[magick-users] What's the command line equal blur of ResizeImage in C API

[Anthony Thyssen]

On Wed, 25 Feb 2009 22:44:10 +0800
Jiang Miao <jiangfriend at gmail.com> wrote:

| According C API ResizeImage
| http://www.imagemagick.org/api/resize.php
| There is a parameter blur,(the blur factor where > 1 is blurry, < 1 is
| sharp. Typically set this to 1.0.)
| how can I do that through command line 'convert' ?
| if use sharpen or blur, when the value of blur of ResizeImage is 0.8,
| what's the value should be set on -sharpen?
| 
That is an old and even miss-named setting!!!!

See the updated notes in IM Examples, Resize, Filters
  http://www.imagemagick.org/Usage/resize/#filters

Also see the specific notes on the 'blur' expert setting that is really
only useful to control gaussian like filters...
   http://www.imagemagick.org/Usage/resize/#filter_blur

This documentation not only tells you how to use the setting but exactly
what the setting does in terms of the re-sampling filter.

I also recommend you read the section before filters on Resize Artifacts
   http://www.imagemagick.org/Usage/resize/#artifacts
before hand so that you get a better idea of the terms and what filters
are attempting to do.

For a cleaner gaussian-like filter, that does not have the 'support cut-off'
use a 'Quadratic' or 'Cubic' filters.  See
   http://www.imagemagick.org/Usage/resize/#filter_support
for details. of this.

Basically if you need to use expert settings, then you are probably not
doing things right! Or attempting to do something special.

Most people use a normal resize then use a unsharp filter or adaptive
sharpening for improving edge sharpening.

ASIDE:
Before v6.3.6-3, IM made the grave mistake of actually using the
sinc windowing function directly as a filter weighting function. This
in turn caused all these filters to produce rather badly aliased images,
when used for resizing. As a consequence the filters were often
mis-understood or rarely used. This has now been fixed.



  Anthony Thyssen ( System Programmer )    <A.Thyssen at griffith.edu.au>
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           Beware the kite eating trees!  -- Charlie Brown
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