Is this meant to work? Layer Mask on Decomposed image

[JonLang]

New Image.

Right click image, colours > Components > Decompose

RGB > Ok.

Add layermask to each layer (Shift click)

Pencil in white on the layermasks to what is wanted

Right click image, colours > Components > Recompose

The image does not take the layermasks.


This is also the case when right clicking the layer and 'Apply layer mask' the recompose

Thanks

Jon

[rich2005]

Is it meant to work ? Probably not

I think it is because using a layer mask is introducing areas of transparency into what is already a greyscale mask.

1. Decomposed, with layer masks and 'penciled' in on layer masks. https://i.imgur.com/hHP0pJx.jpg
2. Layer masks applied, gives areas of transparency. https://i.imgur.com/OaCBqkn.jpg
3. Alpha channel removed from each layer. https://i.imgur.com/fvjWrsE.jpg
You might as well just paint on the layer.
4. Recomposed https://i.imgur.com/F8trJLY.jpg

If you can give details of the purpose of the exercise, maybe someone can give some advice / alternatives.

[JonLang]

Thanks for your detailed answer.

I am trying to produce 'SpecMaps' for a cars livery in iRacing. https://www.iracing.com/painttextures/

It takes the Red value of a pixel and makes the pixel on the car metallic between 0 and 255
It takes the Green value of a pixel and adds roughness between 0 and 255
It ignores blue

https://i.imgur.com/s3AdThB.png

In photoshop it seems possible to take these and only 'paint' an individual colour from each layer/ group, I'm looking for the best way to do so in Gimp.

[rich2005]

You need a games user (which is not me) so keep visiting in the hope that one turns up.

I did look at the game site and their screenshot of editing a psd file. Not a lot of use for Gimp. Post that, or part of it, with all the layers as a Gimp xcf file, someone might sort it out.

screenshots: https://i.imgur.com/ef8synO.jpg
Looking at your screenshot, white shapes on transparent background to adjust ? Is that correct ?
The RGB channels in Gimp can be edited and [u[might[/u] be a partial edit.
This a starting out made-up image (1) showing the channels dock (2) and the image decomposed (3) to show equivalence.. Dont be put off by my Gimp, the default black theme and cluttered layout does nothing for me. It is a Gimp 2.10.20

from website quote...Our PBR spec maps use 3 different greyscale maps, Metallic, Roughness, and an Alpha map used to mask out lighting effects To keep from having to have 3 different tga files to represent this, we instead use the RGBA channels in the TGA to house all 3 textures in one file.

screenshots: https://i.imgur.com/KW2AZX1.jpg
quote...Metallic: This greyscale texture tells the sim if the pixel is metallic or not, or something in-between. If the pixel is metallic, then you use white (255,255,255 rgb). If the pixel is non metallic you use black (0,0,0 rgb). Typically, this is a yes or no question...

The shapes can be isolated by selection. Easiest way is Layer -> Transparency -> Alpha to Selection With the red channel active, painted in or out, black or white. (4)

quote...The roughness channel tells the sim how rough the surface of the object is. white (255, 255, 255 rgb) is very rough, and therefore isn’t very reflective. Black (0,0,0) is totally smooth and therefore very reflective. This channel replaces the green channel in our spec maps

Some grey value painted in ? With the green channel active paint in the selections with your value. (5)

screenshots: https://i.imgur.com/vJXqXMG.jpg
With the selection off, the image / layers / channels looks like (6)
Exporting to a .tga file and going back to the title, decomposing that image gives the same as the edited image (7). Might / might not work, I have seen reports the Gimp 2.10 TGA export is not 100%.

best of luck.