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Merge pull request #4144 from jansol/master

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Stop decoding BC1 punchthrough alpha in BC2&3
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Andrew Murray 2021-04-15 20:24:52 +10:00 committed by GitHub
commit 1e074f5040
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3 changed files with 23 additions and 5 deletions
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Tests/images/dxt5-colorblock-alpha-issue-4142.dds Normal file
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15
Tests/test_file_dds.py
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@ -195,6 +195,21 @@ def test_short_file():
short_file()
def test_dxt5_colorblock_alpha_issue_4142():
""" Check that colorblocks are decoded correctly in DXT5"""
with Image.open("Tests/images/dxt5-colorblock-alpha-issue-4142.dds") as im:
px = im.getpixel((0, 0))
assert px[0] != 0
assert px[1] != 0
assert px[2] != 0
px = im.getpixel((1, 0))
assert px[0] != 0
assert px[1] != 0
assert px[2] != 0
def test_unimplemented_pixel_format():
with pytest.raises(NotImplementedError):
with Image.open("Tests/images/unimplemented_pixel_format.dds"):

13
src/libImaging/BcnDecode.c
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@ -69,7 +69,7 @@ decode_565(UINT16 x) {
}
static void
decode_bc1_color(rgba *dst, const UINT8 *src) {
decode_bc1_color(rgba *dst, const UINT8 *src, int separate_alpha) {
bc1_color col;
rgba p[4];
int n, cw;
@ -84,7 +84,10 @@ decode_bc1_color(rgba *dst, const UINT8 *src) {
r1 = p[1].r;
g1 = p[1].g;
b1 = p[1].b;
if (col.c0 > col.c1) {
/* NOTE: BC2 and BC3 reuse BC1 color blocks but always act like c0 > c1 */
if (col.c0 > col.c1 || separate_alpha) {
p[2].r = (2 * r0 + 1 * r1) / 3;
p[2].g = (2 * g0 + 1 * g1) / 3;
p[2].b = (2 * b0 + 1 * b1) / 3;
@ -150,13 +153,13 @@ decode_bc3_alpha(char *dst, const UINT8 *src, int stride, int o) {
static void
decode_bc1_block(rgba *col, const UINT8 *src) {
decode_bc1_color(col, src);
decode_bc1_color(col, src, 0);
}
static void
decode_bc2_block(rgba *col, const UINT8 *src) {
int n, bitI, byI, av;
decode_bc1_color(col, src + 8);
decode_bc1_color(col, src + 8, 1);
for (n = 0; n < 16; n++) {
bitI = n * 4;
byI = bitI >> 3;
@ -168,7 +171,7 @@ decode_bc2_block(rgba *col, const UINT8 *src) {
static void
decode_bc3_block(rgba *col, const UINT8 *src) {
decode_bc1_color(col, src + 8);
decode_bc1_color(col, src + 8, 1);
decode_bc3_alpha((char *)col, src, sizeof(col[0]), 3);
}