Problem caused by the change from libjpeg to libjpeg-turbo

[Marco-LIU]

Problem caused by the change from libjpeg to libjpeg-turbo

[skvark]

Hmm, I thought that I already wrote a reply here but apparently I didn't...

Anyhow, I can confirm that there seems to be differences between these libraries. Most likely the issue is related to the optimizations which have been done in libjpeg-turbo. I have no way of knowing what might cause these differences but I presume that different decoding algorithms are used under the hood. In addition, the usage SIMD extensions might cause some inaccuracies to the results. Due to the nature of the JPEG's lossy format there's no way to "fix" this issue.

I'll be changing also macOS and Windows jpeg libs to libjpeg-turbo at some point. You can always compile OpenCV by yourself if you need extremely stable environment. I hope you understand that I cannot guarantee that these builds remain consistent across releases.

Edit: See also this comment in the official repository: opencv/opencv#10887 (comment)