[Numpy-discussion] Downsampling array, retaining min and max values in window

Hi there, I have a large array, lets say 40000 * 512, which I need to downsample by a factor of 4 in the y direction, by factor 3 in the x direction, so that my resulting arrays are 10000 * 170 (or 171 this does not matter very much) - but of all the values I will need to retain in the downsampled arrays the minimum and maximum of the original data, rather than computing an average or just picking every third/fourth value in the array. So essentially I have a 4*3 window, for which I need the min and max in this window, and store the result of applying this window to the original array as my results. What is the best way to do this? Regards Ludwig