11-29-2022, 02:04 PM (This post was last modified: 11-29-2022, 02:09 PM by leiopar.)
I use GIMP since the first version 2.
I noticed recently a change in the behavior of the "color to alpha" command from the 2.6 vertion. When I want to extract the white from a layer, the result is too pale when we put it over a white layer (which should however visually cancel the transparency effect)
See attached file : http://leiopar.free.fr/DISKETTE/gimp_cou..._alpha.zip
I asked the question here, with no results.
Please, how to reproduce the behavior of GIMP 2.6 with GIMP 2.10 ? (it is now not found in portable vertion)
Bucket fill with the bucket tool in Color Erase mode (and with the color to erase of course). This is the best way in 2.10 to get the exact erasure (in other words if you put the result over a background of the erased color, you get back exactly the initial image).
In case you wonder, one thing that changes in 2.10 is that now all computations are done in "linear light". Up to Gimp 2.8, channel values where gamma-encoded and computations were done directly on these values (which is conceptually wrong). A well known result was the red-to-green gradient that goes through brown instead of going through orange but this had other implications such as computing the correct composition of semi-transparent pixels.
Since I installed a Gimp 2.6, I made a 2.6 xcf file to play with (attached for info)
Open in Gimp 2.10 and it is in legacy mode.
Leave it in legacy mode and color-to-alpha (c2a) which is now a GEGL procedure works as in Gimp 2.6 https://i.imgur.com/cQYOBxx.jpg
Change the mode to default, there are good reasons for the enhanced Gimp 2.10 color options, apply c2a and get that faded effect. https://i.imgur.com/BIpYGR9.jpg
It is possible to get close to the legacy version by reducing the opacity threshold, say 0.5, not quite an exact match, needs a little more transparency. https://i.imgur.com/Ldln5jA.jpg
