Re: [matplotlib-devel] A new KNOWNFAIL, pcolormesh.png ?

[Paul Ivanov]

Sandro Tosi, on 2011-01-18 19:29,  wrote:
> Hi,
> 
> On Tue, Jan 18, 2011 at 15:00, Michael Droettboom <md...@stsci.edu> wrote:
> > I'm not sure PIL enters into it -- there shouldn't be any code path
> > involving PIL in that case.
> >
> > I think this a case where the image comparison tolerance needs to be
> > increased.  You would do this be passing a "tol" parameter to the
> > image_comparison decorator on the pcolormesh test.  The default is 1e-3,
> > but it should be conservatively increased until the test passes.  You
> > can perform this experiment yourself, or attach the result image for the
> > test to this list and I can experiment to find a correct value.
> 
> I'm attaching the images, just for reference; as you can see, the
> difference is very tiny and with a tolerance of 0.02 I was able to
> pass the test (RMS Value: 0.0116511801977).

I just wanted to chime in that there *is* structure in the
differences between the images - which don't show up on screens
which don't have linearized gamma (the difference between 0 and 1
are much smaller in brightness than the difference between 127
and 128, for example).

A quick way to get around this is to just invert the colors.

in X11, I do this with 'xcalib -a -i' which toggles back to
normal if you run the command twice (Compiz also has it's own
version of this via some keyboard shortcut, IIRC, but I don't use
it). ImageMagick's convert can do this with the -negate flag. On
OS X, there's something like command-F8 to do this.  

For completeness, if you're interested in doing this in
matplotlib, ;) just subtract your (floating point 0.0-1.0) color
from (1.,1.,1.) to get the new color.

I'm attaching the difference image, with its colors inverted.

best,
-- 
Paul Ivanov
314 address only used for lists,  off-list direct email at:
http://pirsquared.org | GPG/PGP key id: 0x0F3E28F7 

<<attachment: failed-diff-expected-pcolormesh-inverted.png>>

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