workspace.
For reference below you will see a complete list of toolbar buttons that you can add into the sidebars as of 2.7.07b. This is a slightly different listing that the complete listing for the options available for keyboard shortcuts shown below:
Firecapture has a whole range of keyboard shortcuts to easily switch features on or adjust settings. Some are set by default (but can be changed), but many others can be set up by yourself. Keyboard shortcuts like this make it so quick and easy to perform specific actions when you are using a laptop in the dark with cold fingers and a dewy scroll pad.
My most often used keyboard shortcuts are:
- Up/down arrows to change gain
- Left/right arrows to change exposure
- Enter to start capture
- Esc to end capture
- X to switch on/off ADC tuning tool
- Y to switch on/off screen adjustment
- V to switch on audible histogram
- P to access Pre-Processing selection box
- Cnrtl + arrows to move ROI
- Cntrl + page up/down to alter size of cut-out
- M to toggle between ROI and full frame
To set up a new shortcut, access the shortcuts menu via System/Shortcuts, pick which key or combination of keys you want associated with the action then click on the action box alongside it. Finally pick the feature you want to associate with those keys from the drop down list that appears.
For reference below you will see a complete list of keyboard shortcuts that you can add. This is a slightly different listing that the complete listing for the options available for toolbar buttons shown above:
Screen adjustment feature allows you to alter the appearance of the preview screen without affecting the recorded data. This is particularly useful to boost the contrast to help with focusing on inherently low contrast objects.
To activate this feature you can click on the toolbar icon or set up a keyboard shortcut to quickly access the ‘Screen Adjustment’ settings screen shown below.
The long button at the top of the dialog box is what you need to click on to activate the feature. Clicking on it will change it from inactive (it will say ‘Enable screen adjustment’ and have a green tick in front of it) to active in which case it will have a red cross in front and say ‘Disable screen adjustment’. Like all these things that are a command rather than an indication of state they can be a bit counter-intuitive, but if you see the yellow warning triangle overlying the toolbar button you know it is currently active. This warning triangle is present even if you click away to remove the dialog box as a useful reminder that what you see on the preview screen will not necessarily look the same as your captured data.
The screen settings available are for adjustment are gamma, brightness and image inversion. You can click on these and immediately see the impact on the preview screen and see whether they help with things like focusing.
A new addition since 2.7.06 is the ability to show the red, green or blue channel individually as this may be of some benefit. To do this click on ‘Channel’ and then pick your colour. The raw data is shown in monochrome and interestingly the green is the least noisy. This is because as there are twice as many green pixels as red or blue in the bayer matrix.
Do be aware that the histogram plot is blind to these new settings and gives a proper indication of what the brightness distribution is like in the data that will be captured. The image can be burnt out on screen and the histogram look okay and the captured data be fine. If the histogram and the captured data are over-exposed there are no preview settings that will allow the image to look okay. You will then see fully-saturated patches – just that they may not be at 100% brightness.
Zoom and Scroll
The zoom function affects the degree of enlargement of the image in the preview screen and can be altered in a number of different ways as described below:
Use the zoom slider, as ringed below, to increase or decrease the degree of magnification by dragging the slider left or right. The actual magnification will be shown in the % box located just to its left. As of 2.7.08 the maximum zoom level is 600%.
Another option is to set-up preset zoom levels by clicking on the % box to the left of the slider. If you do this then a dialog box comes up, as shown below, that allows you to do one of two things. You can either click on one of the preset zoom values in the box or you can click on the line ‘Store current zoom value as…’ Doing this will allow you to allocate the current magnification to one of the Zoom preset icons preset#1, preset#2 etc. Once you have done this you can then add those presets to dedicated zoom preset toolbar buttons as described under the ToolbarButtons section. you can see examples of what those buttons look like in the image above, to the right of the ringed slider.
Another way of increasing or decreasing the magnification is to set up keyboard shortcuts as described earlier. Below I have set PageUp to Zoom+ & PageDown to Zoom-. Clicking on PageUp/PageDown now will increase or decrease the Zoom factor by just 1% for each click which is very useful if you want to set up an exact zoom level, maybe prior to saving against a preset zoom button.
Firecapture has a handy toolbar button you can add to expand the preview to just fill the screen. This is the ‘Fit Preview to Window’ button. Firecapture will pick a zoom level to achieve this and display it in the box beside the zoom slider.
With version 2.7.09 Torsten introduced a very useful Zoom Magnifier Window. When enabled it allows you to zoom right into the pixel structure and easily see individual pixels for diagnostic and analysis purposes. The view in the magnifier window is centred on the tip of the cursor in the preview screen and so by moving the cursor around you can examine different parts of the screen at high magnification.
To access the Zoom Magnifier, click on the toolbar button in the Zoom dialog box (ringed below), add it in as a toolbar button (also ringed below) or create a keyboard shortcut.
The zoom level in the magnifier window is the basic zoom level on preview screen (at the time the magnifier was opened), multiplied by the scaling factor 2x to 20x at the top of the magnifier box. This means that if the zoom level was 600% on the preview screen and 20x was selected that the zoom factor would be a whopping 12,000%.
If you have a zoom level set so high that the whole of the ROI cannot fit on the screen then you can scroll around the ROI by a couple of different methods:
- Left click and drag the scroll bars at right hand side and bottom and drag them up/down or left/right
- Hold the AltGr button down and use the arrow keys to scroll
- Right click and drag the screen. This tends to be very jerky and a bit unreliable.
From version 2.7.07 Beta onwards, Torsten had added a backup feature. The program now creates a new backup each time you close the program and there is the facility to restore the program to any of those stored backups.
Backup allows you to restore all your camera/filter settings and all the custom settings for the features in the program. This is a great help in the event of a big crash where all the FC settings may be lost, or if you have to reinstall the program from scratch.
The program is able to recall all the .cap settings for all the camera/filter combinations for each of the objects (see later under Profiles) and also recall all the ini file settings. You can find what is in the different backups when you look in the C:Users/Yourname/FireCapture/backup folder.
To access backups, click on the ‘More’ button at the bottom of the Control box near the top of the Control Panel. Clicking on this will bring up the advanced camera control dialog box as shown below. At the bottom of the dialog box click on the ‘Restore settings from backup file’.
If you click on this then a new box opens up giving you various backups that you might want to restore the program to:
To restore to a particular backup, click on the backup for your chosen date/time and then click OK to activate it.
ROI- Controlling the ROI Size
The Region of Interest (ROI) is a feature where you reduce the area of the chip used. Only the data in a user-selected region of the chip is then sent to the computer. Reducing the area of the chip like this can allow faster frame rates (if your frame rate is not exposure-time limited) and will also mean less storage space being required per run.
After defining your ROI as described in the sections below, the height of your ROI can be enlarged or reduced by the default keyboard shortcut of holding the shift key down and using the up/down cursor arrows. Similarly the width of the ROI can be changed with shift plus left/right cursor arrows.
Scrolling the wheel of the mouse will proportionally increase or decrease the ROI size.
Defining an ROI – Methods
There are various ways in Firecapture to define the size of the region of interest as described below:
Defining an ROI – L Click and Drag method
I prefer the Left click and Drag method to define an ROI. This is the easiest method to define an ROI as you can easily tailor it to contain the features you want to record and you know just where the ROI will be located.
