sturkwurk opened this issue on Dec 19, 2006 · 30 posts
AnAardvark posted Thu, 07 June 2007 at 10:26 AM
Quote - Alpha channels have nothing to do with resolutoin. If you have a more advanced photo editor, you can see channels (usually a red, green, blue channel and an alpha - Alpha are great to use for making image masks)
pngs (sometimes)
psd
tif
formats all can have an alpha channel. Poser 7 is not creating one like it should be if there's a background picture - Poser 6 makes them just fine. (I havent tried tiff yet - but that's a work around I may have to do for now)Doug
Actually P6 was doing them incorrectly. An alpha channel is an associated image where there is a value for each pixel of 0 where there is no image coverage, 1 where the coverage is full, and fractional values where the coverage is partial. In P6, background images were treated essentially as background colors, so the alpha channel ignored them. In P7, they are treated correctly (or at least consistently with other applications), as actual parts of the image. P6 didn't handle alphas correctly. Imagine a half-transparent glass ball rendered without a background. The alpha would have values approaching 1 along the edges of the ball (as seen by the camera), and 0 toward the middle where there is less glass thickness. If I composite the ball with a red background, the ball appears red (with lighter red edges), if against a blue background, it appears blue.
In P6, if you render the ball against a blue background, the alpha channel will be 1 where the b all is and 0 everywhere else, and no matter what background you composite the ball against, the ball will be blue.
Essentially, the P6 alpha channel is just a mat selection of the non-background portions of the scene.