ComputeHistogram does not seem to take into account the SourceRectangle.

[rolandsmeenk]

I ran into an issue where I wanted to calculate a histogram of only a part of a CanvasImage, but it looks like the SourceRectangle is not taken into account. If I set it to something different than the rectangle returned by GetBounds the results look always the same. Is this expected behaviour?

I the meantime I will render the parts of interest to a separate rendertarget so their histograms can be calculated separately.

[shawnhar]

The source rectangle parameter to ComputeHistogram works as expected in my tests.

Please provide a repro app that shows the problem you are seeing.

[rolandsmeenk]

Ok, here's a little UWP app. Use the slider to scale the SourceRectangle and notice that the drawn histograms do not change.
HistogramTest.zip

[shawnhar]

Thanks for the repro - we'll take a look.

[shawnhar]

Confirmed this is a bug in Win2D.

As a workaround until we are able to get this fixed, you can feed your image through a CropEffect to specify what region you want, then pass that CropEffect into ComputeHistogram.

[rolandsmeenk]

Ok, thanks for the confirmation.

[shawnhar]

This is fixed in Win2D 1.21.0 (released today)