mlib_ImageColorDitherInit(mediaLib Library Funmlib_ImageColorDitherInit(3MLIB)NAMEmlib_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 func‐
tions 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
values to one of 3 green levels, and blue values to one of 4 blue lev‐
els. 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 decreas‐
ing as opposed to increasing order.
For each channel i, the values of the levels are determined by the fol‐
lowing 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, respec‐
tively, 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 off‐
set. For the example shown above, the lookup table will start from
line 6. In this case, it is the user's responsibility to allocate mem‐
ory 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 ALSOmlib_ImageColorDitherFree(3MLIB), mlib_ImageColorErrorDiffu‐
sion3x3(3MLIB), mlib_ImageColorErrorDiffusionMxN(3MLIB), mlib_ImageCol‐
orOrderedDither8x8(3MLIB), mlib_ImageColorOrderedDitherMxN(3MLIB),
attributes(5)SunOS 5.10 2 Mar 2007 mlib_ImageColorDitherInit(3MLIB)
