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Merge pull request #26215 from meeseeksmachine/auto-backport-of-pr-25824-on-v3.7.x
Backport PR #25824 on branch v3.7.x (pdf: Use explicit palette when saving indexed images)
2 parents 8d42212 + 399ebe1 commit 349849b

21 files changed

+46
-22
lines changed

‎lib/matplotlib/backends/backend_pdf.py

Lines changed: 21 additions & 17 deletions
Original file line numberDiff line numberDiff line change
@@ -1757,39 +1757,43 @@ def _writeImg(self, data, id, smask=None):
17571757
'Subtype': Name('Image'),
17581758
'Width': width,
17591759
'Height': height,
1760-
'ColorSpace': Name({1: 'DeviceGray',
1761-
3: 'DeviceRGB'}[color_channels]),
1760+
'ColorSpace': Name({1: 'DeviceGray', 3: 'DeviceRGB'}[color_channels]),
17621761
'BitsPerComponent': 8}
17631762
if smask:
17641763
obj['SMask'] = smask
17651764
if mpl.rcParams['pdf.compression']:
17661765
if data.shape[-1] == 1:
17671766
data = data.squeeze(axis=-1)
1767+
png = {'Predictor': 10, 'Colors': color_channels, 'Columns': width}
17681768
img = Image.fromarray(data)
17691769
img_colors = img.getcolors(maxcolors=256)
17701770
if color_channels == 3 and img_colors is not None:
1771-
# Convert to indexed color if there are 256 colors or fewer
1772-
# This can significantly reduce the file size
1771+
# Convert to indexed color if there are 256 colors or fewer. This can
1772+
# significantly reduce the file size.
17731773
num_colors = len(img_colors)
1774-
# These constants were converted to IntEnums and deprecated in
1775-
# Pillow 9.2
1776-
dither = getattr(Image, 'Dither', Image).NONE
1777-
pmode = getattr(Image, 'Palette', Image).ADAPTIVE
1778-
img = img.convert(
1779-
mode='P', dither=dither, palette=pmode, colors=num_colors
1780-
)
1774+
palette = np.array([comp for _, color in img_colors for comp in color],
1775+
dtype=np.uint8)
1776+
palette24 = ((palette[0::3].astype(np.uint32) << 16) |
1777+
(palette[1::3].astype(np.uint32) << 8) |
1778+
palette[2::3])
1779+
rgb24 = ((data[:, :, 0].astype(np.uint32) << 16) |
1780+
(data[:, :, 1].astype(np.uint32) << 8) |
1781+
data[:, :, 2])
1782+
indices = np.argsort(palette24).astype(np.uint8)
1783+
rgb8 = indices[np.searchsorted(palette24, rgb24, sorter=indices)]
1784+
img = Image.fromarray(rgb8, mode='P')
1785+
img.putpalette(palette)
17811786
png_data, bit_depth, palette = self._writePng(img)
17821787
if bit_depth is None or palette is None:
17831788
raise RuntimeError("invalid PNG header")
1784-
palette = palette[:num_colors * 3] # Trim padding
1785-
obj['ColorSpace'] = Verbatim(
1786-
b'[/Indexed /DeviceRGB %d %s]'
1787-
% (num_colors - 1, pdfRepr(palette)))
1789+
palette = palette[:num_colors * 3] # Trim padding; remove for Pillow>=9
1790+
obj['ColorSpace'] = [Name('Indexed'), Name('DeviceRGB'),
1791+
num_colors - 1, palette]
17881792
obj['BitsPerComponent'] = bit_depth
1789-
color_channels = 1
1793+
png['Colors'] = 1
1794+
png['BitsPerComponent'] = bit_depth
17901795
else:
17911796
png_data, _, _ = self._writePng(img)
1792-
png = {'Predictor': 10, 'Colors': color_channels, 'Columns': width}
17931797
else:
17941798
png = None
17951799
self.beginStream(

