Is JPEG lossless when the quality is set to 100?

Question

I understand that JPEG is a lossy compression standard and that a quality factor determines the degree of compression and therefore the amount of data loss.

But when the quality number is set to 100, is the resulting jpeg lossless?

Answer 1

Jpeg is a loss, regardless of configuration. At 100, you just get the maximum loss.

This is easy enough to verify. Pick up a simple .bmp, compress it to q = 100 jpeg, and then re-extract it into .bmp. Use Gimp / Photoshop to make the “difference” between the two bitmaps, and you will see a loss - it will be much less noticeable than when converting q = 50 or q = 1, but still be present.

Answer 2

There is a lossless JPEG format , but it is not widely supported, and you do not get it by adjusting the quality setting - this is a completely different process.

Answer 3

According to wikipedia , No.

jpeg 100 has a compression ratio of 2.6: 1. The compression method is usually lost, which means that some original image information is lost and cannot be restored, which can affect image quality.

There is an additional lossless mode defined in the JPEG standard; however, this mode is not widely supported in products.