ImageItem crashes in getHostogram()

[Erik J]

Hi everyone,

I am using a HistogramLutWidget for an image that is displayed in a pg.GraphicsLayoutWidget. The image is a dark and gain corrected image from a CCD camera that updates in real time as it is received from the camera. The problem I am having is that the ImageItem in the histogram display will crash periodically in the method getHistogram(). This occurs if the min and max of the image are the same. Here is the code snippet from getHistogram:

        if bins == 'auto':

            if stepData.dtype.kind in "ui":

                mn = stepData.min()

                mx = stepData.max()

                step = np.ceil((mx-mn) / 500.)

                bins = np.arange(mn, mx+1.01*step, step, dtype=np.int)

                if len(bins) == 0:

                    bins = [mn, mx]

            else:

                bins = 500

If mn and mx are equal, then np.arange() fails with an error. I suggest the following code change to fix the problem:

        if bins == 'auto':

            if stepData.dtype.kind in "ui":

                mn = stepData.min()

                mx = stepData.max()

                step = np.ceil((mx-mn) / 500.)

                bins = np.arange(mn, mx+1.01*step, step, dtype=np.int)

                if len(bins) == 0:

                    bins = [mn, mx]

            else:

                bins = 500

[Erik J]

Sorry, somehow this got posted before I was finished. The new code should be:

        if bins == 'auto':
            if stepData.dtype.kind in "ui":
                mn = stepData.min()
                mx = stepData.max()
                step = np.ceil((mx-mn) / 500.)

                if step == 0: step = 1.0

                bins = np.arange(mn, mx+1.01*step, step, dtype=np.int)
                if len(bins) == 0:
                    bins = [mn, mx]
            else:
                bins = 500

Please let me know if anyone else has experienced this problem. It can easily occur if an image is saturated or if nearly all the pixels are zero.

Thanks,

Erik

 

[Kenneth Lyons]

Hi Erik, I believe this is the same issue reported here: https://github.com/pyqtgraph/pyqtgraph/issues/1033

The comments there are still accurate (fixed version not released yet), but there are instructions for installing pyqtgraph via git.

Hope that helps.

- Kenny

[Erik Johansson]

Thanks, Kenny! That indeed is the same problem. The mx+= 1 fix you implemented looks fine to me. Thanks for the help.

Erik

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************************************************
Erik Johansson
Project Manager, Wavefront Correction System
National Solar Observatory
Daniel K Inouye Solar Telescope
3665 Discovery Drive, Boulder, CO 80303
Tel: 303-735-7723
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