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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),
(111, 207, 206, 110),
(127, 254, 127, 0),
(255, 255, 255, 0) if mode == "RGBA" else (127, 254, 127, 0),
(207, 207, 239, 239),
(191, 191, 190, 191),
(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)
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):
im = Image.new(mode="RGB", size=(300, 100))
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;
for (x = 0; x < xsize; x++) {
for (i = 0; i < pixelsize; i++) {
*out = BLEND(*mask, *out, ink[i], tmp1);
out++;
UINT8 channel_mask = *mask;
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++;
}
}