How do I make the alpha channel more opaque?

I am dealing with a game texture. The alpha channel determines the smoothness.

I would like to paint the alpha channel (make it opaque or transparent) in GIMP.

I have clicked the alpha channel in the Layer tab.

When I select a brush, select White and paint, the checkerboard shows up more:

However, when I paint with Black to make the alpha channel opaque, nothing happens.

What am I doing wrong?

Thank you.

Yes, you are doing it wrong. When you enable/disable a channel in the Channels tab, you make it sensitive to paint operations. But when you paint with the brush on a transparent area the value of the alpha channel (or more accurately the opacity of the brush) is always 100% .

If you want to paint the alpha-channel, you have to use "layer masks":

• Layer > Mask > Add layer mask to add a mask (in your case you probably want to initialize with "Transfer layer's alpha channel"
• On the status bar at the bottom if the image, the layer name is now "{name of layer} mask"
• You also have a thumbnail of the mask next to the layer thumbnail in the Layers list.
• Paint on the mask (black is transparent, white is opaque)
• You can switch from painting RGB or Alpha channel by clicking the layer or mask thumbnail in the Layers list.
• Possibly Layer > Mask > Apply layer mask when done (but you should be able to export the image directly, this will apply the mask)