Problem on opening a fit file created by SIRIL

[soulearth]

Hi,

I stacked my astrophoto with SIRIL and save un fit file. I have a problem opening these fit files in affinity photo. The colors are too pale.

In attachment, the same photo in SIRIL, Gimp and affinity and the original file. You will be able to see that there is a problem with affinity.

Can you help me ?

Thank you in advance,

Best regards,

 

resultat_stretch.fitresultat_stretch.fitrresultat_stretch.fitresultat_stretch.fitresultat_stretch.fitresultat_stretch.fitresultat_stretch.fitresultat_stretch.fitresultat_stretch.fitresultat_stretch.fitresultat_stretch.fitresultat_stretch.fitresultat_stretch.fitresultat_stretch.fitresultat_stretch.fitresultat_stretch.fitresultat_stretch.fitresultat_stretch.fitresultat_stretch.fitresultat_stretch.fitresultat_stretch.fitesultat_stretch.fitresultat_stretch.fitresultat_stretch.fitresultat_stretch.fit

 

resultat_stretch.fit

Edited December 17, 2021 by soulearth

[James Ritson]

Hi @soulearth, there isn't a problem with Affinity Photo—rather, there are two things that are contributing to your FIT file appearing brighter and washed out:

1. When opening FIT files, Affinity Photo automatically adds a gamma transform and tone curve as non-destructive adjustment layers. These can be disabled or deleted and you can add your own adjustments for tone stretching.
2. GIMP and SIRIL are showing you the linear colour values with no colour management applied. With 32-bit linear documents, Affinity Photo will non-destructively add a view transform so that your document view is gamma corrected and colour managed (sRGB by default). If you go to your 32-bit Preview panel (View>Studio>32-bit Preview if it is not already present in the bottom right), you can switch from 'ICC Display Transform' to 'Unmanaged' and then your image will appear consistent when compared with what you are seeing in GIMP and SIRIL (assuming you have already disabled the Levels and Curves adjustments).

Be aware, however, that you should always be using 'ICC Display Transform', otherwise your editing view will not match the exported result (when exporting to 8-bit or 16-bit JPEG/TIFF etc). The reason Affinity Photo does this, rather than just show you the linear unmanaged colour values, is that you can freely edit in 32-bit and then not have to do any tone mapping or adaptation when converting or exporting to 16-bit/8-bit bounded formats.

To clarify, your pixel colour values are still linear, and all operations in 32-bit are performed in linear space. A final, non-destructive view transform is applied based on the document colour profile (e.g. sRGB) and the final image you see as your view is gamma-corrected. When you change from 'ICC Display Transform' to 'Unmanaged', you disable this view transform, enabling you to see the linear colour values. This is however just intended as a preview capability, and will not affect the exported result.

Hope the above helps!