Astrophoto Linear format

[Morten Lerager]

Hi all and @James Ritson

It seems like I can import a linear fit into AP.

I want to work with it in a linear state. How can I

export it, still in linear state, for further work and before GHS in Pixinsight.

Thank You.

[James Ritson]

Hey @Morten Lerager, you can indeed import FIT files into Affinity Photo and it will open them in a linear 32-bit pixel format. The data and compositing is actually linear, but there are a couple of things to note:

• A gamma-corrected view transform is applied (but only to the view, not the actual document pixel values) so that the result on-screen looks consistent with a final export to a gamma-encoded format such as JPEG.
• Levels and Curves adjustment layers are added by default for basic tone stretching. You can hide or delete these.

To go back to a linear format, Photo does offer the ability to save as a 32-bit TIFF. Alternatively, you can use JPEG-XL, OpenEXR or Radiance HDR (not sure if PixInsight supports these).

I'm not sure how inserting Affinity Photo into a PixInsight workflow pre-tone-stretch would be beneficial though—wouldn't you just tone stretch in PixInsight then export to Photo for further editing? It may be worth pointing out that you can achieve all manner of tone stretching methods in Photo, they're just not readily available as easy filters that you can apply. Some of them (e.g. colour preserving tone stretch, similar to Arcsinh) are implemented via macros which you can download.

Hope the above helps!

[Morten Lerager]

Thank you @James Ritson

I know all your macro, great work !

You suggest to export i 32bit tiff. That's exactly what i trying to do.

But it seems like any setting, will open in pixinsight, as non linear ( as displayed in AP)

It should be as dark, as if left Pixinsight.

In AP, when exporting i can't get the preview dark. ?

Another way to approach it. :

Pixinsight export a linear fit.

AP import the fit > export as 32bit tif

Pixinsight open the tif. This is giving me at total diff. picture. Lighter not pitch black.

Hope you are able to understand my bad English