Frequently Asked Questions

Light, Dark, Flat, Bias... What are they and how to create them?
Files and File Lists

The downloaded setup files are corrupt.
The executable files on github are definitely OK.  It's possible that you are using a download accelerator.
If so, I suggest you deactivate it, and download the file again and all should be ok.

When I try to run DeepSkyStacker after I have installed it I get a message: "This program can't start because api-ms-win-crt-runtime-l1-1-0.dll is missing".
Your need to install that DLL file which you can download from: 
you will need to download the version specific to your version of 

Light, Dark, Flat, Bias... What are they and how to create them?
(if you are wondering how all the files are used during the calibration process you can have a look here)

Light Frames
The Light Frames are the images that contains the real information: images of galaxies, nebula...
This is what you want to stack.

Dark Frames and Dark Flat Frames
The Dark Frames are used to remove the dark signal from the light frames (or the flat frames for the Dark Flat frames).
With DSLRs and CCD Camera, the CMOS or CCD is generating a dark signal depending of the exposure time, temperature and ISO speed (DSLR only).
To remove the dark signal from the light frames you use a dark frame that contains only the dark signal.

The best way to create the dark frames is to shoot pictures in the dark (hence the name) by covering the lens.
The dark frames must be created with the exposure time, temperature and ISO speed of the light frames (resp. flat frames).
Since the temperature is important try to shoot dark frames at the end or during your imaging session.

Take a few of them (between 10 and 20 is usually enough). DeepSkyStacker will combine them automatically to create and use a clean master dark or master dark flat.

Bias Frames (aka Offset Frames)
The Bias/Offset Frames are used to remove the CCD or CMOS chip readout signal from the light frames.
Each CCD or CMOS chip is generating a readout signal which is a signal created by the electronic just by reading the content of the chip.

It's very easy to create bias/offset frames: just take the shortest possible exposure (it may be 1/4000s or 1/8000s depending on your camera) in the dark by covering the lens.
The bias frames must be create with the ISO speed of the light frames. The temperature is not important.

Take a few of them (between 10 and 20 is usually enough). DeepSkyStacker will combine them automatically to create and use a clean master bias/offset frame

Flat Frames
The Flat Frames are used to correct the vignetting and uneven field illumination created by dust or smudges in your optical train.

To create good flat frames it is very important to not remove your camera from your telescope before taking them (including not changing the focus).
You can use a lot of different methods (including using a flatbox) but I found that the simplest way is to put a white T shirt in front of your telescope and  smooth out the folds. Then shoot something luminous (a flash, a bright white light, the sky at dawn...) and let the camera decide of the exposure time (Av mode),

The flat frames should be created with the ISO speed of the light frames. The temperature is not important.

Take a few of them (between 10 and 20 is usually enough). DeepSkyStacker will combine them automatically to create and use a clean master flat frame.

Is it possible to use colored flat frames?
The short answer is yes.
The overall tint of your flat frames is not really important because DeepSkyStacker is processing each channel separately and is applying the flat frames to each channel accordingly.
Of course if your flat frames are fully red only the red channel of your light frames will be properly calibrated but otherwise as long as as the peak in each channel is between 1/3 and 2/3 of the maximum you should have no problem using slightly colored flat frames.

Files and File Lists
DSS can't read my TIFF files and/or crash when trying to read TIFF files
DeepSkyStacker is only supporting uncompressed TIFF files or LZW and ZIP (Deflate) compressed files.
However, TIFF files come in many flavours and sometimes the decoding may go wrong especially while decoding EXIF information.
It is possible to disable EXIF decoding when reading TIFF files by adding the following registry key under HKEY_CURRENT_USER\Software\DeepSkyStacker: SkipTIFFExifInfo (DWORD) with a value of 1.

If you don't know how to add the registry key, you can download this small file and double-click on it. It will add the registry key for you.

My FITS files are not correctly decoded.
There is a lot a FITS file format out there..
If your FITS file is not correctly decoded please send me an email with the FITS file attached.

My FITS Files were created from a DSLR and are very dark and without any contrast.
Software capturing DSLR output and storing them as FITS files sometimes use the 16 bit file format to store only 12 bit depth images (which is the original depth of most DSLR's RAW files).
In this case the values stored in the files are between 0 and 4095 instead of between 0 and 65535 which explains why the images are very dark.
You can adjust the parameters in the FITS Files tab in the RAW/FITS DDP settings dialog to correctly see these files.
Simply put you can multiply the total brightness by up to 16 without exceeding the maximum threshold. If you modify the white balance by changing the red and/or blue scales take care not to go over that 16 multiplier for each channel (brightness * channel scale).

