Investigating this, the corruption depends upon the geometry of the image - it is possible to crop the image to a size that is not corrupted in the PDF.
e.g. the pnm after this cropping option is not corrupted: convert corrupt_no_compression.pnm -crop 790x400+500+900 corrupt_no_compression_cropped.pnm but cropping only the width, the corruption is still there, but less: convert corrupt_no_compression.pnm -crop 790x3506+500+0 corrupt_no_compression_cropped.pnm equally, cropping only the height, the corruption is also still there, in a similar magnitude to the original: convert corrupt_no_compression.pnm -crop 2480x400+0+900 corrupt_no_compression_cropped.pnm
signature.asc
Description: OpenPGP digital signature
