Can't produce a Quality 0 JPEG

[Queuecumber]

What did you do?

im.save(output_path / i.with_suffix('.jpg').name, quality=0)

What did you expect to happen?

A JPEG with libjpeg quantization equivalent to zero quality to be output.

What actually happened?

A JPEG with libjpeg quantization equivalent to quality 75 was output

What are your OS, Python and Pillow versions?

• OS: Linux
• Python: 3.5
• Pillow:

Comments

I do research in image compression and as part of that research I wanted to produce some quality 0 JPEG files, the quantization matrix for that should filled with 255, dumping the resulting JPEGs quantization tables with djpeg I see that they are quality 75, and from the source code it looks like quality=0 indicates to use the defaulty quality which is 75.

Quality zero is a completely valid quality for libjpeg, but it doesn't work in Pillow. I'm not sure how many people care about quality 0 JPEGs so it might not be worth fixing but I still figured I'd leave this here.

[radarhere]

I've created PR #4440 to resolve this.