[Bug 24889] Moiré: Can we do anything about it?

2011-09-15 Thread bugzilla-daemon
https://bugzilla.wikimedia.org/show_bug.cgi?id=24889

--- Comment #5 from Brion Vibber br...@wikimedia.org 2011-09-15 22:55:29 UTC 
---
Created attachment 9065
  -- https://bugzilla.wikimedia.org/attachment.cgi?id=9065
Sample scale-downs using ImageMagick  gimp

Adding a Gaussian blur on the original image before scaling seems to work
wonders for this engraving; a 10x10 blur in Gimp for 310px or a 2x2 blur for
1600px both come out looking fairly smooth.

Blurring may however be relatively slow, especially on large images; it's
probably not the best idea to turn it on as a default.


However I notice I actually get very good results using ImageMagick's
'-resize' mode instead of '-thumbnail'. By default -resize applies a Mitchell
filter; I can also apply '-filter Gaussian' which looks not quite as sharp.

The -filter option seems to be ignored by -thumbnail; or if it is applied it
looks like it happens after a much more primitive resampling which'll be what
gives us the heavy moire:

http://www.imagemagick.org/Usage/resize/#thumbnail


Of course part of the reason we use -thumbnail is probably because it's fast
because it doesn't do all that filtering at full resolution. :P

Being able to flip particular images into the slower, more filtered scaling may
actually be useful -- I suspect a simple on/off will be sufficient. But I don't
know what performance impact it'll have; very large source images with high
contrast are the target group, but very large source images are the exact ones
that are slow and use lots of memory to resize. :(

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[Bug 24889] Moiré: Can we do anything about it?

2010-09-23 Thread bugzilla-daemon
https://bugzilla.wikimedia.org/show_bug.cgi?id=24889

--- Comment #4 from Derk-Jan Hartman hart...@videolan.org 2010-09-23 18:56:20 
UTC ---
http://commons.wikimedia.org/wiki/File:Rajpoots_2-scaled.tif

Another example for people who will want to work on this and test scaling
routines.

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[Bug 24889] Moiré: Can we do anything about it?

2010-08-28 Thread bugzilla-daemon
https://bugzilla.wikimedia.org/show_bug.cgi?id=24889

--- Comment #3 from Adam Cuerden cuer...@gmail.com 2010-08-28 10:15:26 UTC ---
Ah, well. Figured it was going to be something like that. 

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[Bug 24889] Moiré: Can we do anything about it?

2010-08-21 Thread bugzilla-daemon
https://bugzilla.wikimedia.org/show_bug.cgi?id=24889

--- Comment #1 from Adam Cuerden cuer...@gmail.com 2010-08-21 12:17:48 UTC ---
Note that image may be a good test: MOST thumbnails have some sort of Moiré in
the sky.

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[Bug 24889] Moiré: Can we do anything about it?

2010-08-21 Thread bugzilla-daemon
https://bugzilla.wikimedia.org/show_bug.cgi?id=24889

Derk-Jan Hartman hart...@videolan.org changed:

   What|Removed |Added

 CC||hart...@videolan.org

--- Comment #2 from Derk-Jan Hartman hart...@videolan.org 2010-08-21 12:36:29 
UTC ---
Sure, if we start scaling each image by hand, picking the best algorithm.

All is a trade off between speed, quality and sharpness. And the bigger the
image, the worse the effects can be of course.

See also: http://www.imagemagick.org/Usage/resize/#filter

Specifically: http://www.imagemagick.org/Usage/resize/#best_filter

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