My FITS Files were created from a DSLR and appear all wrong while I have selected the correct DSLR in the FITS File tab
You should check that no binning was used by the software making the captures. In this case DSS can not use the standard Bayer Filter Pattern of your DSLR and this is probably why your images appear all wrong.
The only way is to deactivate binning.

My FITS files were create by a color CCD camera and I see only B&W images.
Your FITS files are using a bayer matrix (like a DSLR). To decode the colors correctly DeepSkyStacker must know which kind of Bayer matrix is used by your camera..
You can use the FITS tab of the RAW/FITS DDP settings dialog to tell DeepSkyStacker which Bayer matrix must be used. Most of the time you will just have to select your CCD camera from the list.

What is a File List?
A File List is just a plain text file containing file names with, for each file, its type (light, dark, flat, offset) and its status (checked or unchecked).
You should note that when a File List is loaded the list containing all the files is not cleared.
Thus it is possible to have a File List with all the dark frames, another with the flat frames, a third with the master offset and to load all the File Lists in one operation.
The File List format is fully explained here.

I have files of the same object taken in multiple imaging sessions. How do I tell DSS to associate correctly the dark with the light frames of the same night for each night?
The answer to this question is to use File Groups.

Why create a registering file for each picture?
Because it is simpler and it avoids re-registering.
This is also a way to avoid loading all the pictures during the registering and stacking processes.

Can I delete the registering file?
Yes. It will be recreated if necessary.

Can I modify the content of the registering file?
Yes, even if it is neither advised nor necessary.
I cannot guarantee that the content will not evolve, but I guarantee that the current content will always be decoded.

What is the score, and what is its meaning?
The score is a measure of the picture quality.
To put it simply, the higher the score, the more round and not too big stars were found.

Is the score a measure of the absolute quality of a picture?
No. The score is a relative measure that is only used to sort the pictures of roughly the same area in order to keep only the best pictures for stacking.
If the raw development process settings are modified you must register the pictures again and a new score will be computed.

What is the AutoSave.DSImage file created after each stacking process?
The AutoSave.DSImage file is a proprietary file which is created automatically at the end of each stacking process and that holds the resulting picture. It is a 32 bit (rational)/channel format.
Since the only way to create this file is to do a new stacking process it is not possible to overwrite it by mistake.
It can be reopen in the processing tab.
Starting with the 2.5.3 release the AutoSave.DSImage file is replaced by an AutoSave.tif file which is a 32 bit rational TIFF file (Deflate compressed).
Older .DSImage files can still be opened by DeepSkyStacker.

The resulting image shows multiple sets of stars on all the picture
Multiple sets of stars is a sure sign that the alignment process is relying on "false" stars.
The main reason is that hot pixels are perturbing the registering process and thus are creating false stars.
You can try to automatically detect hot pixels (see Registering Options) or, much better, load and check your dark frames before starting the registering process.
All checked dark, flat and offsets frames will be applied to each light frame before the registering process guaranteeing that no hot pixels or artefact will perturb the star detection which will be much better and accurate.

The resulting image shows a heavily cropped image in the upper left corner
This is the result of registering the light frames using the super pixel mode and stacking them in another mode.
When changing from or to the super pixel mode it is necessary to register the light frames again.

My dark frames have not all the same exposure time and DeepSkyStacker does not group them together.
If you don't use an automatic way to take each frame it is often possible that the exposure times are different by a few seconds and in this case DeepSkyStacker does not group them together to create master dark.
You can force the exposure time for each frame to the same value by selecting the frames in the list an by using the context menu to edit the properties of the frames.

My resulting image is very dark. Is it normal?
RAW images are very dark and stacking them create a very dark resulting image.
To view the details in the image the histogram must be stretched by adjusting the RGB levels and the luminance in the Processing Tab.

How do I align the resulting images of 4 stacks (red, green, blue and luminance)?
To align the resulting images on the same reference frame just add the reference frame to the list even if it is not from the same stack, force DeepSkyStacker to use it as the reference frame (using the context menu) but left it unchecked.
This tells DeepSkyStacker to use it as the reference frame but to not add it to the stack.

What is the DSSSettings.DSSSettings file created in the DeepSkyStacker.exe folder?
The DSSSettings.DSSSettings file contains all the adjustment settings that can be saved and loaded from the processing tab.