To use this method you usually start in non-ROI (full frame) mode. In this mode, just hold the left mouse button down and drag the cursor to form a rectangle around the object; then hit the OK button. You can further reduce the ROI size, once you are in ROI mode, by the same L click and drag method.
Defining an ROI – Control Panel Method 1
There are a whole range of other methods to define the ROI but these will locate the ROI at the same position it was last used which many not be where you want it.
At the top of the Control Panel in the Image box, click the arrow on the right hand side to implement the current ROI displayed. If you want, you can type in alternative values for height and length of ROI before then hitting the arrow to action it.
Defining an ROI – Control Panel Method 2
At the top of the Image section of the Control Panel, click the down arrow on the right hand side (ringed) and select one of the displayed ROIs.
Defining an ROI – Control Panel Method 3
There are two ways to access the ROI size and ROI position dialog box. One way is by clicking the ‘X’ in the middle of the ROI size display at the top of the control panel, as ringed below. Clecking on this will bring up the dialog box to define both size and location.
A second way to access this box is by clicking on the option in the ROI dialog box which you can call up as described in Defining an ROI – Control Panel Method 2. In this dialog box click on the option ringed to bring up the ROI size and position dialog box.
Defining an ROI via Preview Pane
ROIs can also be set by right clicking on the preview screen and selecting one of the ROI choices that are then displayed.
ROI/Max size Toggle
You can easily switch between full chip and ROI by clicking either on ROI or on Max in the Image box at the top of the Control Panel. Alternatively you can add the toolbar button for this action to the preview screen and click on that.
My preferred method is to set up a keyboard hotkey (Settings/Shortcuts) and assign a keyboard letter such as ‘m’ to ‘Toggle Max image size/ROI’. Then when you hit ‘m’ on the keyboard it switch between ROI and full frame or back again.
ROI- Controlling the ROI Position
You can control the position of the ROI relative to the borders of the full frame or relative to a planet as described below.
For the ROI to be automatically positioned relative to a planet, Firecapture has to compute the centre of the planet and it can only do this if the profile selected has ‘Planet’ selected under the AutoAlign option. If set to ‘Surface’ or ‘None’ then Firecapture will not be able to automatically move the ROI relative to the object.
Manually Moving the ROI
You can manually move the position of the ROI within the full frame by the default keyboard shortcut of holding down the control key and using the cursor arrows. Each click of the cursor will move the ROI by a set number of pixels. You can alter the size of this step at the bottom of the ROI dialog box – see the bottom of the figure for the section above entitled ‘Defining an ROI – Control Panel Method 2’.
When you move the ROI manually with the cntrl+cursor keys this you will see a schematic showing the relative position of the ROI within the sensor frame. In addition the size and location of the ROI will appear in text above it. You can see this sort of information and schematic in the main figure below for ‘Auto-centre Planet in ROI during Capture’ where you will see a representation of the ROI size and position within the sensor frame and the size/position information displayed above it.
You can centre the ROI in the middle of the sensor frame by clicking on the ‘Centre ROI’ toolbar button – provided you have added it to the toolbar listing. Alternatively you can set up a keyboard shortcut and click on a preselected key on the keyboard.
Centre Planet in ROI
You can reposition the ROI so that the planet sits in the middle of it, by clicking on the ‘Centre planet in ROI’ toolbar button – provided you have previously added it to your toolbar listing.
Alternatively you can set up a keyboard shortcut for this feature and click on a pre-selected key on the keyboard. I like to assign the space-bar to this very useful recentring feature.
The button has the option associated with it to automatically recentre the planet in the ROI if the limb of the planet should reach the edge of the ROI. This will operate whether you are recording or not and can be a bit disconcerting if you don’t realise that it is enabled.
Auto-center Planet in ROI during Capture
Although you can manually trigger the repositioning of the ROI so the planet you are imaging is relocated to the centre of the ROI it is useful to have this happen automatically, especially if the tracking on your telescope is not so accurate. If enabled, then during recording, the ROI will periodically move to bring the planet back to the centre of the ROI. If the planet keeps drifting, the ROI will move in a stepwise fashion across the full frame following the planet as it moves, until the ROI hits the edge of the full frame. Then it can track it no longer and the target drifts off the edge of the CMOS/CCD chip.
Activation of the feature occurs when you click on the feature’s toolbar button or when you click on any keyboard shortcut for the feature, that you may have previously set up for yourself. A tick alongside indicates that this feature is active.
This excellent feature only operates during capture, so if the planet is about to go off the edge of the ROI during preview, use the manual recentring method described in ‘Centre Planet in ROI’ above. Also be aware that this feature (and Lock CofG in ROI during Capture) only work when you select a profile which is a planet, otherwise a centre of gravity of the image cannot be calculated. See Profiles
The Auto-centre function has a very useful feature built-in to it, which allows you to visualise where the ROI currently is within the full frame. Is it near the middle of the chip or is it close to one edge, in which case you might you lose the planet off the edge of the chip shortly. The feature comes into play when the ROI is triggered to reposition itself. At the moment the ROI moves to recentre the planet and for a second or so afterwards a red box appears within the ROI. This red box represents where the ROI is within the full chip – indicating its position relative to the edges. Of course your displayed ROI might be a different shape than the full frame but to understand where it is this way is extremely useful.
Auto-centring of the ROI can be triggered when the centre of the planet moves a little way off centre (Max drift from centre) or when it is close to the edge of the ROI (Min border distance). To change the settings, click on the toolbar down arrow.
For ‘Minimum border distance’ mode, the value you pick is the % distance of the length or width of the ROI for the trigger border region. If the limb of the planet wanders into this border region then recentring of the ROI on the planet is triggered. The limb is detected when FC sees lines of pixels which are more than 10 grey levels brighter than the background (or 100 grey levels brighter if working in 16-bit mode).
For ‘Max drift from centre’ mode the distance is simply the max. distance that the computed CofG of the planet will be allowed to drift from the centre of the ROI, before Firecapture tries to move the ROI to recentre the planet.
As the ‘Auto-centre Planet in ROI during during Capture’ feature tries to do something quite different than ‘Lock Cof G in ROI during Capture’ (see below) the latter is disabled when you select it, to stop them ‘fighting’ each other. If ‘Lock CofG in ROI during Capture’ is enabled when you apply ‘Auto-centre Planet in ROI during Capture’ the then you will get the following message and the Lock CofG feature will be switched off:
Lock CofG in ROI during Capture
The ‘Lock Cof G in ROI during Capture’ feature is similar to the ‘Auto-centre Planet in ROI during Capture’ feature except that instead of the planet being recentred in the ROI it allows you to maintain an off-centre location for the planet. Such a feature allows you, for example, to capture the planet and a moon with the planet on one side of the ROI and the moon on the other side of the ROI. You could achieve this with the planet at the centre of the ROI but you would need a much wider ROI. The feature is much more efficient.
