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media/thumbnailer: Better quality for 1-bit / 8-bit color palette images (#2142)
Pillow will use nearest neighbour as the resampling algorithm if the source image is either 1-bit or a color palette using 8 bits. If we convert to RGB before scaling, we'll probably get a better result.
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changelog.d/2142.feature
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changelog.d/2142.feature
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Improve quality of thumbnails for 1-bit/8-bit color palette images.
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@ -82,13 +82,21 @@ class Thumbnailer(object):
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else:
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else:
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return (max_height * self.width) // self.height, max_height
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return (max_height * self.width) // self.height, max_height
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def _resize(self, width, height):
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# 1-bit or 8-bit color palette images need converting to RGB
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# otherwise they will be scaled using nearest neighbour which
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# looks awful
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if self.image.mode in ["1", "P"]:
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self.image = self.image.convert("RGB")
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return self.image.resize((width, height), Image.ANTIALIAS)
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def scale(self, width, height, output_type):
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def scale(self, width, height, output_type):
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"""Rescales the image to the given dimensions.
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"""Rescales the image to the given dimensions.
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Returns:
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Returns:
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BytesIO: the bytes of the encoded image ready to be written to disk
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BytesIO: the bytes of the encoded image ready to be written to disk
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"""
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"""
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scaled = self.image.resize((width, height), Image.ANTIALIAS)
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scaled = self._resize(width, height)
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return self._encode_image(scaled, output_type)
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return self._encode_image(scaled, output_type)
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def crop(self, width, height, output_type):
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def crop(self, width, height, output_type):
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@ -107,13 +115,13 @@ class Thumbnailer(object):
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"""
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"""
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if width * self.height > height * self.width:
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if width * self.height > height * self.width:
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scaled_height = (width * self.height) // self.width
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scaled_height = (width * self.height) // self.width
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scaled_image = self.image.resize((width, scaled_height), Image.ANTIALIAS)
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scaled_image = self._resize(width, scaled_height)
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crop_top = (scaled_height - height) // 2
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crop_top = (scaled_height - height) // 2
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crop_bottom = height + crop_top
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crop_bottom = height + crop_top
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cropped = scaled_image.crop((0, crop_top, width, crop_bottom))
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cropped = scaled_image.crop((0, crop_top, width, crop_bottom))
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else:
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else:
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scaled_width = (height * self.width) // self.height
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scaled_width = (height * self.width) // self.height
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scaled_image = self.image.resize((scaled_width, height), Image.ANTIALIAS)
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scaled_image = self._resize(scaled_width, height)
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crop_left = (scaled_width - width) // 2
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crop_left = (scaled_width - width) // 2
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crop_right = width + crop_left
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crop_right = width + crop_left
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cropped = scaled_image.crop((crop_left, 0, crop_right, height))
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cropped = scaled_image.crop((crop_left, 0, crop_right, height))
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