Manual Reference Pages - RLECOMP (1)
rlecomp - Digital image compositor
Afile operator Bfile
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"):
The result will be the union of the two
image shapes, with A obscuring B in the region of overlap.
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.
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 Bs shape does not appear
in the result.
The result image is image A with the shape of B cut out.
The result is the image data from both images that is
outside the overlap region. The overlap region will be blank.
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.
The result of A - B, with underflow clipped to zero. The
alpha channel is ignored (set to 255, full coverage).
The result of abs(A - B).
This is useful for comparing two very similar images.
The result of A + B, with overflow wrapping
around (mod 256).
The result of A - B, with underflow wrapping around
(mod 256). The add and subtract operators can be
used to perform reversible transformations.
"Compositing Digital Images", Porter and Duff,
Proceedings of SIGGRAPH 84 p.255
Rod Bogart and John W. Peterson
The other operations could be optimized as much as
Rlecomp assumes both input files have the same number of channels.
|1 ||RLECOMP (1) ||December 20, 1986 |
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