Chaky

Thing is, the alpha channel is used as specular highlight map. Only the blue channel (to my understanding) is unused. I guess the normalmaps must not be resized using any other method than "Nearest neighbour". I wish I knew that before edited tonnes of normal maps that were missing mipmaps...

Whether the alpha is 0 or 255 when the pixel is completely transparent, I don't know. Yes, it matters if the dds file is normal map. It is actually ruining the texture. When displaying the picture, it can not represent the transparent pixels. But that does not mean that R, G and B channels should be all set to 0. Alpha channel is separate from RGB channels, and they must not get altered with alpha. The "other tool" is bug-infested allright, but that's beside the point. It does not matter how the other tool represents the alpha channel. Actually, it completely ignores the alpha when previewing the picture and display RGB part only. That is why there is virtually no difference between wall01 and wall02, and that's how one can see that Paint.NET is actually destroying the RGB channels when resizing, and not during the actual editing. I remind you that wall02.dds contains RGB channels intact WITH the srike of alpha across the picture. Wall03.dds is the outcome of resizing of wall02.dds. Not the eraser.

Here's the example. There are 6 files within the archive. 3 dds files are examples I just made, and 3 jpg files are screenshots of those files without an alpha channel, viewed from another tool. wall01.dds is the original wall02.dds is that same original with a stroke of eraser across the picture. As you can see, the picture is still preserved. Only alpha channel is added. wall03.dds is wall02.dds, but resized (to 1024x1024, then back to 512x512). You can see that the transparent part is now black. Edit: It is done with Paint.NET. Only the 100% transparent pixels are turned black, so it is impossible to see from within the Paint.NET. This doesn't happen when "Nearest Neighbour" method is used when resizing (or generating mipmaps). Examples.7z

Whenever the picture is resized by using other than "Nearest Neighbour" method, and if alpha channel is present, the all-transparent parts actually become black. It affects image resizing and mipmap generating. I guess the culprit is in the resizing code. Apparently when alpha channel is 255, Red Green and Blue channels are set to 0. Only the "Nearest neighbour" method doesn't produce the black spots. I'm using Paint.NET to work with textures (including normal maps with embedded mipmaps), and changing colors to black is very unwanted effect.