‎lib/matplotlib/tests/baseline_images/test_agg_filter/agg_filter_alpha.pdf

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‎lib/matplotlib/tests/baseline_images/test_axes/imshow.pdf

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‎lib/matplotlib/tests/baseline_images/test_axes/imshow_clip.pdf

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‎lib/matplotlib/tests/baseline_images/test_backend_pdf/grayscale_alpha.pdf

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‎lib/matplotlib/tests/baseline_images/test_image/bbox_image_inverted.pdf

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‎lib/matplotlib/tests/baseline_images/test_image/figimage.pdf

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‎lib/matplotlib/tests/baseline_images/test_image/image_alpha.pdf

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‎lib/matplotlib/tests/baseline_images/test_image/image_interps.pdf

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‎lib/matplotlib/tests/baseline_images/test_image/image_placement.pdf

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‎lib/matplotlib/tests/baseline_images/test_image/image_shift.pdf

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‎lib/matplotlib/tests/baseline_images/test_image/imshow.pdf

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‎lib/matplotlib/tests/baseline_images/test_image/imshow_masked_interpolation.pdf

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‎lib/matplotlib/tests/baseline_images/test_image/log_scale_image.pdf

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‎lib/matplotlib/tests/baseline_images/test_image/no_interpolation_origin.pdf

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‎lib/matplotlib/tests/baseline_images/test_image/rotate_image.pdf

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‎lib/matplotlib/tests/baseline_images/test_patheffects/patheffect1.pdf

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‎lib/matplotlib/tests/baseline_images/test_streamplot/streamplot_colormap.pdf

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‎lib/matplotlib/tests/baseline_images/test_tightlayout/tight_layout5.pdf

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‎lib/matplotlib/tests/test_backend_pdf.py

Lines changed: 24 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -131,6 +131,30 @@ def test_composite_image():
131131
assert len(pdf._file._images) == 2
132132

133133

134+
def test_indexed_image():
135+
# An image with low color count should compress to a palette-indexed format.
136+
pikepdf = pytest.importorskip('pikepdf')
137+
138+
data = np.zeros((256, 1, 3), dtype=np.uint8)
139+
data[:, 0, 0] = np.arange(256) # Maximum unique colours for an indexed image.
140+
141+
rcParams['pdf.compression'] = True
142+
fig = plt.figure()
143+
fig.figimage(data, resize=True)
144+
buf = io.BytesIO()
145+
fig.savefig(buf, format='pdf', dpi='figure')
146+
147+
with pikepdf.Pdf.open(buf) as pdf:
148+
page, = pdf.pages
149+
image, = page.images.values()
150+
pdf_image = pikepdf.PdfImage(image)
151+
assert pdf_image.indexed
152+
pil_image = pdf_image.as_pil_image()
153+
rgb = np.asarray(pil_image.convert('RGB'))
154+
155+
np.testing.assert_array_equal(data, rgb)
156+
157+
134158
def test_savefig_metadata(monkeypatch):
135159
pikepdf = pytest.importorskip('pikepdf')
136160
monkeypatch.setenv('SOURCE_DATE_EPOCH', '0')

‎lib/matplotlib/tests/test_image.py

Lines changed: 1 addition & 5 deletions
Original file line numberDiff line numberDiff line change
@@ -753,11 +753,7 @@ def test_log_scale_image():
753753
ax.set(yscale='log')
754754

755755

756-
# Increased tolerance is needed for PDF test to avoid failure. After the PDF
757-
# backend was modified to use indexed color, there are ten pixels that differ
758-
# due to how the subpixel calculation is done when converting the PDF files to
759-
# PNG images.
760-
@image_comparison(['rotate_image'], remove_text=True, tol=0.35)
756+
@image_comparison(['rotate_image'], remove_text=True)
761757
def test_rotate_image():
762758
delta = 0.25
763759
x = y = np.arange(-3.0, 3.0, delta)

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