Bug in Opening JPEG files

[victorengel]

It appears Neat Image may have a problem opening JPEG files. I've started a thread at DPREVIEW on the subject, but perhaps here is a better place. My post is located at http://forums.dpreview.com/forums/read. ... ge=7337080

In essence, there seems to be noise introduced around dark edges by Neat Images when opening JPEG files. Take an image with dark edges, open in Neat Image, take a screen capture and compare the same image opened in another application. They should match, but they don't. To really see the artifact clearly, oversharpen with a small radius and/or view a magnified image.

[NITeam]

In essence, there seems to be noise introduced around dark edges by Neat Images when opening JPEG files. Take an image with dark edges, open in Neat Image, take a screen capture and compare the same image opened in another application. They should match, but they don't.

This is not necessarily so. There may be different JPEG processing libraries used by different applications and usually they do produce different results.

We will check the effect that you refer to. Probably the issue is related to the JPEG library we use.

Thank you for reporting,
Vlad

[NITeam]

I have checked NI behaviour on it and I think I know what causes the problem.

It is not a bug.

Everything starts with the image, which in itself is encoded with the JPEG chroma subsampling of 4:2:2. Because of this, simply by decoding this image using standard JPEG procedures (say from the IJG library) you will inevitably get those horizontal blocks.

That is why many JPEG libraries additionally provide a smoothing filter that slightly blurs the chroma channels in such images during decoding. The result of this is much less visible horizontal blocks. That is what you see in the image from Paintshop Pro.

Now, Neat Image does use a different JPEG library as compared with Paintshop Pro and initially I thought that it was the difference in libraries that caused those different results.

However the real reason is NI does not use those smoothing routines, but in principle this could be done. So, the solution was obvious - I have switched the smoothing routines on and the result became practically the same as in the image from Paintshop Pro.

The original image in itself remains subsampled but now we have a way to make it look a bit better when opened in Neat Image. So, how you read a JPEG does matter. What you usually see in an image viewer or image editor is made to look better than what is really there in the file.

Thank you very much for bringing this issue to our attention. With your help the very next update of Neat Image will work better with such images.

Thanks a lot!

Vlad

[victorengel]

I've tried NI 3.17, and my problem has been completely eliminated. See my thread at http://forums.dpreview.com/forums/read. ... ge=7435374

[NITeam]

Thank you for confirming that.

Vlad