Be aware that this feature (and Auto-centre Planet in ROI during Capture) only work when you select a profile which is a planet, otherwise a centre of gravity of the image cannot be calculated. See Profiles
As the ‘Lock Cof G in ROI during Capture’ feature tries to do something quite different than ‘Auto-centre Planet in ROI during Capture’ the latter is disabled when you select it, to stop them ‘fighting’ each other. If ‘Auto-centre Planet in ROI during Capture’ is enabled when you apply the ‘Lock CofG in ROI during Capture’ then you will get the following message and the Auto-centre feature will be switched off:
Activation of the feature occurs when you click on its toolbar button or when you click on any keyboard shortcut for the feature that you may previously have set up for yourself. A tick alongside indicates that the feature is active. With the feature active, when the planet wanders more than a certain distance from the initial start position the ROI repositioning is triggered. The ROI then moves to bring the planet back to the original offset position.
The offset location within the ROI is calculated when you apply the feature and is indicated by a light cross with a dark border (this works with all backgrounds). If there is nothing in the field that Firecapture can calculate a CofG of then the following message will show:
Although the CofG position is calculated and shown in the preview screen when you enable the feature, as with Auto-centre planet in ROI during Capture, the feature is only active during recording. this means corrections to reposition the ROI to keep the planet aligned with the cross are only made during recordings. Once the recording stops, the cross remains at the original calculated position for the next recording. If you want a new position to be calculated then disable then re-enable the feature to recalculate the CofG.
You can adjust the position of the CofG cross, both before and during recording, using Alt+arrow cursors if you have it enabled in keyboard Shortcuts.
You can decrease or increase the amount it can drift before activation by clicking on the down arrow associated with the toolbar button. The dialog box which then comes up is shown below.
Speeding up the responsiveness of automatic movement of ROI
The default rate at which the ROI is repositioned to keep a planet in a central position (for ‘Auto-centre Planet in ROI during Capture’) or in an offset position (for ‘Lock CofG in ROI during capture’) is once every 3 seconds.
If your telescope tracking is not great, or you experience windy conditions, then an adjustment of the ROI once every 3 secs may not be enough to prevent the planet occasionally moving outside the ROI. In this case more frequent shifts in position of the ROI would be beneficial. You can speed up the responsiveness of the ROI movement by editing the Firecapture ini file found under Users/YourName/Firecapture on your C:drive. Search for the LongTasksEverySeconds or LongTasksEveryMilli and try reducing it to 1second or 1000 milliseconds as appropriate. Save the file after making changes and reopen Firecapture.
Auto-align is a feature which stabilises the planet’s image in the preview screen. The data downloaded from the ROI is shifted in X and Y to keep the centre of gravity in a central position on the screen. The feature is especially useful to aid in achieving accurate focusing, as it removes movement due to mechanical movement due to the focus motor as well as any movement due to the atmosphere, both of which help achieve the best focus.
Auto-align can be activated by clicking on the toolbar button or by associating it with a keyboard shortcut and clicking that key. I assign the keystroke ‘a’ to the feature. A tick alongside indicates that the feature is active.
When auto-align is activated the planet looks as if it is staying central within the ROI defined on the chip- but that is an illusion, the planet may actually be close to drifting out of the ROI. To know where the planet is within the ROI the feature uses 4 small red boxes to mark the true position of the planet within the ROI. In the figure above these squares are close to hitting the edge of the preview frame. If they do then the planet will start to go off the edge of the ROI and the planet will appear cut-off on one side although it will still be central on the screen. To bring the planet back into the middle of the ROI the latest versions of Firecapture allow you to use the ‘Centre in ROI’ feature in conjunction with Auto-align. I recommend associating a keyboard stroke such as the space-bar with the ‘Centre in ROI’ feature, then, when the 4 red boxes are close to the edge of the preview screen, you can just hit the space-bar to bring the planet back to the central position.
Auto-align can be used during preview and also enabled during recording in which case the planet will be kept central within the recorded area. So that the planet stays approximately central in the ROI during recording so eliminating the danger of a chopped-down planet you could enable ‘Auto-centre Planet in ROI during Capture’.
CutOut, which was at one time known as Crop video, is a very useful feature which can save you loads of hard-drive space by just recording the part of the ROI frame with the planet in it. Smaller videos area also much quicker to process in AutoStakkert!
CutOut can be activated by clicking on the toolbar button or by associating it with a keyboard shortcut and clicking that key. I assign the keystroke ‘c’ to the feature. A tick alongside the toolbar button indicates that this feature is active.
When CutOut is active a yellow box surrounds the planet. If you have ticked the option ‘Let the CutOut Box follow the Planet’ (see figure below) the yellow CutOut box closely follows the planet. Above the box it will say ‘CutOut’ and give the size of the CutOut box in pixels. CutOut again only makes sense for profiles defined as planets so won’t work for things like lunar landscape videos.
CutOut usually used in combination with a suitable ROI. The ROI is defined at the camera end and the data within the ROI is transmitted to the computer during capture. However, when the CutOut feature is active, Firecapture analyses the ROI and just saves the data within the smaller CutOut box – anything in the ROI outside the CutOut is not recorded. The yellow box tracks the planet closely and can respond to movements of the planet much more quickly than the ROI so the recording that you end up with has the planet pretty stationary within it. This is the fundamental benefit of CutOut over ROI – its much greater speed of response to changes in position of the planet, which then allows a much tighter box to be defined.
CutOut will work without using an ROI but if you operate in that way the whole full frame will be downloaded to the computer before the CutOut is applied and this may severely limit the maximum frame rate. Better is to use a smaller ROI to improve the frame rate, but which is still quite a bit larger than the planet, then use a significantly smaller CutOut tailored much more closely to the size of the planet. Having said this, with some older cameras you are not able to define an ROI on the chip. In this case CutOut becomes a very valuable way of reducing storage space and speeding up post-processing.
Using the ‘Auto-centre Planet within ROI during capture’ feature with the ROI and the CutOut feature active will mean that if the planet drifts the ROI will reposition itself from time to time to keep the planet in the ROI. If you don’t use this feature or don’t manually move the ROI to keep in view the planet may drift out of the ROI and the CutOut will lose the planet – as a result you will then be recording an empty CutOut box.
Defining the size of the CutOut box
When the feature is active the CutOut box can be redrawn to a different size or shape by holding the Alt key down whilst left clicking and dragging. Forgetting to hold the Alt key down will just mean you redraw the outline of the ROI- which you can then cancel. If you define your CutOut box then apply an ROI where the ROI is smaller than the CutOut then the CutOut size matches the ROI size which is rather pointless as all the benefits of using a CutOut are lost.
You can increase or decrease the size of the CutOut by holding the Cntrl key down and using the Page Up/Down buttons. The buffer resets after each resize step. The pixel step size for this increase or decrease in the size of the CutOut box is set in the feature dialog box which can be accessed using the down arrow on the toolbar button (see below). An alternative method to resize the cut-out box is to hold the Cntrl key down and use the scroll wheel on your mouse.
The dialog box that comes up when you click on the ringed down arrow above reminds you all the methods for defining the CutOut size. You get the same information is a different format by clicking on the CutOut toolbar button as shown below.
Enabling the debayer function by ticking the toolbar button converts the data being sent from a one-shot colour camera into a correctly displayed colour image on the preview screen.
