Wednesday, August 10, 2011

Gimp and the alpha channel

I was helping MadMike the other night by doing some QA on four engine repaints he did for the LINC. While working through my checklist I kept on looking at how glossy the engines were. This wasn't a grand discovery on my part and has been an on going issue with all of Mike's repaints simply because Gimp does not support alpha layers very well. In this case it was nagging me because another member over at RWA happened to mention it, and it was reverberating in my head while I was looking for other defects. Finally after clearing each engine for repackaging, I loaded the texture up in RsBinTool, exported the DDS over to CS3 and my jaw dropped.

I know that Mike would not have wanted to use a mask for this. I got him on the chat line, and handed him a link to the image above. To say the least he was surprised at seeing the drop out, however it made sense to him. The method he used to create the alpha layer in Gimp can be found here. Where it fell apart was that in Gimp the layer looked fine (the darker gray), so it wasn't obvious that it wasn't working as intended. The good news is that I modified the layer the way Mike wanted it, and he can now duplicate that layer for the rest of his repaints, so this shouldn't be a problem again.

There is another interesting thing I learned from all this. I am probably setting my alpha layer too dark with my own repaints. Generally I set the channel to be completely black, so I get a matte finish on the model, but while I was experimenting with Mike's repaints I began to understand why he had his set to an 80% gray. The slight gloss, almost semi-gloss finish that it gave the model made the colors more believable, and provided another layer of depth for the model (light vs. shadow). I will experiment on some of the repaints I have already released. If the there is a marked improvement then I will consider releasing an update.

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