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alphagimp

GIMP packing image into alpha (pasting grey scale image into alpha)

Trying to do an optimizing trick called channel packing

My image doesnt actually use an alpha layer. So i add one then take a grey scale image I have for roughness inside of a game engine and put it there. Within the engine this is now only one texture but i can plug the RGB into the base and alpha into roughness.

How do I do this? I figured out how to add an alpha channel but it doesnt let me just paste a grey scale image into the channel.

Appreciate the help!

Solution

  • Method #1

    • Add a layer mask Layer>Mask>Add layer mask
    • This automatically selects the mask as the target of editing (in the bottom of the image displays, it says {layer name} mask.
    • Paste your image (Ctrl-V). This creates a floating selection, which is a layer, but don't worry. You can see that this layer is impacting the opacity of the layer below, which is a hint that it really applies to the mask. You can move that layer if you need to adjust the position of the paste.
    • Layer>Anchor layer (Ctrl-H) and your temporary layer is pasted over the mask.
    • Layer>Mask>Apply layer mask to "commit" the changes.

    Method #2:

    • Paste your image and make it a new layer (Ctrl-V, Ctrl-Shift-N)
    • In the Channels list, drag any of the R,G,B channels to the list below to copy it.
    • Remove the pasted layer, select your target layer
    • Layer>Mask>Add layer mask, initialize to a channel, and select the channel you created above.
    • Layer>Mask>Apply layer mask to "commit" the changes.