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#include <stdlib.h>
#include "gif.h"
#define distance_squared(a, b) \
(((a)[2] - (b)[0]) * ((a)[2] - (b)[0]) + ((a)[1] - (b)[1]) * ((a)[1] - (b)[1]) + \
((a)[0] - (b)[2]) * ((a)[0] - (b)[2]))
static int compare_color_component(const void *left, const void *right)
{
int l = ((const unsigned char *)left)[0];
int r = ((const unsigned char *)right)[0];
return l - r;
}
void median_cut(unsigned char *pixels, unsigned char *color_table, int num_pixels, int num_colors, int num_channels)
{
/* Perform a color quantization similar to the modified median cut quantization algorithm */
if (num_pixels <= 0)
{
int i;
for (i = 0; i < num_colors; i++)
{
color_table[4 * i + 0] = 0;
color_table[4 * i + 1] = 0;
color_table[4 * i + 2] = 0;
color_table[4 * i + 3] = 0;
}
return;
}
if (num_colors == 1)
{
color_table[0] = pixels[num_pixels / 2 * num_channels + 2]; /* B */
color_table[1] = pixels[num_pixels / 2 * num_channels + 1]; /* G */
color_table[2] = pixels[num_pixels / 2 * num_channels + 0]; /* R */
color_table[3] = pixels[num_pixels / 2 * num_channels + 3]; /* A */
}
else
{
int i;
int cut_axis;
unsigned char cut_value;
int left_pixels;
unsigned char minred, mingreen, minblue, maxred, maxgreen, maxblue;
minred = maxred = pixels[0];
mingreen = maxgreen = pixels[1];
minblue = maxblue = pixels[2];
for (i = 1; i < num_pixels; i++)
{
if (pixels[i * num_channels + 0] < minred) minred = pixels[i * num_channels + 0];
if (pixels[i * num_channels + 0] > maxred) maxred = pixels[i * num_channels + 0];
if (pixels[i * num_channels + 1] < mingreen) mingreen = pixels[i * num_channels + 1];
if (pixels[i * num_channels + 1] > maxgreen) maxgreen = pixels[i * num_channels + 1];
if (pixels[i * num_channels + 2] < minblue) minblue = pixels[i * num_channels + 2];
if (pixels[i * num_channels + 2] > maxblue) maxblue = pixels[i * num_channels + 2];
}
if (maxred - minred < maxgreen - mingreen)
{
if (maxgreen - mingreen < maxblue - minblue)
{
cut_axis = 2;
cut_value = (minblue + maxblue) / 2;
}
else
{
cut_axis = 1;
cut_value = (mingreen + maxgreen) / 2;
}
}
else
{
if (maxred - minred < maxblue - minblue)
{
cut_axis = 2;
cut_value = (minblue + maxblue) / 2;
}
else
{
cut_axis = 0;
cut_value = (minred + maxred) / 2;
}
}
qsort(pixels + cut_axis, num_pixels, num_channels, compare_color_component);
for (left_pixels = num_colors / 2;
(left_pixels < num_pixels - num_colors / 2) && pixels[left_pixels * num_channels + cut_axis] < cut_value;
left_pixels++)
;
median_cut(pixels, color_table, left_pixels, num_colors / 2, num_channels);
median_cut(pixels + left_pixels * num_channels, color_table + num_colors / 2 * num_channels,
num_pixels - left_pixels, num_colors / 2, num_channels);
}
}
unsigned char color_index_for_rgb(const unsigned char *rgb_pixel, const unsigned char *color_table,
int color_table_size, int num_channels)
{
/* Return the color index most closely matching this RGB color. */
int color_index;
int closest_color_index = 0;
float closest_color_index_distance = -1;
for (color_index = 0; color_index < color_table_size; ++color_index)
{
float color_index_distance = distance_squared(&color_table[color_index * num_channels], rgb_pixel);
if (closest_color_index_distance < 0 || closest_color_index_distance > color_index_distance)
{
closest_color_index_distance = color_index_distance;
closest_color_index = color_index;
}
}
return closest_color_index;
}
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