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Speed up Image.getchannel(), Image.merge(), Image.putalpha() and Image.split() #9675

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Merged
hugovk merged 1 commit into from
Jul 1, 2026
+69 −51
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Speed up Image.getchannel(), Image.merge(), Image.putalpha() and Image.split() #9675

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120 changes: 69 additions & 51 deletions src/libImaging/Bands.c
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Original file line number Diff line number Diff line change
Expand Up @@ -47,16 +47,19 @@ ImagingGetBand(Imaging imIn, int band) {
}

/* Extract band from image */

@radarhere radarhere Jun 16, 2026

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Suggested change
/* Extract band from image */
// Extract band from image

Maybe this is nicer than having a multiline comment next to a single line comment?

@akx akx Jun 16, 2026

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Not sure it matters that much? I just didn't want to touch the original code or comment format here :)

for (y = 0; y < imIn->ysize; y++) {
UINT8 *in = (UINT8 *)imIn->image[y] + band;
UINT8 *out = imOut->image8[y];
// restrict safe: imIn is read-only, imOut is a fresh allocation.
int xsize = imIn->xsize;
int ysize = imIn->ysize;
for (y = 0; y < ysize; y++) {
UINT8 *restrict in = (UINT8 *)imIn->image[y] + band;
UINT8 *restrict out = imOut->image8[y];
x = 0;
for (; x < imIn->xsize - 3; x += 4) {
for (; x < xsize - 3; x += 4) {
UINT32 v = MAKE_UINT32(in[0], in[4], in[8], in[12]);
memcpy(out + x, &v, sizeof(v));
in += 16;
}
for (; x < imIn->xsize; x++) {
for (; x < xsize; x++) {
out[x] = *in;
in += 4;
}
Expand Down Expand Up @@ -92,33 +95,37 @@ ImagingSplit(Imaging imIn, Imaging bands[4]) {
}

/* Extract bands from image */

@radarhere radarhere Jun 16, 2026

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Suggested change
/* Extract bands from image */
// Extract bands from image

// restrict safe: imIn is read-only and each band is a distinct fresh
// allocation, so none of in/out0..out3 alias each other.
int xsize = imIn->xsize;
int ysize = imIn->ysize;
if (imIn->bands == 2) {
for (y = 0; y < imIn->ysize; y++) {
UINT8 *in = (UINT8 *)imIn->image[y];
UINT8 *out0 = bands[0]->image8[y];
UINT8 *out1 = bands[1]->image8[y];
for (y = 0; y < ysize; y++) {
UINT8 *restrict in = (UINT8 *)imIn->image[y];
UINT8 *restrict out0 = bands[0]->image8[y];
UINT8 *restrict out1 = bands[1]->image8[y];
x = 0;
for (; x < imIn->xsize - 3; x += 4) {
for (; x < xsize - 3; x += 4) {
UINT32 v = MAKE_UINT32(in[0], in[4], in[8], in[12]);
memcpy(out0 + x, &v, sizeof(v));
v = MAKE_UINT32(in[0 + 3], in[4 + 3], in[8 + 3], in[12 + 3]);
memcpy(out1 + x, &v, sizeof(v));
in += 16;
}
for (; x < imIn->xsize; x++) {
for (; x < xsize; x++) {
out0[x] = in[0];
out1[x] = in[3];
in += 4;
}
}
} else if (imIn->bands == 3) {
for (y = 0; y < imIn->ysize; y++) {
UINT8 *in = (UINT8 *)imIn->image[y];
UINT8 *out0 = bands[0]->image8[y];
UINT8 *out1 = bands[1]->image8[y];
UINT8 *out2 = bands[2]->image8[y];
for (y = 0; y < ysize; y++) {
UINT8 *restrict in = (UINT8 *)imIn->image[y];
UINT8 *restrict out0 = bands[0]->image8[y];
UINT8 *restrict out1 = bands[1]->image8[y];
UINT8 *restrict out2 = bands[2]->image8[y];
x = 0;
for (; x < imIn->xsize - 3; x += 4) {
for (; x < xsize - 3; x += 4) {
UINT32 v = MAKE_UINT32(in[0], in[4], in[8], in[12]);
memcpy(out0 + x, &v, sizeof(v));
v = MAKE_UINT32(in[0 + 1], in[4 + 1], in[8 + 1], in[12 + 1]);
Expand All @@ -127,22 +134,22 @@ ImagingSplit(Imaging imIn, Imaging bands[4]) {
memcpy(out2 + x, &v, sizeof(v));
in += 16;
}
for (; x < imIn->xsize; x++) {
for (; x < xsize; x++) {
out0[x] = in[0];
out1[x] = in[1];
out2[x] = in[2];
in += 4;
}
}
} else {
for (y = 0; y < imIn->ysize; y++) {
UINT8 *in = (UINT8 *)imIn->image[y];
UINT8 *out0 = bands[0]->image8[y];
UINT8 *out1 = bands[1]->image8[y];
UINT8 *out2 = bands[2]->image8[y];
UINT8 *out3 = bands[3]->image8[y];
for (y = 0; y < ysize; y++) {
UINT8 *restrict in = (UINT8 *)imIn->image[y];
UINT8 *restrict out0 = bands[0]->image8[y];
UINT8 *restrict out1 = bands[1]->image8[y];
UINT8 *restrict out2 = bands[2]->image8[y];
UINT8 *restrict out3 = bands[3]->image8[y];
x = 0;
for (; x < imIn->xsize - 3; x += 4) {
for (; x < xsize - 3; x += 4) {
UINT32 v = MAKE_UINT32(in[0], in[4], in[8], in[12]);
memcpy(out0 + x, &v, sizeof(v));
v = MAKE_UINT32(in[0 + 1], in[4 + 1], in[8 + 1], in[12 + 1]);
Expand All @@ -153,7 +160,7 @@ ImagingSplit(Imaging imIn, Imaging bands[4]) {
memcpy(out3 + x, &v, sizeof(v));
in += 16;
}
for (; x < imIn->xsize; x++) {
for (; x < xsize; x++) {
out0[x] = in[0];
out1[x] = in[1];
out2[x] = in[2];
Expand Down Expand Up @@ -195,10 +202,15 @@ ImagingPutBand(Imaging imOut, Imaging imIn, int band) {
}

