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simplify rgb to hsv conversion

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By inlining some values, the starting hue calculation can be reduced from using three subtractions and two divisions to using one subtraction and one division.
"fmod(n+1,1)" can be replaced with "n - floor(n)" due to the second parameter being 1.
The saturation calculation can be done without floating point values.
The "CLIP8"s are unnecessary because the values are already in the correct range.
This commit is contained in:
Yay295 2024-09-30 19:58:03 -05:00 committed by Yay295
parent dc3751599f
commit 6b8a97ab16
1 changed files with 35 additions and 28 deletions
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63
src/libImaging/Convert.c
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@ -310,40 +310,46 @@ rgb2bgr24(UINT8 *out, const UINT8 *in, int xsize) {
}
static void
rgb2hsv_row(UINT8 *out, const UINT8 *in) { // following colorsys.py
float h, s, rc, gc, bc, cr;
UINT8 maxc, minc;
UINT8 r, g, b;
UINT8 uh, us, uv;
rgb2hsv_row(UINT8 *out, const UINT8 *in) {
// based on Python's colorsys module
const UINT8 r = in[0];
const UINT8 g = in[1];
const UINT8 b = in[2];
const UINT8 maxc = MAX(r, MAX(g, b));
const UINT8 minc = MIN(r, MIN(g, b));
UINT8 uh, us;
const UINT8 uv = maxc;
r = in[0];
g = in[1];
b = in[2];
maxc = MAX(r, MAX(g, b));
minc = MIN(r, MIN(g, b));
uv = maxc;
if (minc == maxc) {
uh = 0;
us = 0;
} else {
cr = (float)(maxc - minc);
s = cr / (float)maxc;
rc = ((float)(maxc - r)) / cr;
gc = ((float)(maxc - g)) / cr;
bc = ((float)(maxc - b)) / cr;
if (r == maxc) {
h = bc - gc;
} else if (g == maxc) {
h = 2.0 + rc - bc;
} else {
h = 4.0 + gc - rc;
}
// incorrect hue happens if h/6 is negative.
h = fmod((h / 6.0 + 1.0), 1.0);
const UINT8 color_range = maxc - minc;
double h;
uh = (UINT8)CLIP8((int)(h * 255.0));
us = (UINT8)CLIP8((int)(s * 255.0));
const double cr = (double)color_range;
if (r == maxc) {
h = (g - b) / cr;
} else if (g == maxc) {
h = 2.0 + (b - r) / cr;
} else {
h = 4.0 + (r - g) / cr;
}
// the modulus operator in Python does not exactly match
// the modulus operator or the fmod function in C
// https://stackoverflow.com/a/3883019/3878168
// "h = (h/6.0) % 1.0" in Python can be computed as:
h = h / 6.0;
h = h - floor(h);
uh = (UINT8)(255.0 * h);
us = 255 * color_range / maxc;
}
out[0] = uh;
out[1] = us;
out[2] = uv;
@ -359,7 +365,8 @@ rgb2hsv(UINT8 *out, const UINT8 *in, int xsize) {
}
static void
hsv2rgb(UINT8 *out, const UINT8 *in, int xsize) { // following colorsys.py
hsv2rgb(UINT8 *out, const UINT8 *in, int xsize) {
// based on Python's colorsys module
int p, q, t;
UINT8 up, uq, ut;