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to8 - Convert a 24 bit RLE file to eight bits using dithering.
to8
[ -g display_gamma ] [ -{iI} image_gamma ] [ -o outfile ] [ infile ]
To8
Converts an image with 24 bit pixel values (eight bits each of red, green
and blue) to eight bits of color using a dithered color map (the special
color map is automatically written into the output file). If no input file
is specified, to8 reads from stdin. If no output file is specified with
-o it writes the result to the standard output.
Other options allow control
over the gamma, or contrast, of the image. The dithering process assumes
that the incoming image has a gamma of 1.0 (i.e., a 200 in the input represents
an intensity twice that of a 100.) If this is not the case, the input values
must be adjusted before dithering via the -i or -I option. The input file
may also specify the gamma of the image via a picture comment (see below).
The output display is assumed to have a gamma of 2.5 (standard for color
TV monitors). This may be modified via the -g option if a display with a
different gamma is used.
To8 will put a picture comment into the output
file indicating the display gamma assumed in constructing the dithering
color map.
- -i image_gamma
- Specify the gamma (contrast) of the image.
A low contrast image, suited for direct display without compensation on
a high contrast monitor (as most monitors are) will have a gamma of less
than one. The default image gamma is 1.0. Image gamma may also be specified
by a picture comment in the RLE (5)
file of the form image_gamma=gamma.
The command line argument will override the value in the file if specified.
- -I image_gamma
- An alternate method of specifying the image gamma, the number
following -I is the gamma of the display for which the image was originally
computed (and is therefore 1.0 divided by the actual gamma of the image).
Image display gamma may also be specified by a picture comment in the
RLE (5)
file of the form display_gamma=gamma. The command line argument
will override the value in the file if specified.
- -g display_gamma
- Specify
the gamma of the X display monitor. The default value is 2.5, suitable
for most color TV monitors (this is the gamma value assumed by the NTSC
video standard).
- -o outfile
- If specified, the output will be written to this
file. If outfile is "-", or if it is not specified, the output will be
written to the standard output stream.
tobw(1)
, getx11(1)
, mcut(1)
,
rlequant(1)
, urt(1)
, dither(3)
, RLE(5)
.
Spencer Thomas
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