A small test example showing ghostscript recompresses some pngs into jpegs rendering pdfScale.sh's output lossy.

The issue is disscussed here here.

Dependencies:

• img2pdf
• python + pymupdf
• pdfScale.sh (ghostscript)
• imagemagick
• pdfimages

Starting with in.png:

We santifize with imagemagick into sample.png:

We convert to pdf with img2pdf, dump using pdfimages and compare with magick:

Result: img2pdf is lossless.

Same with pdfScale.sh:

Result: GhostScript (via pdfScale.sh) recompresses to jpeg and introduces artifacts.

Now just GhostScript:

Result: GhostScript (alone) introduces artifacts.

Finally, pdfScale.py:

Result: pdfScale.py is lossless.

Conclusion: GhostScript is lossy and pdfScale.sh is affected.