Re: [Jmagick] Testing JMagick

On Thu, 28 Feb 2008, Jacob Nordfalk wrote:
>
> For those that don't know about Unit testing, the idea is to write
> some methods that use JMagick in different ways and then to compare
> the result against expected values and report an error if the results
> are not as expected. See also http://junit.org/ and
> http://junit.sourceforge.net/junit3.8.1/index.html .

I have been through this a number of times before, having written the 
test suites for ImageMagick, GraphicsMagick, and Magick++.  When 
comparing output images against a reference image, you really need to 
do a statisical comparison rather than absolute.  Otherwise 
differences between Q8/Q16/Q32 will cause test failure.  Formats like 
JPEG are lossy so they require a large "fudge factor".  I think that 
reference images should be generated using a Q8 build since they 
represent the maximum variation from the "one true image" and the 
files are likely to be smaller.  Dealing with fonts is a major problem 
since each version of FreeType produces different results, and glyph 
hinting (FreeType compile-time options) can make a huge difference in 
the output.  There are similar problems with PDF and Postscript.

Bob
======================================
Bob Friesenhahn
[bfriesen@masked-domain], http://www.simplesystems.org/users/bfriesen/
GraphicsMagick Maintainer,    http://www.GraphicsMagick.org/

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