[Gimp-user] Gimp 2.8 pixelation on resize
ofnuts wrote: I do agree that this specific implementation/version of the algorithm on this specific part of this specific photo looks better. Period(*) Ok, but my problem is that I have mostly blackheaded sheeps in my cattle. And renat's case show's that this is not only a matter of scanning printed docs. Maybe I had post it in dev list? Wbr, Gunnar -- wk_ (via www.gimpusers.com/forums) ___ gimp-user-list mailing list List address:gimp-user-list@gnome.org List membership: https://mail.gnome.org/mailman/listinfo/gimp-user-list List archives: https://mail.gnome.org/archives/gimp-user-list
[Gimp-user] Gimp 2.8 pixelation on resize
ofnuts wrote: And renat's case show's that this is not only a matter of scanning printed docs. Moreover, I faced the similar grid while downscaling many other landscape pics with huge flat - but not absolutely flat - surfaces, be it sky hit by noise a bit, or a sea-view with a small waves. So this problem may be pretty common. -- renat (via www.gimpusers.com/forums) ___ gimp-user-list mailing list List address:gimp-user-list@gnome.org List membership: https://mail.gnome.org/mailman/listinfo/gimp-user-list List archives: https://mail.gnome.org/archives/gimp-user-list
Re: [Gimp-user] Gimp 2.8 pixelation on resize
On Wed, 2015-04-22 at 21:11 +0200, wk_ wrote: Liam wrote: If it is a scan of a printed document is is to be expected that there may be moiré patterns, even if the scanner is set to apply a descreen filter. I feel that there is something lost from my original post. Like it never reached to the list. I see still it in archive, I point it for reference: http://www.mail-archive.com/gimp-user-list%40gnome.org/msg08063.html Have you looked my original scan I linked there? Yes, I looked at it in detail. Yes, it is scan of printed document. But this is not problem. I have more than 20 years experience of scanning printed docs. Please remember that we don't know your background. Problem is, when I use same settings in Gimp 2.6 and 2.8 for scaling down the same sample I got completely different results. This is probably because the default downscaling method changed. The new method is better for some things and worse for others. And unfortunately, 2.8 is so much worse. So we must use additional processing before scaling. I like to have full workflow foolproof and simple, so I can delegate it whomever I need. Adding additional levels of processing is bad practice in my environment. You can change the default downscaling method. I tried with two different computers (both Gimp 2.8) and got same ugly result. It seemed unbelievable, that new version may have such comedown and no one has noticed such behaviour, so I asked here for others experience. If that's the case, the grid is liable to appear at any time on scaling down the image, or possibly with other image editing operations, both in gimp and in other programs, especially with 8- bit per channel colour. It's a function of the image, not of the software. So, if I take same image and scale it down with 3 different tools (Gimp 2.8, Gimp 2.6 and ImageMagick), I got 3 different results and it is function of image??? How? It is a combination of the image and the tools, of course. I deal with these often in processing scans. You can use a frequency decomposition to remove them, or you can do a guassian blur as I think others have suggested, before scaling down. I do, if needed. In 2.6 it was not necessary, generally. In 2.8 it is not avoidable, that's my problem. It depends on the interpolation method that's used - in a recent gimp 2.9 snapshot I found the pattern appeard with one interpolation method but not another. The default interpolation method I think changes from time to time in different GIMP releases. I explicitly used Sinc interpolation in both cases, with 2.6 and with 2.8. Well, you didn't say that before. However, I do believe the code changed. I think in 2.6 the dialogue was misleading as Cubic was used for downscaling in that case. Wbr, Gunnar ___ gimp-user-list mailing list List address:gimp-user-list@gnome.org List membership: https://mail.gnome.org/mailman/listinfo/gimp-user-list List archives: https://mail.gnome.org/archives/gimp-user-list
[Gimp-user] Gimp 2.8 pixelation on resize
So, if you scale down to 51% (which is about 2x) you first do a 2px Gaussian blur. Result here: http://imgur.com/iZB3lmw Do you agree that Gimp 2.6 version looks still out much better? http://pasteboard.co/27ib9Dvx.png Wbr, Gunnar -- wk_ (via www.gimpusers.com/forums) ___ gimp-user-list mailing list List address:gimp-user-list@gnome.org List membership: https://mail.gnome.org/mailman/listinfo/gimp-user-list List archives: https://mail.gnome.org/archives/gimp-user-list
