以下是基于
CompuPhase-颜色度量的“低成本逼近”的颜色差,但避免了平方根函数(因此测量了颜色差的平方,这对比较目的来说是可以接受的),并将结果缩放以避免由整数除法引起的精度损失。它将颜色元组数组按“最红”到“最不红”的顺序排序。
比较使中灰比黑色更红,黑色比白色更红,这似乎相当武断!
#include <stdio.h>
#include <stdlib.h>
struct rgb {
unsigned char r;
unsigned char g;
unsigned char b;
};
long color_dist_squared(const struct rgb *c1, const struct rgb *c2)
{
long rsum = c1->r + c2->r;
long dr = (long)c1->r - (long)c2->r;
long dg = (long)c1->g - (long)c2->g;
long db = (long)c1->b - (long)c2->b;
return (((1024 + rsum) * dr * dr) + (2048 * dg * dg) +
((1534 - rsum) * db * db));
}
long antiredness_squared(const struct rgb *c)
{
const struct rgb pure_red = { .r = 255, .g = 0, .b = 0 };
return color_dist_squared(&pure_red, c);
}
int compar_antiredness(const void *a, const void *b)
{
const struct rgb *ca = (const struct rgb *)a;
const struct rgb *cb = (const struct rgb *)b;
long ara = antiredness_squared(ca);
long arb = antiredness_squared(cb);
long diff = ara - arb;
return (diff > 0) - (diff < 0);
}
int main(void)
{
struct rgb colors[] = {
{ .r = 125, .g = 0, .b = 0 },
{ .r = 150, .g = 255, .b = 0 },
{ .r = 100, .g = 20, .b = 21 },
{ .r = 255, .g = 21, .b = 22 },
{ .r = 0, .g = 0, .b = 0 },
{ .r = 255, .g = 255, .b = 255 },
{ .r = 128, .g = 128, .b = 128 },
{ .r = 255, .g = 0, .b = 0 },
};
size_t num_colors = sizeof(colors) / sizeof(colors[0]);
size_t i;
printf("Unsorted colors:\n");
for (i = 0; i < num_colors; i++) {
printf("[%zu] R=%u, G=%u, B=%u\n", i, (unsigned)colors[i].r,
(unsigned)colors[i].g, (unsigned)colors[i].b);
}
printf("\n");
qsort(colors, num_colors, sizeof(colors[0]), compar_antiredness);
printf("Colors sorted from most red to least red:\n");
for (i = 0; i < num_colors; i++) {
printf("[%zu] R=%u, G=%u, B=%u\n", i, (unsigned)colors[i].r,
(unsigned)colors[i].g, (unsigned)colors[i].b);
}
return 0;
}
以上的输出:
Unsorted colors:
[0] R=125, G=0, B=0
[1] R=150, G=255, B=0
[2] R=100, G=20, B=21
[3] R=255, G=21, B=22
[4] R=0, G=0, B=0
[5] R=255, G=255, B=255
[6] R=128, G=128, B=128
[7] R=255, G=0, B=0
Colors sorted from most red to least red:
[0] R=255, G=0, B=0
[1] R=255, G=21, B=22
[2] R=125, G=0, B=0
[3] R=100, G=20, B=21
[4] R=128, G=128, B=128
[5] R=0, G=0, B=0
[6] R=150, G=255, B=0
[7] R=255, G=255, B=255
编辑:当然,使用以下函数从最绿到最不绿或从最蓝到最不蓝排序同样容易:
long antigreenness_squared(const struct rgb *c)
{
const struct rgb pure_green = { .r = 0, .g = 255, .b = 0 };
return color_dist_squared(&pure_green, c);
}
int compar_antigreenness(const void *a, const void *b)
{
const struct rgb *ca = (const struct rgb *)a;
const struct rgb *cb = (const struct rgb *)b;
long aga = antigreenness_squared(ca);
long agb = antigreenness_squared(cb);
long diff = aga - agb;
return (diff > 0) - (diff < 0);
}
long antiblueness_squared(const struct rgb *c)
{
const struct rgb pure_blue = { .r = 0, .g = 0, .b = 255 };
return color_dist_squared(&pure_blue, c);
}
int compar_antiblueness(const void *a, const void *b)
{
const struct rgb *ca = (const struct rgb *)a;
const struct rgb *cb = (const struct rgb *)b;
long aba = antiblueness_squared(ca);
long abb = antiblueness_squared(cb);
long diff = aba - abb;
return (diff > 0) - (diff < 0);
}
stored_*
变量的值。 - Chris Turner