I am trying my hand at astrophotography.

I am using the software Siril on Linux to stack my images. This software uses the .fit file extension (for the FITS format).

It seems to me like FITS is in black and white, and not color. Am I mistaken on this?

Is there a way to preserve color in FITS, or derive it afterwards?


2 Answers 2


Siril has the ability to demosaic the FIT file, there is a checkbox on the file conversion tab. I found it best to de-mosaic the pre-processed / stacked FIT file as a last stage, it speeds the processing up on the intermediate steps as you are working on one layer not 3 (Red Green and Blue).

The siril documentation explains this more fully.

Here's the method that worked for me.

To process a star trail sequence with multiple dark frames in siril.


In File Copnversion tab click change dir and add a working directory eg "siril working dir". Add raw darkframes in file conversion source and then enter sequence name eg darkframes, press convert button. We now have darkframes_seq loaded. In Stacking tab select Stacking Methods > Median Stacking and Normalisation > No normalisation. Then click Start Stacking to create darkframes_stacked.fit


In File Conversion tab clear source with remove all files from list button then add raws to be processed in file conversion source and enter new sequence name eg P6174240-53, press convert. FIT image files are created and sequence P6174240_53_.seq is automatically selected.


In pre-processing click use dark and browse to darkframe_stacked.fit then click Start pre-processing. Pre-processed FIT files prefixed "pp_" created and image sequence pp_P6174240_53_.seq is automatically selected.


In Stacking select Stacking Methods > Pixel Maximum Stacking and click Start Stacking to create the ingle stacked image pp_P6174240-53_stacked.fit.


Check Demosaicing then use Siril Control Center File > Open > pp_P6174240-53_stacked.fit. to carry on in the same window.

In Control Center click Image Processing > Histogram and apply autostretch or alter sliders. Control Center > Image Processing > Remove Green Noise > apply. Control Center > File > Save As > Tiff. Enter file name eg debayered_pp_P6174240-53_stacked.tif and save. Open in Gimp (ideally 2.9x other editors are available) and adjust as necessary (curves / saturation / cloneing) then export.

see https://free-astro.org/index.php/Siril:Manual and https://free-astro.org/siril_doc-en/#Reference_documentation_1


No, FIT can store color photos (even X-Ray and infrared data :) ). SIRIL uses unsigned 16-bit per channel values (TUSHORT), and images are stored channel after channel on a bottom-to-top, left-to-right order.

I think you have to open your FIT files in another program. GIMP, Photoshop and Irfan cannot show full image and, perhabs, colors, so I recommend you to use FV.


Screenshot of FV:

enter image description here

  • \$\begingroup\$ Ok, so once I have my finished stacked .fit image, what do I use to convert it to a conventional color image format? \$\endgroup\$
    – Scorb
    Nov 26, 2017 at 20:38
  • \$\begingroup\$ FV can edit an convert your FIT files to JPG or BMP. Try to open and see store store Siril color components or not. \$\endgroup\$ Nov 27, 2017 at 1:32
  • \$\begingroup\$ So sigil will happily convert your images to fits format, but provides no facility to convert back? \$\endgroup\$
    – Scorb
    Nov 27, 2017 at 2:27
  • \$\begingroup\$ FV does not offer and export or convert feature. It doesn't even display the image. \$\endgroup\$
    – Scorb
    Nov 29, 2017 at 1:54
  • \$\begingroup\$ See my updated answer: here is screenshot of working FV with sample FIT-file. Possible you cannot convert image to JPG due to you have not installed additional viewer as described in Help. \$\endgroup\$ Nov 29, 2017 at 3:33

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