A one-shot colour camera has a pattern of colour filters over all the sensor elements and typically they are arranged in repeating blocks of 2×2 pixels containing 2 greens, 1 red and 1 blue. This means half of the sensor elements on the chip are green, whilst a quarter are blue and a quarter red. To decode the data read from the chip and to correctly display the colour image Firecapture has to know what the particular pattern of filters is in the block of 2×2. With the proviso that no green elements are adjacent, then four possible arrangements are possible for the colours: RGGB, GBRG, GRBG, and BGGR – known in abbreviated form as RG, GB, GR, and BG.
The correct bayer pattern is programmed in to Firecapture for some cameras and colour displays correctly when used for the first time. For others though you will need to click on the down arrow at the RH end of the Debayer toolbar button and select the debayer pattern it from the listing. Often it is trial and error to pick the right one and something best done on a daylit colour scene.
Debayering creates a potentially much larger file size as a 640×480 colour chip will, for each frame, produce a red image of 640×480, a blue image of 640×480 and a green image of 640×480. Consequently the file size will be 3x larger and the data generation rate will be 3x higher, possibly leading to a reduction maximum frame rate. It is for this reason that Torsten has, by default, arranged to preview the video on screen in colour, but record the frames in RAW undebayered mono, as this minimises storage requirements and maximises the fps.
Storage and fps considerations aside, the choice of debayer algorithm has a bearing on the quality and resolution of the final colour image. It is much better to debayer later with a good algorithm than use a fast debayer method and end up with permanently degraded colour data. The best method for debayering is the default method used in Autostakkert which builds up the ‘missing’ coloured pixels not by interpolation but by a ‘drizzle’ method using real data. In this case no mathematical predictions are required and the colour data is reassembled at the full chip resolution. Another very good reason to leave the data undebayered (mono) for a colour camera when recording.
Until quite recently the preview would be in mono during capture reverting to debayered colour when the recording stopped. From FC version 2.7.03, however, when debayer is ticked the preview is in colour regardless of whether or not you are recording. You can force Firecapture revert to the older action of the preview being in mono during capture by ticking the option ‘Disable debayering of preview whilst recording’. Ticking this setting gives you an extra visual clue that you are recording, but removes the a key benefit that colour preview brings during capture, which is an improved ability to refocus during your recordings.
Although not recommended, for the speed and data storage limitations described above, you can force Firecapture to record in colour if you wish by ticking the ‘Force record in colour’ option under the debayer selection list (see figure above). This might be useful for test purposes or for single frame generation where you might want to view the debayered result right away. NB In 16-bit mode you cannot force Firecapture record in colour, you can only record in raw undebayered mode.
Do note that unless ‘Force record in colour’ is ticked, the data recorded via Firecapture is always in the preferred undebayered state (not in colour) regardless of whether the debayer toolbar button is ticked or not ticked. Really the debayer button now applies just to the preview screen and whether that is displayed in colour or not in colour.
The other option seen in the debayer dialog box above is the interpolation algorithm. As I said earlier debayering takes a mono 640×480 image and from it produces a red image a blue image and a green image each of which is 640×480. Firecapture has to create these from incomplete data, as the green data has only half this number of picture elements whilst the red and the blue have only a quarter. To populate all 640×480 picture elements, an interpolation algorithm has to be selected to, for example, to meaningfully fill in the blank 3 red picture elements surrounding each single real red pixel. The debayer dialog box is where this is selected. Unless you are following the not-recommended route of saving in colour, the exact choice of debayer interpolation algorithm is of little importance as the data is saved undebayered ie without applying any debayer algorithm. The choice will however subtly affect the appearance of the colour preview. The choices are ordered in terms of processing power and complexity. The later ones in the listing, SmoothHue, AdaptiveSmoothHue, and VNG, require a lot of CPU power and should be avoided. NearestNeighborFast is the multi-core version of NearestNeighbor. By default NearestNeighborFast is chosen and should be more than adequate for the preview screen colour rendition.
One of the settings you will see in the Debayer dialog box is the Y800/Y16 mono tickbox. Ticking this will output an uncompressed monochrome video file when you hit capture. What you get depends on the camera type and whether you are operating in 8 bit or 16 bit mode:
- Y800 for colour camera. Debayer using nearest neighbour algorithm to produce R,G and B value at each pixel site. At each pixel site average the R, G and B by adding together (and then dividing by 3) to product a mono 8-bit value
- Y16 for colour camera. Debayer using nearest neighbour algorithm to produce R,G and B value at each pixel site. At each pixel site average the R, G and B by adding together (and then dividing by 3) to product a mono 16-bit value
- Y800 mono. Raw 8-bit value at each pixel site
- Y16 mono. Raw16-bit value at each pixel site
For colour cameras if you tick this box you will lose the ability to debayer the data layer and retrieve the colour information – so use the feature with care. You can always do this sort of processing later, so if in doubt record in raw undebayered mode by leaving this box unticked.
The histogram feature in Firecapture allows you to see the brightness distribution of the pixels that are in the ROI and indicates what the pixel brightness distribution will be in the captured data. This information will help you adjust the gain and exposure appropriately – ensuring the image is sufficiently bright to prevent quantisation errors but not so bright that areas of the frame are saturated.
Anything that affects the pixel brightness in the recorded data (eg pre-processing functions like contrast or gamma adjustment) will affect the data displayed in the histogram. Some features such as ‘Screen Adjustment’ affect the view on the preview screen but have no effect on the data – these settings will have no impact on the histogram data displayed.
Ticking the histogram toolbar button will display the histogram in the control panel on the LHS of the screen but you can also have further histogram plots displayed at the bottom of the preview screen by enabling the options appropriately. Clicking on the down arrow on the histogram toolbar button brings up an options box which if you click on will bring up the histogram settings box (see below). This then allows you to control the display of the histogram feature.
The ‘Show histogram in preview screen’ option allows you display pixel data either as a simple Horizontal bar or as a Full log-scaled histogram at the bottom of the preview screen. When you select this option other data is also shown – the same information that shows up on the left hand side of the small histogram described below, also shows in the upper left hand corner of the preview screen.
Below the ‘Show histogram in preview screen option’ is the ‘Show Emil Kraaikamp Noise estimator (mono cameras only)’ option. To understand what this is all about just click on the ? button alongside (warning it’s quite advanced stuff!). If you tick the noise estimator option and you also have ‘Show Histogram in preview window ticked then the information in the upper left hand corner of the preview screen will also display the signal to noise ratio (S/N). Despite the legend ‘mono cameras only’ the S/N value will be shown for colour as well as mono cameras.
The Horizontal bar mode is shown in the figure directly below at the bottom of the preview screen and shows the range of brightnesses of the different colours for a colour camera. For a mono camera there would be just a single bar rather than three parallel ones. Horizontal Bar mode is a simple display mode with no indication of the number of pixels of a particular brightness. Instead the right hand end of the bar indicates the brightness of the brightest pixels of that colour as a % of the maximum before saturation (100% is saturated). This is the mode I generally use as I like its simplicity – it just tells me how close to saturation I am for the different colours and allows me to easily set my gain/exposure/colour balance so that the highest value in the bars is about 80% to 85%
Clicking on the ‘Full log-scaled’ option instead displays a fuller histogram at the bottom of the preview screen with information about the number of pixels of each brightness. I find this a little over-complicated and the different colours block each other as the three sets overlap for a one-shot colour camera, although this would not be an issue for a mono camera with only one graph. The histogram rather blocks too much of the preview screen.
