Paul Rubin wrote: > John Doty <[EMAIL PROTECTED]> writes: >> I have a bunch of image files in FITS format. For each raster row in >> each file, I need to determine the median pixel value and subtract it >> from all of the pixels in that row, and then write out the results as >> new FITS files. > > I dunno what FITS is, but if you have a list of pixel values, that > calculation sounds like two lines: > > median = sorted(pixels)[len(pixels)//2] > new_pixels = [p-median for p in pixels]
Yes. The efficient exact algorithms for this problem use *partial* sorts. The Forth one from the FSL is of this class (although I know of two better ones for big arrays). But it's tough to beat the efficiency of the approximate histogram-based method the Python stats module implements. -- John Doty, Noqsi Aerospace, Ltd. -- Specialization is for robots. -- http://mail.python.org/mailman/listinfo/python-list
