Re: [Gimp-developer] bug when trying to edit color channels of a transparent image

[Ofnuts <ofnuts gmx com>]

On 01/27/18 22:41, Tcll wrote:
> the issue here is when opening a transparent image, the color channels
> don't show the full color info, see here:
> https://cdn.discordapp.com/attachments/98580359909773312/406830380180570113/unknown.png

The RGBA channels at the top are not the channels of a specific layer, 
but the channels of the final composite image. So while the behavior may 
not be what you expect it could still be correct.
> here's the very same PNG opened in MS Paint: (expected when hiding the
> alpha channel)
> https://cdn.discordapp.com/attachments/98580359909773312/406830457083133952/Pikachu_eyesYellow.00c.png
>
> if everything was correct, the color channels would display the yellow and
> red around the eye.
> just because the image is transparent doesn't mean the colors don't affect
> the model it's applied to.
>
> but what's even more of an issue is I'm trying to edit out the red circle
> as I want what's hidden to be fully yellow,
> but the only way I can seem to achieve that is to pull the alpha channel
> from the image and make the image fully opaque before editing the colors as
> hiding the alpha channel makes the entire image transparent.
>
> getting the alpha channel seems to be anything but easy as well as hiding
> the RGB channels makes the entire image black, rather than just displaying
> the alpha mask between black and white.

The canonical way of editing the alpha channel of a layer is to use a 
layer mask. Here is a good tutorial on the subject:

https://patdavid.net/2011/10/getting-around-in-gimp-layer-masks.html