How to speed up stacking
Besides the obvious answers (faster processor, more memory), the best way to speed up processing is to use the non interpolation modes (Bayer Drizzle and Super Pixel) or the bilinear and AHD interpolations which are all working only on the raw files with only one monochrome 16 bits channel instead of 3 RGB channels.
The picture decoding is faster (fast or no interpolation), the required memory is divided by 3 and flat, dark and offset frames are computed and internally stored with only one plane instead of 3.

Another way to get the resulting image faster is to use a Custom Rectangle which contains only the interesting part of the image.

Where are saved the post-processing adjustments settings in the TIFF files?
The settings are stored as private TIFF tags. It is a documented feature of the TIFF file format.
On the other hand if you overwrite the file with software other than DeepSkyStacker, the private tags will be removed and the settings will be lost.

What is the difference between applied adjustment settings and embedded adjustments settings in the TIFF file?
When the adjustment settings are embedded the picture stored in the TIFF file is the picture without any modification as it results from the stacking process. The settings are included so that the next times you open the TIFF file in DeepSkyStacker you can continue to work from where you stopped.
This option is useful if you want to continue to post-processing later using DeepSkyStacker or if you want to do all the post-processing with another software.

When the adjustment settings are applied, the picture stored in the TIFF file is the one resulting from applying the settings to the picture resulting from the stacking process. It is the picture as you see it in the processing tab.

Photoshop can not open the 32 bit (integer) TIFF files created by DeepSkyStacker?
Right, You must save the file in 32 bit (rational) TIFF file format to open them later in Photoshop.
Software like Pleiadesí PixInsight can open 32 bit (integer) TIFF files created by DeepSkyStacker.

Does DeepSkyStacker use the registry to store settings?
Yes. DeepSkyStacker is storing all the settings associated with the user in the registry database: last folders for each kind of file, last dialog settings...
Everything is stored in the HKEY_CURRENT_USER\Software\DeepSkyStacker key.

Why DeepSkyStacker?
Simply because spending countless hours repeating the same tasks other and other for each new set of pictures has stopped appealing to me.
Every owner of a DSLR will understand what I am talking about: TIFF transform (or CFA for the bravest), registering, stacking...

After testing a lot of memory hungry software I decided to write the software that will solve my problem: getting a whole set of pictures (sometimes several hundreds) and doing all the process automatically so that I can go to sleep knowing that the following morning I can start the post-processing which is the fun part.

Why not planetary pictures?
Why? Because I don't do planetary so I have no experience and I wouldn't know where to begin.
Maybe one day I will find an interest in it and I will write a PlanetaryStacker ... but don't count on it anytime soon.

And DeepSkyStacker 1.0?
DeepSkyStacker 1.0 was only used by me and some close friends. It was not intended to go public and even if the engine was already there a lot a features were missing.
DeepSkyStacker 2.0 is the first public release.

In what language DeepSkyStacker is coded?
DeepSkyStacker is coded in C++.

How are Camara RAW files decoded?
The RAW files are decoded using LibRaw  Copyright © 2008-2019 LibRaw LLC, which is the successor to the superb DCRAW decoder written by Dave Coffin.
Thanks are due to Dave Coffin for suggesting to Luc Coiffier the Bayer Drizzle algorithm.

Is my DSLR file format supported?
The list of all the DSLRs supported (presently more than 300) is increasing all the time. Go to the LibRaw website to know if your DSLR is supported.
DeepSkyStacker will warn you if your DSLR is not supported in the current release.

How are read and written the TIFF pictures?
The TIFF files are read and written using the most excellent libtiff library

How are read and written the FITS files?
The FITS files are read using the most excellent CFitsIO library

Is it possible to change the language used by DeepSkyStacker?
The language used by DeepSkyStacker (French, English, Spanish, Czech, Italian, Catalan, German or Dutch) is automatically set from the language used in the Operating System.
If you want to force another language you can change it from the About box.
DeepSkyStacker must be started again for the new language setting to be effective.

How DeepSkyStacker checks that a new version is available?
To check that a new version is available DeepSkyStacker connects to the website at startup and compare the currently used version with the downloadable version.
DeepSkyStacker does not send any personal information to the website or anywhere else during this process. It just downloads a very small file containing the necessary information.

Is DeepSkyStacker Open Source? Is the source code available?
Yes, DeepSkyStacker has been Open Source since 2018.  The DeepSkyStacker Project is stored on github.

How do I uninstall DeepSkyStacker?
Simply use the uninstaller from the Add/Remove programs in the control panel.