0.68: Discontinuities when downscaling large images

Reported bugs that have been closed and/or resolved

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0.68: Discontinuities when downscaling large images

Post by Anamon » Thu Oct 02, 2014 7:35 pm

Last year there were reports about horizontal or vertical black lines when downscaling large images. This bug has been fixed, but in v0.68 I seem to have a similar, maybe related issue.

I've only noticed horizontal lines so far. The lines I'm noticing are not black or any other single colour, they just manifest themselves in discontinuities in the picture. It's as if one row of pixels in the downscaled image was missing, and the row above and below it are next to each other.
As this does not introduce "foreign" colours into the display, it can be hard to see. But I assume that every downscaled picture contains one or more of them somewhere. It's just that depending on the content of the picture, they range from usually almost completely invisible, up to for some images extremely disruptive.

I have high-quality zoom-in and zoom-out enabled in options. It seems as this might be a bug in the filters used for downscaling. I don't have the same problem when using classic XnView.
I have snapped a few examples here while going through a few photos, and tried to indicate where you can see the lines without obfuscating them. Let me know if any of you can reproduce/determine this on your own systems.
I'm running XnViewMP 0.68 from May 15 2014 on Windows 7 x64 with a GeForce GTX 570 and driver v344.11 (in case anything is done with hardware acceleration here...)

Example 1
Example 2
Example 3
Example 4
Example 5 (Just found this one, this is one of the extreme examples I was on about!)

Edit: I find the lines particularly noticeable when flicking through a number of images of the same resolution. Then, the lines always seem to appear at the same positions, and they pop out because their location is fixed while the pictures underneath change. That's when they usually feel the most disturbing to me.

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Re: Discontinuities when downscaling large images

Post by smithson » Fri Dec 26, 2014 2:52 pm

I can confirm, I notice this all the time. Here is an example with diagonal stripes. Resizing produces discontinuities in a grid pattern

https://www.googledrive.com/host/0Bwfb9 ... 495372.gif
https://www.googledrive.com/host/0Bwfb9 ... 504475.png
https://www.googledrive.com/host/0Bwfb9 ... 512906.png

edit: I also have a nvidia card

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Re: Discontinuities when downscaling large images

Post by helmut » Mon Dec 05, 2016 8:38 pm

This problem is supposed to be fixed in XnView MP 0.84 beta 1. Could you please try and confirm the bug fix?

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Re: 0.68: Discontinuities when downscaling large images

Post by deus-ex » Tue Feb 05, 2019 10:53 am

Hi Pierre,

I'm downscaling images on a regular basis and I haven't noticed any of the reported issues with all recent releases of XnViewMP. I just ran some additional tests with v0.93 64-bit on Windows 10, using several images with varying content, trying all available downscaling filters. I confirm that downscaling works as intended without producing any unwanted artifacts in the image.
Best regards,

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