At the bottom of the histogram dialog box there are options for the way in which the histogram is displayed in the control panel on the left-hand side. The histogram can be displayed in one of two formats for one-shot colour cameras. If ‘stacked’ is ticked, then the three colours are shown as in the image below with bars representing the current maximum peak for each colour and a distribution plot for each colour over-laid on one another below the set of bars.
Note that the white line at the right hand side of the brightness information box, which is on the left hand side of these mini histograms, is the zero brightness marker. At the other end of the scale is the maximum brightness level. For 8-bit imaging maximum brightness is 255 whilst for 16-bit imaging the maximum brightness is 4095.
If you tick ‘Separated’ then the three colours are separated out with red at the top and blue at the bottom allowing you to get a much better feel for the separate distribution for each colour. A vertical line at the right hand end of each plot shows the maximum current brightness for that colour – a bit like the RH end of the bars in the mode described above.
For both the Separated mode and the Horizontal bar mode the maximum brightness is displayed numerically on the left hand side as a brightness count and also as a percentage of the 100% saturation level. The brightness count is shown as the maximum brightness for that colour but also the minimum brightness. For example 0/173 means that the dimmest pixel is brightness 0 and the brightest is 173. The minimum brightness is usually 0 in normal night-time imaging, but this may not not the case with imaging the Sun or Moon or if imaging in the daytime – in such a case the minimum brightness might be well above 0.
Another really nice feature that Torsten has built in to Firecapture, is the pixel brightness and position reading for the current cursor locationn in the preview screen. To enable this option tick the option in the main histogram dialog box ‘Show pixel value and position in separate line below histogram’.
The RAW brightness of the pixel, at the location where the cursor stops, is posted at the bottom of the histogram as seen below (where the brightness is 39). For one-shot colour (OSC) cameras the colour of this text matches the colour of the bayer filter on the pixel at this location. The brightness value updates every few seconds even if the cursor does not move. The X and Y position of the cursor relative to the top left hand corner of the chip is also displayed under the histogram, together with an estimate of the general screen signal to noise ratio.
For the stacked type of display the pixel brightness is shown at the bottom left hand corner. In the image below we also see the signal to noise ratio (S/N) as described above.
In case you wondered what the histogram looks like for a mono camera this is shown below – nice and simple and a combination of the Stacked and Separated types shown above with one bar and one distribution plot. For mono cameras there is only this combined mode and ticking the different Horizontal bar/Stacked options makes no difference.
Once you switch filters in a recording session Firecapture not only displays the current maximum brightness value but also the maximum brightness during capture for the previous filters that were used in recordings. You can see an example of this below for a mono camera where the current filter was an 807nm filter but previously a 642nm and 742nm filter had been used. Only the maximum brightness values during capture are recorded so don’t expect a marker if you did hit the record button on a previous filter. Colour cameras work in a similar way except that a marker is entered for each colour for each previous filter.
Note in the figure above, that markers are also laid down on the histogram at the bottom of the preview screen (if you selected the histogram to be displayed there too). The markers here are the triangles you see at the right hand end of the histogram. The markers are in the colour of the filter icon and are not annotated – in the example here both had the same filter colour icon so both are deep red.
Another option in the histogram settings box is the ‘Show colour histogram in RAW mode’ setting. Ticking this gives you histogram information for all three colours for one-shot colour cameras, even if the display switches to monochrome during capture as a result of selecting that older functionality in the debayer settings (by having ‘Disable debayer while recording’ ticked in the debayer settings – see user Debayer section here). With the more modern functionality when the preview screen remains in colour during capture ticking this has no effect the plots continue display as separate R/G/B.
Histogram calculates the pixel brightness distribution at a default rate of 2Hz although this can be changed at the top of the dialog box. Another available setting is the pixel block mode which by default is 4×4 pixels but can be set from 1×1 to 10×10. The default 4×4 means that Firecapture using brightness data from every 4th column and every 4th row down. This reduces the processing load on the CPU
The ‘calculate histogram in separate thread’ option is best explained by Torsten himself: By default the histogram will be calculated in the cam worker thread which also reads the images from the camera. If the image has been read the histogram will be calculated. Depending on how much time the system needs this may add some latency resulting into a lower effective frame rates. ‘Calculate histogram in separate thread’ will force running the histogram calculation in a separate thread so calling it inside the cam worker will return immediately removing any sort of latency.
A very useful but rarely used feature of Firecapture is the Histogram Sounding button which you can add to your toolbar set or set a keyboard shortcut for – I use the keyboard letter ‘v’ to activate.
Enabling this feature gives an audible tone whose repetition frequency is brightness dependent. With this enabled you can tell your planet or other object has entered the ROI without even looking at the screen. This is useful for attempting to locate objects whilst looking through the finder. The feature comes into its own as instant feedback when tracking the ISS whilst following it through the finder giving encouragement to stay on target!
Print Timestamp into Data
Here is another useful Firecapture feature. This one prints a timestamp into the frame, for recordings where the timings are important. When the feature is enabled, the time in UT is printed into the top left hand corner of each frame as in the figure below. The timestamp appears in the preview frame too when not recording.
For highly accurate timings, such as occultations, even when the clock has recently been synchronised, there are complex reasons that the recorded frame times may be not be as accurate as you may at first think, with sub-second errors creeping in. In those cases it is better to rely on other methods that are more accurate and advice needs to be sought from occultation observers such as the BAA asteroids and remote planets section. You can read much more about the accuracy of the timestamp in this thread on the Firecapture IO Groups Forum.
Reset Capture Counter
When referring to your files during recording sessions in any note taking, or later when processing, it is really handy to have a shortened name to describe each of the videos, rather than writing down the time that it was taken. This is where the Firecapture Capture Counter comes in.
Under Capture Settings if you tick the ‘Capture counter’ option in filename properties then Firecapture will add an ID number, starting at 1, to the filename in the order specified in the Filename properties area of the dialog box. The index number will increase by 1 each time you record a file.
If you start a session within 8hrs of the previous one, then the index numbering will continue where the previous session ended and won’t reset to 1. If you want it to reset to 1 just click on the Reset Capture Counter toolbar button
Profiles are key to the power of Firecapture but can be baffling for the beginner to understand, due to their complexity. It is useful to describe them here.
Profiles are combinations of either connected camera plus target (such as Moon or Mars) or connected camera plus target plus filter in use. Camera settings and recording settings are saved against these different combinations and if you quit Firecapture the last used settings are saved. This means that if you connect the same camera at a future date and select the same object and select the same filter, those previous settings are recalled. This is a great time saver allowing you to be quickly recording after changing target but can trip you up if you forget to click the right target profile or filter.
To change profile you will need to change any one of the following camera, target choice or filter choice . Changing camera requires you to quit Firecapture, disconnect the old camera, reconnect the new, then restart Firecapture again. If the camera is not automatically detected, select the manufacturer from the listing that appears. Note: If the camera then doesn’t start it is usually a driver installation issue or camera fault.
Once the camera is connected, pick your intended target and the filter you are using from the Capture box in the control panel or by clicking any target and filter toolbar buttons that you might have installed in the toolbar. The figure below shows that control panel Capture box and indicates that Venus is selected with an L filter. Click on either of these items to see the whole list of available targets/filters.
