Pixmap created from CMYK JPEG delivers RGB format

[JorjMcKie]

Discussed in #3057

^{Originally posted by dothinking January 18, 2024}
With upgrading PyMuPDF from 1.23.8 to 1.23.15, fitz.Pixmap() doesn't work as expected. Do I miss something, or if it's an upstream issue.

sample.pdf

PyMuPdf 1.23.8

>>> import fitz
>>> fitz.version
('1.23.8', '1.23.7', '20231219000001')
>>> doc = fitz.Document('sample.pdf')
>>> doc[0].get_images(full=True)
[(17, 0, 1731, 1331, 8, 'DeviceCMYK', '', 'Im0', 'DCTDecode', 0)]
>>> pix = fitz.Pixmap(doc, 17)
>>> pix.colorspace
Colorspace(CS_CMYK) - DeviceCMYK
>>> pix = fitz.Pixmap(fitz.csRGB, pix)
>>> pix.save('sample-1.png')                      <- perfect

PyMuPdf 1.23.15

>>> import fitz
>>> fitz.version
('1.23.15', '1.23.9', '20240116000001')
>>> doc = fitz.Document('sample.pdf')
>>> doc[0].get_images(full=True)
[(17, 0, 1731, 1331, 8, 'DeviceCMYK', '', 'Im0', 'DCTDecode', 0)]    <- color space = DeviceCMYK
>>> pix = fitz.Pixmap(doc, 17)
>>> pix.colorspace
Colorspace(CS_RGB) - DeviceRGB                     <- color space seems changed to DeviceRGB
>>> pix = fitz.Pixmap(fitz.csRGB, pix)
>>> pix.save('sample-2.png')                   <- the png color is different from the source
```</div>

[julian-smith-artifex-com]

Thanks for the report and for including the reproducer.

I have a fix in review, and will hopefully make a new release with the fix later today.

[julian-smith-artifex-com]

Fixed in 1.23.16.