Re: [Gimp-developer] Overlay Mode - fix.

["Guillermo Espertino (Gez)" <gespertino gmail com>]

El 13/11/12 14:37, Michael Natterer escribió:
> The problem is much bigger. Almost *all* of our layer modes
> will be "Legacy", and the new modes will operate in linear
> light. Just adding a hack for overlay is not going to
> fix the root problem.
>
> --mitch

Apart from the different overlay formula and all being blended in linear 
light, is there any other layer mode that changes?
I was thinking about the simplest way to tackle this problem, and if 
those are the only differences this might work:

If the file was created with 2.8 or earlier, show a warning and offer 
opening the file anyway or using the legacy mode. If the user chooses 
legacy:
- Promote the file to high bit depth.
- open it normally (afaik this would convert the colorspace to the 
working space and linearize every layer)
- add a gamma correction operation to all the layers applying the sRGB 
TRC (1D LUTs?)
- blend
- Linearize the composite prior the last color-management op.

- Regarding the Overlay operation: Just replace it using the soft light 
mode instead. Correct me if I'm wrong, but in GIMP 2.8 and previous 
versions both modes seem to provide the same result.

Probably applying gamma correction to inputs that were linearized from a 
gamma corrected source sounds redundant, but this is supposed to be a 
legacy mode, a compatibility layer, so the reduced efficiency would be 
probably justified.

If this is possible, switching from legacy to the new native linear 
blending would mean just bypassing the gamma correction nodes.

I'm not a coder and I don't know anything about the GIMP/GEGL internals, 
so I tried using the logic I'd use with a compositing software.
If this is a stupid oversimplification you're entitled to make me STFU :-)

Gez