It may be obvious but I will say it anyway. Firecapture does know what camera you have connected but cannot know what planet you are looking at or even what filter you are really using. By clicking on the target and filter you are telling it what you are currently using. Firecapture then makes choices of features and settings that should be suitable for that combination but it is for you to check how appropriate they are and to refine them.
Target and Filter Profile Editing
At the bottom of the planet selection box that appears when you click on the planet button in the Capture box is an ‘Edit profiles…’ button. Likewise a similar ‘Edit filters…’ option is available at the bottom of the Filter selection box.
Target profile settings
Below is the box which appears when you click on target ‘Edit profiles…’ button.
The available targets are shown in the list. You can change the order in the list and it will change the order in the target pop-up box. To change the order highlight the target and use the up/down arrows to promote or demote it in the list. You can also remove unwanted targets or use the +Add button to create a new target.
When you create a new target you are prompted to first give it a suitable unique name (note; no spaces, commas or underscores allowed in the name). After this you should then associate it with a Target from the restricted list upper right which will determine the icon appearance. Lastly you pick the AutoAlign profile whether it is a planet (a blob), a surface (like the Moon close up) or NONE. Your choice has a bearing on the functionality of Firecapture when that target is selected, particularly the use of features with some aspect positional determination. Features below will only work properly if ‘planet’ is chosen as the AutoAlign option for that target:
- Auto-centre Planet in ROI during Capture
- Centre Planet in ROI
- Lock CofG in ROI during Capture
Below is the box which appears when you click on target ‘Edit filters…’ button.
As with targets you can promote, demote add and remove filters in much the same way as described above. New filters need to have a unique name and the colour of the filter icon chosen either by clicking on the ‘Use RGB/colour icon’ to give it rainbow colours or by clicking on the Change colour box below this. There is a huge number of ways to pick a colour but probably the easiest is to pick one from the Colour Swatches grid mode as shown below.
The colour chosen for the filter has a bearing on how the filter icon colour is shown and the colour of the maximum brightness markers in the histogram window (see under Histogram section). The colour also affects the colour of the capture details text that appears at the top of the screen if you have selected ‘Display capture details in preview window’ Preview/Display settings.
Filter & Target Filename
As a useful reference the filter name and target profile name can both be made to appear in the filename if you have selected that in the ‘File name properties’ listing under Capture/Settings.
Influence of Camera, Target and Filter on Camera Settings
Below is the full list of settings that are stored against either the combination of camera + target or against camera + target +filter. This is probably the most important figure in this section on Profiles and tells you what settings are saved for each unique combination:
If you click on the More button (but not the down arrow) which is located below the Exposure slider in the control panel then a camera settings dialog box will appear as below:
If you then click on show all values a table will appear of many of the camera settings which have been saved for each filter and for each target combination for that camera. To change the target click on the object icon upper left. A typical table is shown below (click to enlarge).
The information is for information only and cannot be edited here but it does allow you to check all the combinations for anomalies. Be aware that many combinations are not used and are filled with default irrelevant values.
Firecapture has several features that indicate that a video is currently being recorded and these will be covered in this section.
Until version 2.7, when using a colour camera, a big clue that a recording was in progress was that the preview screen would switch from a debayered colour preview to an undebayered grey one. With v2.7 that changed – the preview screen now stays in colour whilst the recording is raw and undebayered (unless specific special options are selected – see Debayer section). Despite no longer having this change of the preview screen as a reminder that Firecapture is recording data, there are many other visual and audible indications that capture is in progress. There is also a dialog box which pops up if you try and close Firecapture before a recording is finished.
When capture is in progress, the Record button in the Capture section of the Control Panel will flash, alternating between a Red Arrow and the word REC. The same will happen to the record button if you have added it as a toolbar button.
You can see the record button is situ in the Capture section of the Control Panel below.
Below the Capture box, the Status box gives data on the progress of the recording, showing frames saved, time elapsed the recording index number and the time remaining. The latter is also shown in graphical form in a small apple pie chart in the bottom right hand corner of the screenshot above.
Further indication that a recording is in progress is see displayed in bold characters as Capture Details above the preview screen, if you have selected that option under Settings/Preview/Display by ticking ‘Display capture details in preview window’.
The information displayed above the preview screen during capture can be customised by picking items from the menu below the check box, as well as selecting options on where the information is displayed and its size and scaling factor. Just experiment with the settings to suit your preferences. One really neat touch to this feature that Torsten has added is that the colour of the font of the capture information matches the colour of the filter icon you have selected.
The neat idea of making the font of the capture details that show during recording, match the colour of your filter selection, has a potential downside. If you have a red filter selected and also have a night-safe red background behind your preview screen, then you have a red text on red background situation and you can’t read the text! To overcome this there is an option in the display details to add a grey background behind the text, which you can see on the right hand side in the dialog box above.
When the grey text background is selected as above, the capture details will now show up with higher contrast as seen in the image below. It is a good idea to set this up as a keyboard shortcut in case you have a filter which has a grey colour. I know this is unlikely but you don’t want then to face text a grey on grey background situation!
As well as visual clues that a recording is in progress, an audible acknowledgement is a popular option. This is enabled by ticking the option ‘Do a short beep when starting/stopping capture’ under Settings/General. Make sure your laptop is not muted so you hear the beeps!
Capture File Formats
Firecapture can record in several different image and video formats. To chose the format to record in you need to click on the file type in the Capture box in the Control Panel as shown below.
Note the option to always use the same file type at bottom of the selection box which fixes the format for all filter choices for the current camera and object combination.
Different formats selections are available for standard 8-bit recording and for 16-bit recordings as per the table below:
The exact choice of format to record in is beyond the scope of this webpage but my preference is SER format for video and PNG for single frames. SER is an uncompressed video format which is more tightly defined than AVI and has the advantage that recorded videos can be easily reviewed or modified in Chris Garry’s excellent SERPlayer program. SER is accepted by stacking programs like Autostakkert! and Registax. PNG is a lossless compressed format which can be 8-bit or 16-bit being compressed file sizes are much smaller than uncompressed TIFF files.
High Speed (HS) and USB Speed Setting
The camera’s frame rate (frames per second or fps) is often a concern for planetary imagers, as this determines the number of frames that can be captured in a given time and can have a big bearing on the quality of the stacked image. For longer exposures, the fps is just dictated by the exposure time. For example, if the exposure time is 50msec you cannot run at more than 20fps. As the exposure time drops, however, the fps goes up and the rate of data transfer increases – more digital data gets set to your laptop in a given time. Eventually you reach a point where the fps is no longer the inverse of the exposure time and you are then data-rate limited rather than exposure-time limited. The frame speed at which this occurs depends on the choice of camera, the height of your chosen of interest (ROI), but also other Firecapture settings.
For ZWO and QHY cameras the maximum fps before you are data-rate limited is affected by the setting of the USB slider found by clicking the ‘More’ button at the bottom of the Control box at the top of the control panel. For ZWO cameras, too low a USB setting limits the maximum fps, but if you set the speed at too high a value then capturing can be unreliable with lost frames and failed captures occurring. For QHY cameras the slider is inverted compared to that for ZWO cameras, so 0 is the highest speed and 100 the lowest. In that case too low a value can lead to lost frames and failed captures, whilst too high a value puts the brakes on the fps but keeps it reliable.
