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Manual Reference Pages  -  TO8 (1)


to8 - Convert a 24 bit RLE file to eight bits using dithering.


See Also


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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