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I'm playing with CIImage and CIFilter to create some custom image processing. I'm on macOS 10.13.6 and using XCode 10.1.I can't work out this problem... the CIAreaMinimum and CIAreaMaximum filters (that return a single pixel image with the max/min colors from the CIImage) don't always produce a sensible output.It seems that for any PNG image with transparency (first read into a CGImage, and using this to create a CIImage), the max is always black and the min is always white. For any other image (including other PNGs), it seems to produce expected results.If I can't get this working, an alternative is for me to write a custom CIFilter (since I need some other custom stuff anyway), in which case how do I, in the first instance, go about make my own max/min filter?I'm guessing I need a way to store min/max values, and then for each pixel sample check the min/max against the pixel value and update the min/max when appropriate, but how do I create such a persistent value to pass in/out of the custom CIFilter using Core Image Kernel Language (not Metal) and Swift?