Another way to increase the fps, if you are data-rate limited, is to tick the HS or high speed box, if that option is available for your camera. For ZWO cameras, ticking HS mode increases bandwidth by reducing the bit depth that the sensor’s Analog to Digital Convertor (ADC) operates at – dropping it from the usual 12-bit to 10-bit operation. Because the digital output of the camera will later be cut back to the most significant 8-bits, you cannot tell from the data retrospectively if the sensor ADC was running at 12-bit or 10-bit except by knowing if HS was ticked or not.
To know if HS is ticked there are now several features built into Firecapture to help you. First is that if the HS is ticked then you will see ‘HS’ appear in small text at the top of the preview window, as ringed below. The size of this text can be altered at the top of the large ‘Display’ dialog box seen in the Capture Notification section. You can also get an indication that HS is ticked if you select that option in the capture details menu (see the bottom of the large ‘Display’ dialog box in the Capture Notification section). If you tick that, then when you are recording ‘HS’ will appear in the text string that appears at the top of the preview screen (see ringed on right-hand-side in the example below).
If you want to know retrospectively for a recording if HS was ticked, then look for Yes/No against the ‘HighSpeed’ line in the log file, automatically generated along with your capture data file.
Although ticking HS mode can often double the frame rate when imaging large areas at short exposures, you should be aware that there will be a small increase in read noise in the resulting video frames. Generally, however, the main cause of noise in the stacked image is shot (quantum) noise rather than read noise so the increase is rather academic and the extra frames in the stack that are generated should more than make up for the slight increase in read noise. Even so, if you are not data-rate limited but instead exposure-time limited, then it is a good idea to untick HS mode
You should also be aware that in 16-bit mode ticking the HS box has no effect on the ADC bit depth or the camera speed. The ADC bit depth stays at 12-bit for most cameras (FC adds 0000 to the end of the 12-bit data to make it 16-bit, 2 bytes long, which is much easier to handle.
A planetary imaging camera normally outputs a signal with a bit depth of 8-bits which means that the signal can go from 0 (=0000 0000) up to a maximum reading of 255 (1111 1111) – there are 256 possible grey levels. When hundreds or thousands of images are stacked in stacking software like Autostakkert! the stacked image has a much greater number of grey levels, as the output frame now has a bit depth of 16. This 16-bit image has 65536 grey levels allowing the image to be stretched and processed without the image breaking up, with grey levels staying smooth and continuous rather than showing steps in brightness (quantisation noise).
The analog to digital convertor (ADC) in the camera converts the analog output from the sensor into a digital signal and generally work at a greater bit depth than 8-bit. Usually they work at 12-bit or sometimes 14-bit. You can access this greater bit depth by ticking the 16-bit checkbox in the Image box at the top of the control panel.
When you tick this box you do not have a full 16-bit depth, with 65536 grey levels, as the 16-bit is actually made up of the 12-bit (or 14-bit) output from the ADC with 0000 added onto the least significant end. Forming the 12-bit output into a 16-bit format like this makes it much easier for computers to handle as by convention they like their data in multiple chunks of 8-bits (called 1 byte).
It might be useful at this point to have an example to illustrate matters!
|Sensor Pixel Value||From 12-bit ADC||Converted to 16-bit||If 8 bit|
|3899||1111 0011 1011||1111 0011 1011 0000||1111 0011|
The 16-bit signal, because it is really just a 12-bit with 0000 on the end, has only 4096 grey levels and the maximum value is 65520 not 65535. If you want to read more about this have a look at the bottom of my page here.
The above is true of a lot of digital video cameras working in 16-bit mode, but ZWO cameras operate differently. For them the 12-bit (or 14-bit) signal is stretched to the full 16-bits in this higher bit depth mode and the byte pair does not have 0000 at the end. These cameras still have 4096 levels (or 16384 levels for a 14-bit ADC) but the range is stretched so it extends from 0 to 65535 (to be checked)
Normally 8-bit imaging is perfectly fine for planetary imaging as after stacking the stacked image is full 16-bit, however, there are a few occasions where you might want to consider ticking the 16-bit box to use frames with a greater bit depth:
- Occasions where you might be stacking just a few frames or wanting to extract single frames of as high a quality as possible. Such applications might be, for example, DSO imaging, ISS imaging, or pulling out frames of short-lived events like Jupiter impacts.
- For very bright objects with very low gain the shot noise in pixels may be so low that stacking multiple frames does not properly form smooth 16-bit stack and the stack is afflicted with quantisation noise. For more on this see this interesting link to a discussion on this on Cloudy Nights.
- In very dim objects that you want to image details within, the shot noise in pixels may be again very low. Again this can lead to issues with quantisation noise and poor rendition. Examples might be imaging night-side of Venus in IR; details in the Crepe ring of Saturn; details in lunar shadows.
Do be aware with 16-bit imaging that as each frame is 2 bytes rather than 1byte, the frame speed, if data-speed rather than exposure-time limited, (read section on High Speed (HS) and USB Speed Setting) frame rates can be significantly reduced as each frame is twice the file size.
Ticking the 2x binning check box groups a square of 4 adjacent pixels together, reducing the overall number of pixels in the image by a factor of 4, but increasing the effective area of each pixel by the same factor. Video data size is also decreased by 4x as a result of enabling Bin 2x.
As far as shot noise (aka quantum noise) is concerned, 2x binning increases the signal to noise by a factor of 2, as the shot noise adds together in quadrature (ie Bin2 shot noise = sq rt (nA2+ nB2 + nC2 + nD2), making it just twice as large, whilst the signal is boosted by 4x.
For CCDs binning is done with the analog signal and helps with read noise. Binning increases the signal size but as the binning is done on the chip for CCDs there is only one portion of read noise for the set of pixels binned. So if you had 4 pixels binned there would be one portion of read noise instead of 4 portions, for a signal that was 4x larger. Thus for CCDs binning does not increase read noise and the SNR increases in proportion with the number of pixels binned, in our example SNR increases 4x. For CMOS chipped cameras the binning is different as the read noise is done digitally and for Bin2 is read four times, once for each of the pixels in the binned group. Like shot noise the read noise is random so adds in quadrature. So, like before, the read noise increases by 2x whilst the signal increases by 4x thus the overall SNR increases 2x. For most planetary imaging, unlike DSO imaging, read noise is relatively unimportant and it is the shot noise that generally dominates.
Another advantage with binning for CCDs is that read speed is increased as you are reading 1/4 the number of pixels. For CMOS cameras there is less benefit to speed. See the examples below:
- For the ZWO ASI174 camera the 2x binning is done in the camera, off the chip, by hardware and software. The max. speed without binning is given as 128fps for the full resolution of 1936X1216 and the same 128fps applies for 2×2binning where the resolution drops to 968×608. This compares to about 250fps for unbinned 968×608
- For the ASI120 camera the 2x binning is done in the camera with software only. For this camera the max speed is given as 60fps for the full resolution of 1280×960 but for 2×2binning where the resolution drops to 640×480 the speed drops to 45fps. This compares to 133fps for unbinned 640×480.