Re: [Gimp-user] Gimp 2.8 pixelation on resize
See https://en.wikipedia.org/wiki/Aliasing So, if you scale down to 51% (which is about 2x) you first do a 2px Gaussian blur. Result here: http://imgur.com/iZB3lmw On 20/04/15 09:25, wk_ wrote: Steve wrote: I got the original image you posted, and enhanced the contrast with duplicate layers set to Overlay mode, plus some color curve tweaking: This is not my original post you are talking about, it is already renat's posting to this topic. So for interest of clarity i post my OP again, because there are described simple steps I did: Hi! After installing new Gimp 2.8 (on Lubuntu 14.04 64bit) for our employee, she noticed, that scanned images are going pixelated (like moire effect) much more than with previous Gimp when scaling images down. I made a little set to comparision. This is clip of original scanned (300dpi) image: http://pbrd.co/1CTKhHB This is how it looks after scaling down (Sinc algorythm) to the 51 percent http://pbrd.co/1CTKHO7 Same procedure with Gimp 2.6: http://pbrd.co/1CTL9vR And scaled down with ImageMagick: (convert -geometry 292x360 100precent.png 51percent_imagemagick.png) http://pbrd.co/1CTLgYg I like most the Gimp 2.6 version, it has no pixelation, but black characters have still sharp edges. ImageMagick is also not bad. But Gimp 2.8 version is not for my . What is wrong here? Is there something to make it better? TIA, Gunnar ___ gimp-user-list mailing list List address:gimp-user-list@gnome.org List membership: https://mail.gnome.org/mailman/listinfo/gimp-user-list List archives: https://mail.gnome.org/archives/gimp-user-list
Re: [Gimp-user] Gimp 2.8 pixelation on resize
On Sun, 2015-04-19 at 22:20 +0200, wk_ wrote: Steve wrote: I have never seen anything exactly like this, so I am confident that it is not an artifact introduced by scaling an image in the GIMP. I don't understand your way to this conclusion. In my original post I have source scan, If it is a scan of a printed document is is to be expected that there may be moiré patterns, even if the scanner is set to apply a descreen filter. If that's the case, the grid is liable to appear at any time on scaling down the image, or possibly with other image editing operations, both in gimp and in other programs, especially with 8-bit per channel colour. It's a function of the image, not of the software. I deal with these often in processing scans. You can use a frequency decomposition to remove them, or you can do a guassian blur as I think others have suggested, before scaling down. which I scaled down with 3 different tools (Gimp 2.8, Gimp 2.6 and ImageMаgick). With first one Moire pattern appears, but not with others. How it could be not realated to Gimp 2.8? The process is easily reproducible. It depends on the interpolation method that's used - in a recent gimp 2.9 snapshot I found the pattern appeard with one interpolation method but not another. The default interpolation method I think changes from time to time in different GIMP releases. Liam Wbr, Gunnar ___ gimp-user-list mailing list List address:gimp-user-list@gnome.org List membership: https://mail.gnome.org/mailman/listinfo/gimp-user-list List archives: https://mail.gnome.org/archives/gimp-user-list
[Gimp-user] Gimp 2.8 pixelation on resize
Hi! After installing new Gimp 2.8 (on Lubuntu 14.04 64bit) for our employee, she noticed, that scanned images are going pixelated (like moire effect) much more than with previous Gimp when scaling images down. I made a little set to comparision. This is clip of original scanned (300dpi) image: http://pbrd.co/1CTKhHB This is how it looks after scaling down (Sinc algorythm) to the 51 percent http://pbrd.co/1CTKHO7 Same procedure with Gimp 2.6: http://pbrd.co/1CTL9vR And scaled down with ImageMagick: (convert -geometry 292x360 100precent.png 51percent_imagemagick.png) http://pbrd.co/1CTLgYg I like most the Gimp 2.6 version, it has no pixelation, but black characters have still sharp edges. ImageMagick is also not bad. But Gimp 2.8 version is not for my . What is wrong here? Is there something to make it better? TIA, Gunnar -- wk_ (via www.gimpusers.com/forums) ___ gimp-user-list mailing list List address:gimp-user-list@gnome.org List membership: https://mail.gnome.org/mailman/listinfo/gimp-user-list List archives: https://mail.gnome.org/archives/gimp-user-list
