Save 1 mode PDF using CCITTFaxDecode filter #6470
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radarhere
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Aug 1, 2022
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https://opensource.adobe.com/dc-acrobat-sdk-docs/standards/pdfstandards/pdf/PDF32000_2008.pdf#page=38 indicates that K should be <0 for Group 4 encoding
On the next page of that document, it describes BlackIs1, that allows the colors to be inverted.
This was referenced Aug 1, 2022
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radarhere
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Aug 1, 2022
src/PIL/PdfImagePlugin.py
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| ImageFile._save(im, op, [("hex", (0, 0) + im.size, 0, im.mode)]) | ||
| elif filter == "CCITTFaxDecode": | ||
| original_strip_size = TiffImagePlugin.STRIP_SIZE | ||
| TiffImagePlugin.STRIP_SIZE = math.ceil(im.width / 8) * im.height |
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In writing this PR, I found that it was necessary to save the image as a single strip. This has actually been pointed out before, in #5740
radarhere
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Aug 1, 2022
| # aim for given strip size (64 KB by default) when using libtiff writer | ||
| if libtiff: | ||
| rows_per_strip = 1 if stride == 0 else min(STRIP_SIZE // stride, im.size[1]) | ||
| im_strip_size = encoderinfo.get("strip_size", STRIP_SIZE) |
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Rather than updating STRIP_SIZE and needing to reset it afterwards, I've added "strip_size" as a TIFF encoder argument.
This was referenced Aug 22, 2022
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Resolves #6453
The issue requests the CCITTTaxDecode filter be using to save 1 mode PDFs, to reduce file size.