Don’t think that binning will make the pixels brighter, it won’t, 4x as many electrons are collected together but the electron well is effectively 4x deeper so the average grey level is unchanged.
Binning will obviously increase the effective pixel size, halving the image scale and potentially compromising resolution. For planetary imaging you satisfy the Nyquist Criterion by having 3 pixels across your minimum diffraction feature which means for a mono camera having an f-ratio which is 3x-5x the pixel size in microns (higher in better seeing conditions). To still satisfy Nyquist for 2x binned pixels, you would need to double the f-ratio of your set-up. This then means the same light that fell on one pixel before now falling on 4 binned pixels and the overall signal for the pixels (unbinned/binned) hasn’t increased. Thus the shot noise is the same as before but the read noise has doubled. For DSOs this would be a bad idea, but for planetary imaging where read noise is of minimal importance, it won’t make much difference.
As you can see there is little benefit in binning unless you are trying to get closer to Nyquist by matching an existing camera with a particular optical set up. For example, if your only Barlow gives you f28, but your only camera has 2.9um pixels then dividing 28 by 2.9 gives you 9.6. With this set-up you would be massively oversampling. Bin the camera 2x though and you have a camera with twice the read noise (likely unimportant) but the effective pixel size would be 5.8um so giving a ratio of 4.8 and now properly satisfying the Nyquist Criterion.
Binning can be done in the processing later to help reduce shot noise, so really the only benefit of binning for CMOS cameras is a reduced video file size. The downside of ticking the binning box here, however, is that you can’t undo the binning later!
Do note that you can use binning for colour camera too. 2x binning groups together not 4 immediately adjacent pixels but 4 nearby pixels of the same colour. The diagram below hopefully explains how the binning works for mono and colour cameras:
I’m unsure of whether 2x binning is available in 16-bit mode – I need to check.
ADC Tuning Tool (colour cams only)
Firecapture has a selection of tools for tuning an atmospheric dispersion corrector (ADC) which are enabled by clicking on the icon, or activated by clicking on any associated keyboard shortcut that you may have set up. The tools are only available, and indeed have any meaning, for one-shot colour (OSC) cameras.
Clicking on the down arrow at the right-hand end of the tool icon will bring up the tool dialog box which allows you to select which one of the tools will be used when the feature is enabled. The settings and sliders that show in this box depend on which tool you have selected and are different for different tools, as you will see.
Personally I think the Edge-Tinge tool is by far and away the simplest and best of the available tools and allows you to adjust the ADC orientation and lever settings with great precision. Although the most recent tool added to the armoury I will cover it first but also describe the other tools for sake of completeness.
When light enters our atmosphere at an angle, the sky acts as a huge prism, angularly raising the object in the sky by an amount which depends on the altitude of the object. The lower the object in the sky the greater the induced elevation. The degree of lift is also wavelength dependent and the net result of this is that low altitude planets end up having their colours smeared in a vertical direction – they then have a noticeable blue fringe at the top and a noticeable red fringe at the bottom. This particular tool amplifies this edge-tinge phenomenon and allows you to clearly see the degree to which you have removed the fringing with the ADC. For more information, I have a dedicated section on my ADC webpage which describes the use of the edge-tinge method to adjust your ADC and the webpage probably tells you more about ADCs than you would ever wish to know.
The edge-tinge tool works by boosting brightness of the planet so the centre of the planet becomes over-saturated and also increasing the image colour saturation. The dialog box for the edge-tinge tool has two different appearances depending on the overexposure method chosen.
The image below shows the dialog box for the ‘Sum of frames’ method which adds frames together to increase the planet brightness. For best performance I would recommend turning the colour saturation up to maximum and summing 5 to 10 frames of the normal exposure.
A variant on this is the exposure factor method which just uses a longer exposure. Again an over-exposure of 5x to 10x your normal ‘correct’ exposure should work well.
A great feature that Torsten has added to this mode, is that overexposed areas are changed from their usual red colour to black eliminating the distracting over-exposed middle of the planet. This makes the tool more sensitive to changes in ADC setting and it is highly recommended to use it.
A word of caution if using this black overexposure feature. If the ADC tuning tool is enabled when imaging with a bright sky background, overexposing the background by 5x-10x may make the whole frame over-exposed – in which case the whole frame will be black! This happened to me and it took me a while to work out what was going on.
The classic ADC tuning mode determines the centre of gravity of the blue image and the red image and displays them together on an XY plot with the overlapping area shown white. The centre if gravity of each image is marked with a cross and the calculated offset in X and Y for each colour relative to the green (green disc not shown for clarity) is displayed in the top left (blue) and top right (red) corners of the tool frame.
The aim with this tool is to adjust the prisms on your ADC to minimise the numbers and make the red and blue disc as coincident as possible.
The dialog box for this tool allows you to average multiple frames to reduce noise and provide some more meaningful mean positions. It also allows you to change the degree of exaggeration of the relative positions of the red and the blue.
This is an evolution of the classic tool with more features added. As well as the items included in the Classic version (except the main cross marking the centre of the green), the Advanced mode includes a red/blue bargraph for the X displacement with respect to green (at top) and Y displacement (just below). It also includes a vertical rolling plot of the blue and red X (?) offset relative to the green. The settings box looks the same as for the Classic tool and the aim is the same to make the red and blue as coincident as possible and minimise the numbers.
In the Outline mode Firecapture estimates the outline of the red and blue image and overlays them relative to the centre of the green (green not shown by default). As with the edge-tinge mode there are no numbers to minimise; here you just adjust your ADC prisms to make the two coloured circles as concentric as possible.
This mode has lots of settings to play with, allowing you to make the overlapping area white and also adding in the outline of the green if you wish. Probably the most useful setting is the B outline size which allows you to increase the relative diameter of the blue circle compared to the red. Boosting the blue to something like 104% makes is simpler to verify the concentricity of the red and the blue circles which otherwise overlap confusingly.
Mini Classic Mode widget
There is an option in the Histogram dialog box, accessible by clicking on the down arrow at the right hand side of the Histogram icon, to add a mini Classic Mode widget to the mini histogram plot. Below you see the widget at the left hand end of the Histogram plot.
The widget is switched on and off in the Histogram dialog box under ‘Show ADC tuning help in histogram panel’
Dummy Cam is a camera emulation mode for helping to understand Firecapture and many of its features without having to connect a real camera to your computer. To start up in Dummy Cam mode, just select it when you open Firecapture with no real camera connected. If you do that this following camera selection box will appear:
Just click on Dummy Cam and Firecapture will open in emulation mod- loading a sample video running in the Preview screen for the currently selected object. In this mode you can play around with many settings to see what they do and even make recordings of the data in the preview window. Certain features do not work properly and the video will not respond to changes in ROI, exposure, gain, colour balance etc.
You can change the dummy cam video by putting your own video in the ‘testImages’ folder in the Firecapture folder (not the User one on the C:drive but the User Space installation). Just change its name to match the existing one in there after renaming the previous one, for example, jup.ser or mars.avi
Not many users know the neat trick that if you drag and drop one of your own videos onto the Preview Screen it will start playing in the Preview Screen.
These sections have yet to be completed but give you an idea of what sections are waiting patiently in line to be written!
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Video Limit Picker
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