Bug 148649

Summary:	DigiKam needs a better image scaler
Product:	[Applications] digikam	Reporter:	Dik Takken <kde>
Component:	ImageEditor-Canvas	Assignee:	Digikam Developers <digikam-bugs-null>
Status:	RESOLVED FIXED
Severity:	normal	CC:	caulier.gilles, qwertzmd
Priority:	NOR
Version:	0.9.2
Target Milestone:	---
Platform:	Gentoo Packages
OS:	Linux
Latest Commit:		Version Fixed In:	3.0.0
Sentry Crash Report:

Description Dik Takken 2007-08-08 21:00:49 UTC

Version:           0.9.2 (using KDE KDE 3.5.7)
Installed from:    Gentoo Packages
OS:                Linux

Large images that are downscaled to fit the window are too soft. This does not only reduce the perception of the actual level of detail in the image, but it also changes the perception of color. I don't know why the perceived color changes, but it does.

I was just comparing color managed display in both CinePaint and DigiKam. Both applications had the image scaled to fit the window. The image in CinePaint looked slightly warmer than the same image in DigiKam. I was just tearing my hair out to find the cause of the problem, and I almost submitted a bugreport about the mismatch. Also, the image in DigiKam looked relatively soft.

After applying unsharp masking on the image in DigiKam, both sharpness and color matched the CinePaint result.

It looks like the choice of scaler used for image display is more important than I would have guessed... Maybe the scaler from CinePaint can be duplicated to DigiKam?

Comment 1 Arnd Baecker 2007-11-16 08:05:00 UTC

Hi Dik,

this is really a weird effect. Do you maybe still have the examples
around, it might illustrative to attach these here.

In particular, there is another entry
http://bugs.kde.org/show_bug.cgi?id=152192
which is concerned with the image scaler, so it might
be good to have an example to take care that your case is
done properly as well.

Thanks a lot, Arnd

Comment 2 caulier.gilles 2008-03-18 12:15:28 UTC

Arnd,

This entry still valid ?

Gilles Caulier

Comment 3 Arnd Baecker 2008-03-18 12:35:39 UTC

Well, the other bug has been solved and closed. So I am optimistic,
that this is true here as well.

Dik, could you check with 0.9.3 or current svn?

Many thanks in advance, Arnd

Comment 4 Dik Takken 2008-03-22 16:48:21 UTC

I don't have my CRT available at the moment, but on my cheap LCD I see no color cast anymore.

Still, when large images are loaded in ShowFoto (using scale-to-fit), the ShowFoto image is very soft compared to Krita and CinePaint. When comparing to how GIMP displays images, I see that GIMP and ShowFoto have equally soft displays. Looks like CinePaint and Krita use different scaler, which makes your images look a lot better IMHO.

Comment 5 Dik Takken 2008-06-05 20:50:15 UTC

Ok, the color cast problem does not appear to be reproducable anymore. The image is still quite soft IMHO.

Comment 6 caulier.gilles 2009-03-25 15:41:16 UTC

Please look my post entry about this subject here :

http://www.digikam.org/node/436

Gilles Caulier

Comment 7 Dik Takken 2009-04-10 11:08:43 UTC

Ok, since I started using DigiKam on high resolution photographs (30 MP), I have come to prefer the DigiKam rendering method over GIMP and CinePaint. Without proper anti-aliasing, images don't look good when scaled down by a factor of 20 or so.

I only use CinePaint or GIMP now to check the color of the images, because color managed view in DigiKam lacks some accuracy (Bug 172196). When I use CinePaint to scale the image down to, say, 800 pixels and view it at 100%, I can accurately check the colors and brightness of the image.

Comment 8 caulier.gilles 2009-12-24 13:00:10 UTC

*** Bug 219941 has been marked as a duplicate of this bug. ***

Comment 9 caulier.gilles 2011-11-24 09:14:46 UTC

Dik, 

This entry still valid ?

Gilles Caulier

Comment 10 caulier.gilles 2012-09-11 19:53:14 UTC

Dik, no news from this entry  please ?

Giles Caulier

Comment 11 Dik Takken 2012-09-12 16:13:21 UTC

I have not seen the effect for quite a while, I assume it has been fixed.