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Improve Dither code readability

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This commit is contained in:
Rackoon 2025-12-12 14:44:47 +01:00
parent 6d4f2b509e
commit 9efd8a1aa5
1 changed files with 29 additions and 48 deletions
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77
src/libImaging/Convert.c
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@ -1246,19 +1246,18 @@ topalette(
/* Map each pixel to the nearest palette entry */
ImagingSectionEnter(&cookie);
for (y = 0; y < imIn->ysize; y++) {
int r, r0, r1, r2;
int g, g0, g1, g2;
int b, b0, b1, b2;
int r, r0, r1;
int g, g0, g1;
int b, b0, b1;
UINT8 *in = (UINT8 *)imIn->image[y];
UINT8 *out = alpha ? (UINT8 *)imOut->image32[y] : imOut->image8[y];
int *e = errors;
r = r0 = r1 = 0;
g = g0 = g1 = 0;
b = b0 = b1 = b2 = 0;
b = b0 = b1 = 0;
for (x = 0; x < imIn->xsize; x++, in += 4) {
int d2;
INT16 *cache;
r = CLIP8(in[0] + (r + e[3 + 0]) / 16);
@ -1281,31 +1280,21 @@ topalette(
g -= (int)palette->palette[cache[0] * 4 + 1];
b -= (int)palette->palette[cache[0] * 4 + 2];
/* propagate errors (don't ask ;-) */
r2 = r;
d2 = r + r;
r += d2;
e[0] = r + r0;
r += d2;
r0 = r + r1;
r1 = r2;
r += d2;
g2 = g;
d2 = g + g;
g += d2;
e[1] = g + g0;
g += d2;
g0 = g + g1;
g1 = g2;
g += d2;
b2 = b;
d2 = b + b;
b += d2;
e[2] = b + b0;
b += d2;
b0 = b + b1;
b1 = b2;
b += d2;
/* propagate errors */
e[0] = 3*r + r0;
r0 = 5*r + r1;
r1 = r;
r = 7*r;
e[1] = 3*g + g0;
g0 = 5*g + g1;
g1 = g;
g = 7*g;
e[2] = 3*b + b0;
b0 = 5*b + b1;
b1 = b;
b = 7*b;
e += 3;
}
@ -1385,7 +1374,7 @@ tobilevel(Imaging imOut, Imaging imIn) {
/* map each pixel to black or white, using error diffusion */
ImagingSectionEnter(&cookie);
for (y = 0; y < imIn->ysize; y++) {
int l, l0, l1, l2, d2;
int l, l0, l1;
UINT8 *in = (UINT8 *)imIn->image[y];
UINT8 *out = imOut->image8[y];
@ -1398,14 +1387,10 @@ tobilevel(Imaging imOut, Imaging imIn) {
/* propagate errors */
l -= (int)out[x];
l2 = l;
d2 = l + l;
l += d2;
errors[x] = l + l0;
l += d2;
l0 = l + l1;
l1 = l2;
l += d2;
errors[x] = 3*l + l0;
l0 = 5*l + l1;
l1 = l;
l = 7*l;
}
errors[x] = l0;
@ -1416,7 +1401,7 @@ tobilevel(Imaging imOut, Imaging imIn) {
/* map each pixel to black or white, using error diffusion */
ImagingSectionEnter(&cookie);
for (y = 0; y < imIn->ysize; y++) {
int l, l0, l1, l2, d2;
int l, l0, l1;
UINT8 *in = (UINT8 *)imIn->image[y];
UINT8 *out = imOut->image8[y];
@ -1429,14 +1414,10 @@ tobilevel(Imaging imOut, Imaging imIn) {
/* propagate errors */
l -= (int)out[x];
l2 = l;
d2 = l + l;
l += d2;
errors[x] = l + l0;
l += d2;
l0 = l + l1;
l1 = l2;
l += d2;
errors[x] = 3*l + l0;
l0 = 5*l + l1;
l1 = l;
l = 7*l;
}
errors[x] = l0;