TO8(1) 1 (Month DD, YYYY) TO8(1)
NAME
to8 - Convert a 24 bit RLE file to eight bits using
dithering.
SYNOPSIS
to8 [ -g display_gamma ] [ -{iI} image_gamma ] [ -o outfile
] [ infile ]
DESCRIPTION
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.
OPTIONS
-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
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TO8(1) 1 (Month DD, YYYY) TO8(1)
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.
SEE ALSO
tobw(1), getx11(1), mcut(1), rlequant(1), urt(1), dither(3),
RLE(5).
AUTHOR
Spencer Thomas
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