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Consider transparency when drawing text on an RGBA image

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This commit is contained in:
Andrew Murray 2020-04-19 20:56:17 +10:00
parent a0d8e550ec
commit e10cab42f1
4 changed files with 19 additions and 3 deletions
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Tests/images/transparent_background_text.png Normal file
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Width:  |  Height:  |  Size: 1.2 KiB

2
Tests/test_image_paste.py
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@ -236,7 +236,7 @@ class TestImagingPaste:
[ [
(127, 191, 254, 191), (127, 191, 254, 191),
(111, 207, 206, 110), (111, 207, 206, 110),
(127, 254, 127, 0), (255, 255, 255, 0) if mode == "RGBA" else (127, 254, 127, 0),
(207, 207, 239, 239), (207, 207, 239, 239),
(191, 191, 190, 191), (191, 191, 190, 191),
(207, 206, 111, 112), (207, 206, 111, 112),

12
Tests/test_imagefont.py
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@ -150,6 +150,18 @@ class TestImageFont:
assert_image_equal(img_path, img_filelike) assert_image_equal(img_path, img_filelike)
def test_transparent_background(self):
im = Image.new(mode="RGBA", size=(300, 100))
draw = ImageDraw.Draw(im)
ttf = self.get_font()
txt = "Hello World!"
draw.text((10, 10), txt, font=ttf)
target = "Tests/images/transparent_background_text.png"
with Image.open(target) as target_img:
assert_image_similar(im, target_img, 4.09)
def test_textsize_equal(self): def test_textsize_equal(self):
im = Image.new(mode="RGB", size=(300, 100)) im = Image.new(mode="RGB", size=(300, 100))
draw = ImageDraw.Draw(im) draw = ImageDraw.Draw(im)

8
src/libImaging/Paste.c
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@ -379,9 +379,13 @@ fill_mask_L(Imaging imOut, const UINT8* ink, Imaging imMask,
UINT8* mask = (UINT8*) imMask->image[y+sy]+sx; UINT8* mask = (UINT8*) imMask->image[y+sy]+sx;
for (x = 0; x < xsize; x++) { for (x = 0; x < xsize; x++) {
for (i = 0; i < pixelsize; i++) { for (i = 0; i < pixelsize; i++) {
*out = BLEND(*mask, *out, ink[i], tmp1); UINT8 channel_mask = *mask;
out++; if (strcmp(imOut->mode, "RGBA") == 0 && i != 3) {
channel_mask = 255 - (255 - channel_mask) * (1 - (255 - out[3]) / 255);
}
out[i] = BLEND(channel_mask, out[i], ink[i], tmp1);
} }
out += pixelsize;
mask++; mask++;
} }
} }