[Bug 152192] New: resize really bad qualitatively

[Gilles Caulier-4]

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------- Additional Comments From caulier.gilles gmail com  2007-11-16 10:41 -------
SVN commit 737465 by cgilles:

add warning message on dialog about resize Restoration Mode
CCBUGS: 152192


 M  +26 -18    imageresize.cpp  


WebSVN link: http://websvn.kde.org/?view=rev&revision=737465
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[Gilles Caulier-4]

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------- Additional Comments From caulier.gilles gmail com  2007-11-18 09:17 -------
To everybody witch use svn version of digiKam (KDE3 branch):

Please test again. no resize tool use a bicubic interpolation instead a simple linear interpolation (from CImg library)

Please give me a feedback. If all is fine now, this file will be closed...

Thanks in advance

Gilles Caulier
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[Arnd Baecker]

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------- Additional Comments From arnd.baecker web de  2007-11-18 10:22 -------
Gilles, nothing is fine for me, see c#16.
Does it work for you (taking the original example and scale down to 200x300,
looks really bad!)
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[Gilles Caulier-4]

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------- Additional Comments From caulier.gilles gmail com  2007-11-19 11:31 -------
Arnd,

Yes, it still bad. I have tried to play with all parameter from CImg::resize(), but without better result.

Sound like a bug in CImg. I need to find another way to solve this problem

Gilles
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[Gilles Caulier-4]

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------- Additional Comments From caulier.gilles gmail com  2007-11-19 11:49 -------
ok, this is the issue of this file: using DigiKam::DImg::resize() method witch use smoothScale algorithm (imlib2). Result is very similar than Gimp.

I will attach few images resized with different algorithm to compare.

And of course, i will commit changes in svn...

Gilles
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[Gilles Caulier-4]

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------- Additional Comments From caulier.gilles gmail com  2007-11-19 11:54 -------
Created an attachment (id=22116)
 --> (http://bugs.kde.org/attachment.cgi?id=22116&action=view)
Resized image using CImg::resize and bi-cubic interpolation
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[Gilles Caulier-4]

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------- Additional Comments From caulier.gilles gmail com  2007-11-19 11:54 -------
Created an attachment (id=22117)
 --> (http://bugs.kde.org/attachment.cgi?id=22117&action=view)
Resized image using CImg::resize and linear interpolation
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[Gilles Caulier-4]

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------- Additional Comments From caulier.gilles gmail com  2007-11-19 11:55 -------
Created an attachment (id=22118)
 --> (http://bugs.kde.org/attachment.cgi?id=22118&action=view)
Resized image using Gimp and linear interpolation
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[Gilles Caulier-4]

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------- Additional Comments From caulier.gilles gmail com  2007-11-19 11:56 -------
Created an attachment (id=22119)
 --> (http://bugs.kde.org/attachment.cgi?id=22119&action=view)
Resized image using Digikam::DImg::resize (modified smoothScale algorithm from
imlib2 to support 16 bits color depth)
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[Gilles Caulier-4]

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------- Additional Comments From caulier.gilles gmail com  2007-11-19 11:57 -------
Note : the original image is a PNG file using 16 bits color depth:

http://digikam3rdparty.free.fr/TEST_IMAGES/PNG/5-16bits-photo.png

gilles
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[Gilles Caulier-4]

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------- Additional Comments From caulier.gilles gmail com  2007-11-19 12:10 -------
SVN commit 738645 by cgilles:

digiKam from KDE3 branch : With Simple resize mode, use DImg::resize() intead CImg::resize() to have the most image quality result.
CCBUGS: 152192


 M  +29 -21    imageresize.cpp  


WebSVN link: http://websvn.kde.org/?view=rev&revision=738645
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[Gilles Caulier-4]

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caulier.gilles gmail com changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|                            |FIXED



------- Additional Comments From caulier.gilles gmail com  2007-11-19 12:28 -------
SVN commit 738655 by cgilles:

backport commits #738645 from KDE3 branch
BUG: 152192


 M  +42 -32    imageresize.cpp  


WebSVN link: http://websvn.kde.org/?view=rev&revision=738655
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[Cristian Tibirna]

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------- Additional Comments From tibirna kde org  2007-11-19 12:46 -------
This is most excellent. Thank you.
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[Gilles Caulier-4]

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------- Additional Comments From caulier.gilles gmail com  2007-11-21 09:54 -------
To be clean in digiKam code about CImg, i have contacted David Tschumperlé (Cimg author) to have tips around this problem.

