RLEQUANT(1) 1 (June 12, 1990) RLEQUANT(1)
NAME
rlequant - variance based color quantization for RLE images
SYNOPSIS
rlequant [ -b bits ] [ -c ] [ -d ] [ -f ] [ -i cubeside ] [
-m ] [ -n colors ] [ -r mapfile ] [ -o outfile ] [
infile ]
DESCRIPTION
This program quantizes the colors in an RLE image using a
variance-based method. See colorquant(3) for more details
on the method.
-b bits
The colors in the input image will be "prequantized" to
this many bits before applying the variance-based
method. Two internal tables of size 2^(3*bits) are
allocated, so values of bits greater than 6 are likely
to cause thrashing or may prevent the program from
running at all. The default value of bits is 5. It
must be less than or equal to 8 and greater than 0.
-c Only the color map will be output; the image will not
be digitized. The output file will be a 0x0 RLE file
with a color map, suitable for input to rleldmap(1),
rledither(1), or rlequant-r.
-d Floyd Steinberg dithering is performed on the output.
This is very helpful for images being quantized to a
small number of colors.
-f If this option is specified, a faster approximation
will be used. In most cases, the error so introduced
will be barely noticeable.
-i cubeside
Initializes the output color map with a "color cube" of
size cubeside^3. I.e., if -i 2 were specified, the 8
corners of the color cube (black, red, green, blue,
yellow, cyan, magenta, white) would be added to the
output colormap. This reduces the number of colors
available for quantization. The color cube will be
used to quantize the output image, but will not
otherwise affect the choice of representative colors.
-m Computes a single color map suitable for quantizing all
the input images. This is useful when the quantized
images will be used as a "movie" (e.g., with the -m
flag of getx11(1)). The input may not come from a pipe
when this option is specified, unless -c is also
specified.
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RLEQUANT(1) 1 (June 12, 1990) RLEQUANT(1)-n colors
The output image will be quantized to at most colors
colors. It might have fewer if the input image has
only a few colors itself. The default value of colors
is 256 - cubesize^3 - mapsize. It must be less than or
equal to 256. If a color cube (-c) or an input map
(-r) is given, colors may be 0; otherwise it must be
greater than 0.
-r mapfile
The color map from the RLE file mapfile will be added
to the output color map. The number of colors in the
input color map, mapsize is calculated as follows: If a
color_map_length comment is present in mapfile, its
value is used. If not, the size of the color map
(usually 256) is used (the rlehdr(1) program will
display the color map size and the comment, if
present). The input color map will be used to quantize
the output image, but will not otherwise affect the
choice of representative colors. If the combination -n
0 -r mapfile is specified, then rlequant will just
quantize (and dither, if requested) the input images to
the given colormap. This is usually faster than using
rledither.
-o outfile
The output will be written to the file outfile. If not
specified, or if outfile is "-", the output will be
written to the standard output stream.
infile
This file contains one or more concatenated RLE images.
Each will be processed in turn. A separate
quantization map will be constructed for each image.
If not specified, or if infile is "-", the image(s)
will be read from the standard input stream.
EXAMPLES
rlequant file.rle
Quantizes file.rle to 256 colors using a 5-bit pre-
quantization. If file.rle has multiple images, each
will get its own (different) colormap.
rlequant-m file.rle
Quantizes file.rle to 256 colors using a 5-bit pre-
quantization. If file.rle has multiple images, they
will all be used to choose the color map, and will all
be quantized to the same color map.
cat *.rle | rlequant-m -c >map.rle ;
cat *.rle | rlequant-n 0 -r map.rle
Computes a single colormap based on all the images in
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RLEQUANT(1) 1 (June 12, 1990) RLEQUANT(1)
the files *.rle, then quantizes each image to that
color map. The output is the stream of quantized
images.
rlequant-i 4 -d file.rle
Compute 192 representative colors for each image in
file.rle, add a 4x4x4 color cube to the resulting color
map, and then quantize the image to the resulting set
of colors with dithering.
rlequant-b 6 file.rle
Quantize file.rle to 256 colors using a 6-bit
prequantization. This provides slightly more precision
in color matching than does a 5-bit prequantization.
It also runs significantly slower and requires
approximately 8 times the memory for its intermediate
storage.
SEE ALSO
mcut(1), rledither(1), rlehdr(1), urt(1), colorquant(3),
RLE(5).
AUTHOR
Spencer W. Thomas
Craig Kolb (Yale University) wrote the color quantization
code.
Rod Bogart wrote the dithering code.
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