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List:       imagemagick-developer
Subject:    [magick-developers] Rotation aliasing problems
From:       RT <okmot () shaw ! ca>
Date:       2003-07-29 21:02:46
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in reply to Manuel Jouglet,

>I use the bmap->rotate(degree) (ImageMagick++) in my applications and I
find
>that the result quality is poor (a lot of artefacts appears, most visibles
>are on the border of the image)
>I try to change the filter with filterType method, but it changes nothing
to
>the result as the rotate is implemented as a combination of horizontal and
>vertical shearing.
>Actually, applying 2 or three rotation destroy image quality and make it
>unusable for professional purpose.

>I wonder if I use correctly the method or if there is any way to improve
the
>quality of the rotate method.
>Do you envisage another implementation of the rotate method ?

i had the same problem of greyish edges after rotating an image.  i have a
workaround which seems to work quite well if you have the source code and
can compile your own DLL.

simply open up shear.c, locate the function BlendComposite() and change the
last line from:

composite->opacity=p->opacity;

to:

if (q->opacity == 0 || p->opacity == 0 ) composite->opacity=0;
else composite->opacity=(p->opacity>q->opacity)?q->opacity:p->opacity;

it works for me, and hope it helps you!

rt



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