Bilevel scans, CCITT fax images and 2- or 4-bit gray TIFFs were rejected with
"sample buffer too short". The `tiff` crate returns such samples packed, most
significant bits first, eight, four or two to a byte with each row padded to a
whole byte; the converter expects one byte per sample. They are now spread out
one per byte and scaled to 0–255 (255, 85 and 17 times the sample: exact) before
conversion. 3-, 5-, 6- and 7-bit samples, and planar images with more than one
sample narrower than a byte, are refused with an "unsupported" error.
The new test builds 1-bit (both photometric conventions, a width that leaves row
padding, set padding bits), 2-bit and 4-bit strips in code, plus a truncated
strip that must fail cleanly; it fails without the fix with the old error. A
600×400 bilevel image, uncompressed and CCITT G4, now decodes to the same pixels
PIL reads from it.
The module documentation no longer claims palette support: the `tiff` crate
refuses RGBPalette images on every read path, so the palette branch here has
never been reached. The parity row lists palette TIFF as missing.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
A WhiteIsZero (PhotometricInterpretation 0) gray TIFF opened as a negative at
every bit depth. The `tiff` crate (0.11) already inverts those samples as it
reads them, for every layout it accepts, and refuses the WhiteIsZero layouts it
can't invert; the decoder here then inverted them a second time. WhiteIsZero is
common in scanner and fax output, and CCITT fax images use it by definition.
The second inversion is removed. The new test builds 8- and 16-bit WhiteIsZero
and BlackIsZero strips in code and fails without the fix (the lowest sample
came out black instead of white).
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
