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Transparent overlays

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I''m using Photoshop, and I want to overlay one image with another, where the image on top is 100% transparent for any pixel that is RGB(0,0,0) and 0% transparent for any other pixel. I''d also like to do this in index mode too, where index 0 is 100% transparent, but all other pixels are 0% transparent. Can it be done? This is natural in DX where you have a color key, but I can''t figure it in Photoshop. The transparencies that I figured out make an entire layer transparent by a %, not just one color.

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quote:
Original post by johnny_north
I''m using Photoshop, and I want to overlay one image with another, where the image on top is 100% transparent for any pixel that is RGB(0,0,0) and 0% transparent for any other pixel.

I''d also like to do this in index mode too, where index 0 is 100% transparent, but all other pixels are 0% transparent.

Can it be done? This is natural in DX where you have a color key, but I can''t figure it in Photoshop. The transparencies that I figured out make an entire layer transparent by a %, not just one color.


DX7 can use colorkeying yes, but in DX8 it''s all done with alpha. A 24 bits RGB image has an additional 8 bits to make it 32 bits, the A is between 0..255 and describes how transparent it is. If Photoshop supports it, you should look into alpha values and use the alpha map to paint transparency, this will also make supporting it in DX easier.

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