Moving an alpha channel, & keeping file untagged with colour space

[KayL]

I have been using Photoshop (PS) to tweak 'raw' film scan TIFFs from Vuescan (64-bit RGBI). Some of my scanners use 2-pass for the infrared dust alpha channel, and the registration with the RGB layers is occasionally off. I sometimes move the alpha channel in PS, and resave the file prior to Vuescan reprocessing (which requires no ICC profile to be associated with the TIF file). It takes a minute or less in PS. (Channels -> Move Tool -> Save)

I tried doing the same thing with Affinity Photo (AP), and can't figure out how to do it. AP forces me to apply the working colour space to the file, and the 'channels' tab doesn't let me move the alpha channel like a layer.

I'm curious as to whether AP can actually do this, or whether it's beyond its feature set. I'm currently on V1.9.1.

[NotMyFault]

Hi KayL,

your issue regarding edit of alpha channel has been discussed (partially heated) in many posts of this forum.

Affinity Photo differs strongly to PS in handling of alpha channel.

You cannot directly edit the alpha channel in the same way as a RGB channel.

But you can easily swap the alpha channel into an regular RGB channel (of a new pixel layer), edit it there, and then load it back into the alpha channel of the original layer.

Using the channels panel, when your pixel layer is active and selected:

1. In Channels panel, at "Pixel Alpha", rigth-mouse-click, Create Grayscale Layer.
2. You get a new grayscale pixel layer you can edit.
3. When finished, In Channels panel, at "Pixel Red", rigth-mouse-click, Create Spare Channel
4. Select your original layer again
5. In Channels panel, at "Spare Channel", rigth-mouse-click, "Load to Pixel Alpha

Regards,Timo

[KayL]

Thank you for your clear and concise reply. I conducted a search prior to this posting, and saw the other heated forum discussion thread. Unfortunately I wasn't able to locate the salient information amongst the noise.

Any advice on working with/saving a file with no colour space tagging would also be welcome. A previous forum search was unfruitful.

Edited March 5, 2021 by KayL

[NotMyFault]

Hi,

have a look at Color Profiles help pages:

https://affinity.help/photo/en-US.lproj/pages/Clr/ClrProfiles.html

To convert the color space of file to be opened to the current working space:

• Prior to opening the file, from Edit>Preferences, check the Convert opened files to working space option.

Options exist to warn that a file's working space will be converted, or that an unprofiled file will be assigned the current working space's profile.

 

But it seems there is a open bug in Photo, thus never warn when opening, and possibly always attaching a profile when saving:

For exporting, you have the option to not attach a color profile, and this at least seems to work for jpeg.

I have no untagged TIFF file to check, can you please provide a sample (please zipped before upload to avoid modifications by the forums upload software)?

 

[KayL]

I've decided that Affinity Photo is not the right tool for this use-case, based upon your suggestions and subsequent practical testing.

Thank you very much for your assistance.