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
