Histogram White Spike bug in Brightness Contrast Filter dialog

[Boudewijn Rempt]

On Tuesday 30 November 2010, William Steidtmann wrote:
> Attached is a patch that eliminates the KisHistogram::KisHistogram() 
> constructor that does not pass a "bounds" parameter when using a paint 
> device, and modifies all calls to the new KisHistogram constructor that 
> does use "bounds".  Most of these calls are (temporarily) passing 
> exactBounds (and so this code does not change behaviour there), with the 
> exception of the Brightness Contrast filter, which now passes image 
> bounds, and thus fixes the White Spike bug in the Brightness Contrast 
> filter dialog.  This is very much the same as the Levels Filter 
> histogram patch (see Commit #1200357).
> 
> To recreate the (pre-patch) bug:
> 
> 1) Create a 10x10 image, 8 bit sRGB.
> 2) Set the color to a dark gray 92,92,92.
> 3) Use a pixel brush to paint all (most) of the image this dark gray.
> 4) Use menu Filter->Adjust->Brightness/Contrast curve...
> 5) Note that the graph has little or no indication (count) in the second 
> quadrant where this dark gray should be.
> 
> After the patch, the second quadrant in step 5) will have an appropriate 
> pixel count.
> 
> William Steidtmann
> 

Apart from the test that fails to compile, this patch does fix the issue. I'm wondering about the scaling of the histogram, though. The spikes are very small, barely visible.

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Boudewijn Rempt | http://www.valdyas.org
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