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| RLECOMP(1) | FreeBSD General Commands Manual | RLECOMP(1) |
NAME
rlecomp - Digital image compositorSYNOPSIS
rlecomp [ -o outfile ] Afile operator BfileDESCRIPTION
rlecomp implements an image compositor based on presence of an alpha, or matte channel the image. This extra channel usually defines a mask which represents a sort of a cookie-cutter for the image. This is the case when alpha is 255 (full coverage) for pixels inside the shape, zero outside, and between zero and 255 on the boundary. If Afile or Bfile is just a single -, then rlecomp reads that file from the standard input.The operations behave as follows (assuming the operation is "A operator B"):
- over
- The result will be the union of the two image shapes, with A obscuring B in the region of overlap.
- in
- The result is simply the image A cut by the shape of B. None of the image data of B will be in the result.
- atop
- The result is the same shape as image B, with A obscuring B where the image shapes overlap. Note this differs from over because the portion of A outside B's shape does not appear in the result.
- out
- The result image is image A with the shape of B cut out.
- xor
- The result is the image data from both images that is outside the overlap region. The overlap region will be blank.
- plus
- The result is just the sum of the image data. Output values are clipped to 255 (no overflow). This operation is actually independent of the alpha channels.
- minus
- The result of A - B, with underflow clipped to zero. The alpha channel is ignored (set to 255, full coverage).
- diff
- The result of abs(A - B). This is useful for comparing two very similar images.
- add
- The result of A + B, with overflow wrapping around (mod 256).
- subtract
- The result of A - B, with underflow wrapping around (mod 256). The add and subtract operators can be used to perform reversible transformations.
SEE ALSO
urt(1), RLE(5),"Compositing Digital Images", Porter and Duff, Proceedings of SIGGRAPH '84 p.255
AUTHORS
Rod Bogart and John W. PetersonBUGS
The other operations could be optimized as much as over is.Rlecomp assumes both input files have the same number of channels.
| December 20, 1986 | 4th Berkeley Distribution |
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