alpha mapped tgas amplify each other?

Well, I managed to make some neat alpha mapped tgas,…that is until I stack them. They seem to intensify when stacked against each other…? Is there any way to avoid this? Also, is there a way to get a shadow from an alpha mapped plane without getting the transparent portion in?
I tried overlapping a commercially made tga, and this wasn’t a problem. The method I used was to render something on a blue background, then GIMP it and ‘color to alpha’. Any ideas on how to improve my method?

Render directly with an alpha channel…

Change the format to TGA or PNG
Sky-> Keys or Premul (Keys is better)

All those settings are in the Display wndow (F10).


Thanks Theeth I will try that.
<edit> It worked. Thanks again.

meh… Did you have any doubt?



I have been working on making a good alpha mapped tga, and what I found, is that if you make a good one, they require no special settings outside of materials to function adequetly,…I tried several different processes, but for some reason, this is the one that worked:

  1. First I got out Lsystem, and made a bunch of trees and bushes, and rendered them on a solid white background, after adjusting the lighting a bit, and saved as a tga…<edit>>>I forgot to mention, when you save the render leave OSA off! [!] <<<edit>>> blah,…also forgot to mention,…use something other than a white lamp for the render, so photoshop doesn’t confuse your object with the white background>>
  2. Then I went into photoshop, made a new file with a transparent background, and copied the pic onto a new layer.
  3. I used select color range to select the white, and then clear to delete it, then saved as a PSD
  4. Opened up the PSD in GIMP, and exported as tga.

Don’t ask me why,…this just gave me the best result. The tgas I got totally rule. And, no problems with stacking, or backgrounds vs. objects, or anything, in default mode.

Just a quick side-note. If you wanted to save the TGA directly from PhotoShop instead of saving as PSD, then going to the Gimp, you would probably have to do something like this:

  • On the channels/layers dialog select new channel. This will be your alpha channel.
  • With your layer with the image on selected, select the entire contents of the layer. This should select everything that’s not transparent.
  • Switch to the alpha channel so that you can paint on it. It should let you paint as a greyscale. Flood fill your selection with white, leaving the rest black
  • Flatten image
  • Save as 32 bpp TGA

This might not be easier than using the Gimp, but might give you clues as to why TGAs saved from the Gimp had an Alpha channels and those from Photoshop didn’t. I’m assuming that the Gimp must have automatically created an alpha channel from the psd file with transparency.

Edit: You could do something similar to this in the Gimp, if you only wanted to use that