Abstract: An x-ray or gamma ray image that is produced as an array of pixels is treated for reduction or elimination of white spot noise. Two or more successive images in registry are produced and the pixel values at each pixel location are inspected for the respective images. The pixel values are considered according to rank, e.g. from dark to bright, and the lowest ranking pixel value is selected for each pixel location. This creates an output image that is substantially free of the spot noise that results from direct impingement of the x-ray photons on the imaging device. This technique is especially useful in portal imaging for radiation therapy, dental imaging, or industrial imaging.