mlib_ImageColorDitherInit(3MLIB)			    mediaLib Library Functions				  mlib_ImageColorDitherInit(3MLIB)

NAME

       mlib_ImageColorDitherInit - initialization for image dithering

SYNOPSIS

       cc [ flag... ] file... -lmlib [ library... ]
       #include <mlib.h>

       mlib_status mlib_ImageColorDitherInit(void **colormap, const mlib_s32 *dimensions,
	    mlib_type intype, mlib_type outtype, mlib_s32 channels, mlib_s32 entries,
	    mlib_s32 offset, void **lut);

DESCRIPTION

       The  mlib_ImageColorDitherInit() function creates an internal data structure, colormap, which can be used by one of the following functions
       for image dithering:

	 mlib_ImageColorErrorDiffusion3x3
	 mlib_ImageColorErrorDiffusionMxN
	 mlib_ImageColorOrderedDither8x8
	 mlib_ImageColorOrderedDitherMxN

       The lut might have either 1 or 3 channels. The type of the lut can be one of the following:

	 MLIB_BYTE in, MLIB_BYTE out (i.e., BYTE-to-BYTE)
	 MLIB_BIT in, MLIB_BYTE out (i.e., BIT-to-BYTE)

       If dimensions == NULL, then no colorcube will be created. In this case, the user-provided lookup table, lut, will be used for dithering.

       If dimensions != NULL, then a colorcube is created from scratch in a way shown in the following example.

       To dither an RGB image of type MLIB_BYTE to a color-indexed image of type MLIB_BYTE, we can use the following parameters:

	 mlib_s32  dimensions[] = {2, 3, 4};
	 mlib_type intype = MLIB_BYTE;
	 mlib_type outtype = MLIB_BYTE;
	 mlib_s32  channels = 3;
	 mlib_s32  offset = 6;

       These values would lead to the creation of a colorcube that would dither red values in the source image to one of 2 red levels, green  val-
       ues to one of 3 green levels, and blue values to one of 4 blue levels.  You could picture this colorcube as a cube with dimensions of 2, 3,
       and 4.  The index values assigned to the elements in that cube can be described by the following lookup table:

		      | 	       |		|
	  Indexes     |   Red Values   | Green Values	| Blue Values
       ---------------+----------------+----------------+---------------
       0	      | 	       |		|
       ---------------+----------------+----------------+---------------
       ...	      | 	       |		|
       ---------------+----------------+----------------+---------------
       5	      | 	       |		|
       ---------------+----------------+----------------+---------------

       6	      | 0	       | 0		|0
       ---------------+----------------+----------------+---------------
       7	      | 255	       | 0		|0
       ---------------+----------------+----------------+---------------
       8	      | 0	       | 128		|0
       ---------------+----------------+----------------+---------------
       9	      | 255	       | 128		|0
       ---------------+----------------+----------------+---------------
       10	      | 0	       | 255		|0
       ---------------+----------------+----------------+---------------
       11	      | 255	       | 255		|0
       ---------------+----------------+----------------+---------------
       12	      | 0	       | 0		|85
       ---------------+----------------+----------------+---------------
       13	      | 255	       | 0		|85
       ---------------+----------------+----------------+---------------
       14	      | 0	       | 128		|85
       ---------------+----------------+----------------+---------------
       15	      | 255	       | 128		|85
       ---------------+----------------+----------------+---------------
       16	      | 0	       | 255		|85
       ---------------+----------------+----------------+---------------
       17	      | 255	       | 255		|85
       ---------------+----------------+----------------+---------------
       18	      | 0	       | 0		|170
       ---------------+----------------+----------------+---------------
       19	      | 255	       | 0		|170
       ---------------+----------------+----------------+---------------
       20	      | 0	       | 128		|170
       ---------------+----------------+----------------+---------------
       21	      | 255	       | 128		|170
       ---------------+----------------+----------------+---------------
       22	      | 0	       | 255		|170
       ---------------+----------------+----------------+---------------
       23	      | 255	       | 255		|170
       ---------------+----------------+----------------+---------------
       24	      | 0	       | 0		|255
       ---------------+----------------+----------------+---------------
       25	      | 255	       | 0		|255
       ---------------+----------------+----------------+---------------
       26	      | 0	       | 128		|255
       ---------------+----------------+----------------+---------------
       27	      | 255	       | 128		|255
       ---------------+----------------+----------------+---------------
       28	      | 0	       | 255		|255
       ---------------+----------------+----------------+---------------
       29	      | 255	       | 255		|255
       ---------------+----------------+----------------+---------------
       ...	      | 	       |		|

       The distance between level changes in each channel of the lookup table is determined by the following formulas:

	 multipliers[0] = signof(dimensions[0])*1;
	 multipliers[i] = signof(dimensions[i])*
			  abs(multipliers[i-1]*dimension[i-1]);

       A negative dimensions[i], so as to a negative multipliers[i], indicates that the values in a color ramp for  channel  i	should	appear	in
       decreasing as opposed to increasing order.

       For each channel i, the values of the levels are determined by the following formulas:

	 double delta = (dataMax - dataMin)/(abs(dimensions[i]) - 1);
	 int levels[j] = (int)(j*delta + 0.5);

       where dataMax and dataMin are the maximum and minimum values, respectively, for data type intype.

       Whenever  a  colorcube  is created, if lut != NULL, the lookup table will be filled according to the colorcube and supplied parameters like
       offset.	For the example shown above, the lookup table will start from line 6.  In this case, it is the user's responsibility  to  allocate
       memory for the lookup table.

PARAMETERS

       The function takes the following arguments:

       colormap      Internal data structure for image dithering.

       dimensions     Dimensions of the colorcube in the colormap structure.

       intype	     Data type of the source image and the lookup table.

       outtype	     Data type of the destination indexed image.

       channels      Number of channels of the lookup table and source image.

       entries	     Number of entries of the lookup table.

       offset	     Index offset of the lookup table.

       lut	     Lookup table.

RETURN VALUES

       The function returns MLIB_SUCCESS if successful. Otherwise it returns MLIB_FAILURE.

ATTRIBUTES

       See attributes(5) for descriptions of the following attributes:

       +-----------------------------+-----------------------------+
       |      ATTRIBUTE TYPE	     |	    ATTRIBUTE VALUE	   |
       +-----------------------------+-----------------------------+
       |Interface Stability	     |Committed 		   |
       +-----------------------------+-----------------------------+
       |MT-Level		     |MT-Safe			   |
       +-----------------------------+-----------------------------+

SEE ALSO

       mlib_ImageColorDitherFree(3MLIB), mlib_ImageColorErrorDiffusion3x3(3MLIB), mlib_ImageColorErrorDiffusionMxN(3MLIB), mlib_ImageColorOrdered-
       Dither8x8(3MLIB), mlib_ImageColorOrderedDitherMxN(3MLIB), attributes(5)

SunOS 5.11							    2 Mar 2007					  mlib_ImageColorDitherInit(3MLIB)