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BUILDMAP(3)		   Library Functions Manual		   BUILDMAP(3)

NAME
       buildmap	- create a color map array from	an RLE file header.

SYNOPSIS
       #include	<rle.h>

       rle_pixel ** buildmap( the_hdr, minmap, orig_gamma, new_gamma )
       rle_hdr * the_hdr;
       int minmap;
       double orig_gamma, new_gamma;

DESCRIPTION
       The color map in	the rle_hdr(3) structure is not	in the most easily
       used form.  The function	buildmap returns a pointer to a	colormap array
       with certain minimum dimensions,	making it a little easier to implement
       color mapping in	a program.  The	color map from first argument,
       the_hdr,	is used	to build the result.  If no map	is present in the_hdr,
       then an identity	map of the minimum size	will be	returned.

       The returned color map will have	at least minmap	rows or	channels, each
       of which	is at least 256	entries	long (so that indexing into the	color
       map with	an 8 bit rle_pixel value will always succeed.)

       The color map from the_hdr will be composed with	a gamma	compensation
       curve to	account	for the	gamma of the display for which the input color
       map was presumably computed.  The argument orig_gamma specifies the
       gamma of	the compensation curve.	 It would typically be the gamma of
       the original display.

       If gamma	is 0, then if a	picture	comment	image_gamma=i_gamma is
       present,	gamma will be set to 1.0/i_gamma.  Otherwise, if a comment
       display_gamma=d_gamma is	present, gamma will be set to d_gamma.	The
       gamma compensation value	for pixel i is 255*(i/255)^gamma.

       If this color map will be used directly for another display, the	gamma
       of this new display should be passed in new_gamma.

       The returned value is a pointer to an array of pointers to arrays of
       rle_pixel values.  It may be doubly indexed in C	code, so that if cmap
       is the return value, the	RGB color mapping for a	pixel pixval is
       (cmap[0][pixval], cmap[1][pixval], cmap[2][pixval]).

NOTES
       Generally, unless the user explicitly specifies the image or original
       display gamma (e.g., as with the	-i or -I flags of getx11(1), you
       should pass 0 for orig_gamma.  This lets	buildmap use the value from
       the_hdr,	if it is present.

       If you are going	to use the result of buildmap to generate values to be
       dithered, new_gamma should always be 1.0, and the display gamma (-g in
       getx11) should be passed	to dithermap(3).  If you are not planning to
       dither, then pass the user supplied display gamma as new_gamma.

       The color map storage allocated by buildmap can be released by calling
       free( map[0] ).

SEE ALSO
       dithermap(3), rle_hdr(3), librle(3), RLE(5).

AUTHOR
       Spencer W. Thomas, University of	Utah

4th Berkeley Distribution	    3/6/85			   BUILDMAP(3)

NAME | SYNOPSIS | DESCRIPTION | NOTES | SEE ALSO | AUTHOR

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