/* Insert band into image */

@radarhere radarhere Jun 16, 2026

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Suggested change
/* Insert band into image */
// Insert band into image

for (y = 0; y < imIn->ysize; y++) {
UINT8 *in = imIn->image8[y];
UINT8 *out = (UINT8 *)imOut->image[y] + band;
for (x = 0; x < imIn->xsize; x++) {
// restrict safe: imIn is single-band (bands verified 1),
// imOut must be multi-band or we would have shortcut out above,
// so they're distinct images with disparate buffers.
int xsize = imIn->xsize;
int ysize = imIn->ysize;
for (y = 0; y < ysize; y++) {
UINT8 *restrict in = imIn->image8[y];
UINT8 *restrict out = (UINT8 *)imOut->image[y] + band;
for (x = 0; x < xsize; x++) {
*out = in[x];
out += 4;
}
Expand Down Expand Up @@ -228,9 +240,11 @@ ImagingFillBand(Imaging imOut, int band, int color) {
color = CLIP8(color);

/* Insert color into image */
for (y = 0; y < imOut->ysize; y++) {
UINT8 *out = (UINT8 *)imOut->image[y] + band;
for (x = 0; x < imOut->xsize; x++) {
int xsize = imOut->xsize;
int ysize = imOut->ysize;
for (y = 0; y < ysize; y++) {
UINT8 *restrict out = (UINT8 *)imOut->image[y] + band;
for (x = 0; x < xsize; x++) {
*out = (UINT8)color;
out += 4;
}
Expand Down Expand Up @@ -279,33 +293,37 @@ ImagingMerge(const ModeID mode, Imaging bands[4]) {
return ImagingCopy2(imOut, firstBand);
}

// restrict safe: the input bands are read-only and imOut is a fresh
// allocation, so none of in0..in3/out alias each other.
int xsize = imOut->xsize;
int ysize = imOut->ysize;
if (imOut->bands == 2) {
for (y = 0; y < imOut->ysize; y++) {
UINT8 *in0 = bands[0]->image8[y];
UINT8 *in1 = bands[1]->image8[y];
UINT32 *out = (UINT32 *)imOut->image32[y];
for (x = 0; x < imOut->xsize; x++) {
for (y = 0; y < ysize; y++) {
UINT8 *restrict in0 = bands[0]->image8[y];
UINT8 *restrict in1 = bands[1]->image8[y];
UINT32 *restrict out = (UINT32 *)imOut->image32[y];
for (x = 0; x < xsize; x++) {
out[x] = MAKE_UINT32(in0[x], 0, 0, in1[x]);
}
}
} else if (imOut->bands == 3) {
for (y = 0; y < imOut->ysize; y++) {
UINT8 *in0 = bands[0]->image8[y];
UINT8 *in1 = bands[1]->image8[y];
UINT8 *in2 = bands[2]->image8[y];
UINT32 *out = (UINT32 *)imOut->image32[y];
for (x = 0; x < imOut->xsize; x++) {
for (y = 0; y < ysize; y++) {
UINT8 *restrict in0 = bands[0]->image8[y];
UINT8 *restrict in1 = bands[1]->image8[y];
UINT8 *restrict in2 = bands[2]->image8[y];
UINT32 *restrict out = (UINT32 *)imOut->image32[y];
for (x = 0; x < xsize; x++) {
out[x] = MAKE_UINT32(in0[x], in1[x], in2[x], 0);
}
}
} else if (imOut->bands == 4) {
for (y = 0; y < imOut->ysize; y++) {
UINT8 *in0 = bands[0]->image8[y];
UINT8 *in1 = bands[1]->image8[y];
UINT8 *in2 = bands[2]->image8[y];
UINT8 *in3 = bands[3]->image8[y];
UINT32 *out = (UINT32 *)imOut->image32[y];
for (x = 0; x < imOut->xsize; x++) {
for (y = 0; y < ysize; y++) {
UINT8 *restrict in0 = bands[0]->image8[y];
UINT8 *restrict in1 = bands[1]->image8[y];
UINT8 *restrict in2 = bands[2]->image8[y];
UINT8 *restrict in3 = bands[3]->image8[y];
UINT32 *restrict out = (UINT32 *)imOut->image32[y];
for (x = 0; x < xsize; x++) {
out[x] = MAKE_UINT32(in0[x], in1[x], in2[x], in3[x]);
}
}
Expand Down
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