Sound like we cannot use directly a simple CImg::resize(), but an iteration of progressive half resizements :

void GreycstorationIface::simpleResize()
{
    const unsigned int method = 3;      // Initial estimate (0, none, 1=block, 3=linear, 4=grid, 5=bicubic).

    int w = m_destImage.width();
    int h = m_destImage.height();

    while (d->img.dimx() > 2*w &&
           d->img.dimy() > 2*h)
    {
        d->img.resize_halfXY();
    }

    d->img.resize(w, h, -100, -100, method);
}

I have patched my Digikam::CImg interface and now result is similar than others algorithm...

Gilles... Who love clean code (:=)))
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------- Additional Comments From mikmach wp pl  2007-11-21 18:11 -------
I wonder if it would be possible to put weak unsharp mask sharpening
between each resize. This is the best way to get good resize results,
especially big ones. Resize, USM (radius 1, amount - something small,
eg. 40%, threshold - 0 or 0.05 (when max is 1)), repeat.

OTOH this may be rather task for new batch queue editor.
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[Cristian Tibirna]

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------- Additional Comments From tibirna kde org  2007-11-22 14:39 -------
Re #33. I don't think so. Sharpening is a creative choice. But I think this is a thing to experiment with in the realm of configurable "advanced" resize, the kind that CImg offers if you choose to "restore image (slow)"  ;-)
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[Cristian Tibirna]

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------- Additional Comments From tibirna kde org  2007-11-22 14:44 -------
Bonjour Gilles, thanks again for the great work.

Concerning #32, I'd compare the two methods before preferring clean code to good result code. The cimg-based method you describe in #32 might give still unsatisfying results because of blurring. I didn't try the code in my local digikam sources to thoroughly test, but I tried a few consecutive 50% resizes and the final image, while less jagged, is much more blurred than the screen-zoomed image. Thus, once again, the screen-zooming algorithm seems to be better than what cimg has to offer. So, just a bit of warning, if allowed...

Thanks again.
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[Gilles Caulier-4]

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------- Additional Comments From caulier.gilles gmail com  2007-11-22 15:05 -------
Christian,

Don't be afraid, digiKam still to use the screen-zooming algorithm (imlib2 based + 16 bits color depth support). It more fast.

I have just patched the code in digiKam CImg interface to have a code ready to use in the future...if necessary.

Gilles
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------- Additional Comments From kamil.stepinski gmail com  2008-03-16 11:26 -------
Guys,

The image resizing quality is _really bad_ in digiKam (I have 0.9.2 installed).
It's so bad that the output is just unacceptable for me. :(

I really think you should add a selection box with a few algorithms (Hermite, Mitchell, Lanczos, etc.) with Lanczos as a default one because it provides the best results.
Currently I'm resizing all pictures with IrfanView (runs well with Wine) and the rest of postprocessing is done in digiKam. It's not the most convenient method but it works.
I think you should consider the current resize quality as a major issue - as it is a tool that is used very frequently.

Here's the link to the example of the resize quality comparison:

http://picasaweb.google.com/kamil.stepinski/Digikam/photo#5178275271094829746

Please observe car window edges.

1 - digiKam 0.9.2 to the left, IrfanView 4.10 to the right
2 - resizing from 5Mpix camera to 800x600, IrfanView is using Lanczos filter, digiKam is using I-don't-know-what.

That's the only major problem I have with digiKam. I think the resize has been working much better in 0.8.x version.

At the end -> Thanks guys for the great piece of software! The applications is really great!
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[Gilles Caulier-4]

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------- Additional Comments From caulier.gilles gmail com  2008-03-16 11:37 -------
Kamil,

This problem have been fixed with 0.9.3 release. Please update digiKam....

Gilles Caulier
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