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Merge pull request #2709 from uploadcare/alpha-composite-box

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Alpha composite fixes
This commit is contained in:
wiredfool 2017-09-19 11:13:19 +01:00 committed by GitHub
commit e5513804a3
2 changed files with 14 additions and 20 deletions
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6
PIL/Image.py
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@ -1414,9 +1414,9 @@ class Image(object):
Performance Note: Not currently implemented in-place in the core layer. Performance Note: Not currently implemented in-place in the core layer.
""" """
if not isinstance(source, tuple): if not isinstance(source, (list, tuple)):
raise ValueError("Source must be a tuple") raise ValueError("Source must be a tuple")
if not isinstance(dest, tuple): if not isinstance(dest, (list, tuple)):
raise ValueError("Destination must be a tuple") raise ValueError("Destination must be a tuple")
if not len(source) in (2, 4): if not len(source) in (2, 4):
raise ValueError("Source must be a 2 or 4-tuple") raise ValueError("Source must be a 2 or 4-tuple")
@ -1440,7 +1440,7 @@ class Image(object):
box = dest + (dest[0] + overlay.width, dest[1] + overlay.height) box = dest + (dest[0] + overlay.width, dest[1] + overlay.height)
# destination image. don't copy if we're using the whole image. # destination image. don't copy if we're using the whole image.
if dest == (0,0) + self.size: if box == (0,0) + self.size:
background = self background = self
else: else:
background = self.crop(box) background = self.crop(box)

28
libImaging/AlphaComposite.c
View File

@ -11,6 +11,7 @@
#include "Imaging.h" #include "Imaging.h"
#define PRECISION_BITS 7
typedef struct typedef struct
{ {
@ -49,13 +50,11 @@ ImagingAlphaComposite(Imaging imDst, Imaging imSrc)
ImagingCopyInfo(imOut, imDst); ImagingCopyInfo(imOut, imDst);
for (y = 0; y < imDst->ysize; y++) { for (y = 0; y < imDst->ysize; y++) {
rgba8* dst = (rgba8*) imDst->image[y]; rgba8* dst = (rgba8*) imDst->image[y];
rgba8* src = (rgba8*) imSrc->image[y]; rgba8* src = (rgba8*) imSrc->image[y];
rgba8* out = (rgba8*) imOut->image[y]; rgba8* out = (rgba8*) imOut->image[y];
for (x = 0; x < imDst->xsize; x ++) { for (x = 0; x < imDst->xsize; x ++) {
if (src->a == 0) { if (src->a == 0) {
// Copy 4 bytes at once. // Copy 4 bytes at once.
*out = *dst; *out = *dst;
@ -64,25 +63,20 @@ ImagingAlphaComposite(Imaging imDst, Imaging imSrc)
// Each variable has extra meaningful bits. // Each variable has extra meaningful bits.
// Divisions are rounded. // Divisions are rounded.
// This code uses trick from Paste.c:
// (a + (2 << (n-1)) - 1) / ((2 << n)-1)
// almost equivalent to:
// tmp = a + (2 << (n-1)), ((tmp >> n) + tmp) >> n
UINT32 tmpr, tmpg, tmpb; UINT32 tmpr, tmpg, tmpb;
UINT16 blend = dst->a * (255 - src->a); UINT32 blend = dst->a * (255 - src->a);
UINT16 outa255 = src->a * 255 + blend; UINT32 outa255 = src->a * 255 + blend;
// There we use 7 bits for precision. // There we use 7 bits for precision.
// We could use more, but we go beyond 32 bits. // We could use more, but we go beyond 32 bits.
UINT16 coef1 = src->a * 255 * 255 * 128 / outa255; UINT32 coef1 = src->a * 255 * 255 * (1<<PRECISION_BITS) / outa255;
UINT16 coef2 = 255 * 128 - coef1; UINT32 coef2 = 255 * (1<<PRECISION_BITS) - coef1;
tmpr = src->r * coef1 + dst->r * coef2 + (0x80 << 7); tmpr = src->r * coef1 + dst->r * coef2;
out->r = SHIFTFORDIV255(tmpr) >> 7; tmpg = src->g * coef1 + dst->g * coef2;
tmpg = src->g * coef1 + dst->g * coef2 + (0x80 << 7); tmpb = src->b * coef1 + dst->b * coef2;
out->g = SHIFTFORDIV255(tmpg) >> 7; out->r = SHIFTFORDIV255(tmpr + (0x80<<PRECISION_BITS)) >> PRECISION_BITS;
tmpb = src->b * coef1 + dst->b * coef2 + (0x80 << 7); out->g = SHIFTFORDIV255(tmpg + (0x80<<PRECISION_BITS)) >> PRECISION_BITS;
out->b = SHIFTFORDIV255(tmpb) >> 7; out->b = SHIFTFORDIV255(tmpb + (0x80<<PRECISION_BITS)) >> PRECISION_BITS;
out->a = SHIFTFORDIV255(outa255 + 0x80); out->a = SHIFTFORDIV255(outa255 + 0x80);
} }