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Special-case opaque pixels in RGBa unpacker

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Avoid the expensive multiply and divide when the pixel is opaque.
On my system, this change gives a 5.76x speedup loading an opaque image
with this call:

    PIL.Image.frombuffer('RGBA', (1000, 1000), buf, 'raw', 'RGBa', 0, 1)
This commit is contained in:
Benjamin Gilbert 2015-01-24 01:13:58 -05:00
parent adad71c759
commit 77b020b374
1 changed files with 6 additions and 1 deletions
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7
libImaging/Unpack.c
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@ -638,7 +638,12 @@ unpackRGBa(UINT8* out, const UINT8* in, int pixels)
int a = in[3];
if (!a)
out[R] = out[G] = out[B] = out[A] = 0;
else {
else if (a == 255) {
out[R] = in[0];
out[G] = in[1];
out[B] = in[2];
out[A] = a;
} else {
out[R] = CLIP(in[0] * 255 / a);
out[G] = CLIP(in[1] * 255 / a);
out[B] = CLIP(in[2] * 255 / a);