RLEQUANT(1)RLEQUANT(1)NAMErlequant - variance based color quantization for RLE images
SYNOPSISrlequant [ -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 inter‐
nal 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 digi‐
tized. 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 other‐
wise 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.
-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 - map‐
size. 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 speci‐
fied, 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.
EXAMPLESrlequant 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 (differ‐
ent) 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 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 dither‐
ing.
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 intermedi‐
ate storage.
SEE ALSOmcut(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.
4th Berkeley Distribution June 12, 1990 RLEQUANT(1)
