Option NOT to multiply zero alpha over RGB

[kirk23]

I often  need to work with tga files and Affinty   always mess them  at open stage doing black wholes in RGB channels where Alpha is zero.

When you save tga there is at least an option to add to alpha some 0.0001  with procedural filter  that lets to avoid it  but when yu open the file  it's inevitable.    Can we have an option in the settings somewhere to NOT doing this please. 

[NotMyFault]

Pedanterie Mode:

Affinity does not use premultiplied alpha, except the file format mandates such a format (I don’t know any).

It only erases RGB values to zero whenever alpha gets to 0.

And you probably know the workarounds.

Instead of PT filter you can use any of channel mixer, levels adjustment, or curves adjustment.

[kirk23]

12 hours ago, NotMyFault said:

It only erases RGB values to zero whenever alpha gets to 0.

Thank you  NotMyFault.   I didn't know about background trick  but it still doesn't help me much   since I want  tga  or tiff or exr as linked image from which   I could have an access to each individual channel to use them for masking .   Like 4 masks  from cryptomatte  I packed  in one RGBA output file in Blender compositing  to be then accessible  in Affinity with procedural filter.      Do you know a trick how to do it with PF  so we could use same linked image  as a masks source   without doing  black holes in RGB ?

Works with 3 masks packed perfectly well but the alpha one spoils it .

[NotMyFault]

You can access any channel of an RGBA pixel layer individually and convert it into a color or alpha channel.

the channels panels does this „destructively“ by writing the data from a source channel to either spare channel or selected color / alpha channel of another layer.

The color mixer channel allows to mix channels freely and non-destructively, i use it a lot for this purpose.

there are some principal limitations which cannot be overruled at this time in Affinity apps:

• When you have layers atop of each other in layer stack, then layer blending will apply,
  • you must choose one of the pre-defined blend modes, no option to define blend modes on your own
  • you can choose blend gamma 
  • the equations filter allows to define own blend Formulars, but it is destructive only.
• The alpha channel is always treated differently in multiple aspects, e.g.
  • Zero values in alpha will zero out RGB channels, too
  • alpha blending cannot be adjusted in any way. Blend modes will modify mixing of RGB values, but except erase blend mode all other will mix upper and lower level based on alpha.
  • Alpha channel does not use gamma correction, whereas RGB/8 and RGB/16 will always use gamma corrected blending. But you can adjust blend gamma from default 2.2 to 1.0 so all channels use same gamma.
  • The blend profiles in blend options are the only exception (this is a bug) and use gamma correction by mistake.
• when you want to use alpha aware adjustments like channel mixer, levels adjustment, curves adjustment, there are multiple unfixed bugs since years, e.g. currently a nested levels adjustment does not work correctly on alpha channel 

so it is a game of lots of experimenting what works in Affinity and what does not work.

As long as you are able to keep the layer structure very simple, you have a good chance.

[kirk23]

Thanks NotMyFault