[Libreoffice-qa] [PUSHED] Re: [PUSHED] Re: [PATCH] fdo#46378: Poor Resampling Image quality

Tomaž Vajngerl quikee at gmail.com
Wed Jun 6 14:22:00 PDT 2012


On Tue, Jun 5, 2012 at 11:33 AM, Jan Holesovsky <kendy at suse.cz> wrote:
> Great stuff - I have pushed your patch, and also my patches to default
> to Lanczos filter.  Can you please add an example of "before" and
> "after" where the advantages of the Lanzcos filter are nicely visible to
> the Release Notes (http://wiki.documentfoundation.org/ReleaseNotes/3.6)?

> Adding the QA list to the CC: - thanks to Tomaz, we have changed the
> default of the image resize operations to a new scaling operation.
> Please be careful about bugs that involve scaling of images, quality of
> eg. PDF output, or speed of such operations.
Regarding bugs.. I have found a problem with creation of Bitmaps in
ImplScaleLanczos. I have fixed so the Bitmaps are created in the same
way as in ImplScaleInterpolate - the patch is attached. This problem
is visible if you go into impress and set the background of a slide to
a bitmap which is tiled. I have not found any reports in bugzilla
about this yet.

> Tomaz - what interests you next? :-)  You've already outlined some ideas
> regarding the filters, correct?
I am working now to on blur/soften filter which uses
ImplHorizontalConvolution and ImplVerticalConvolution - which are also
used in Lanczos resampling. I have this already working with a
parameterized blur radius. Currently the soften filter only uses a
fixed 3x3 convolution matrix with 2D convolution algorithm. My
solution should be faster and more flexible than the current one. I
still need to add a dialog to select the blur radius which I will do
in step 2.

Other ideas I have is to add "reduce image resolution" function
directly to bitmap so a user could change the image resolution not
only in PDF export but in general. When a user applies a filter, the
image is changed and saved as a new PNG image into the document. So to
create something like this should not be hard.

In a long run I want to improve the quality of images in export but I
think this is a problem of whole page rendering and not so simple to

Regards, Tomaž
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