The different filters do have marked effects on the quality estimate. Starting from the top row we have a quality filter set at 1,5 and 15 pixels. The spectrum image on the left shows what the filter does with an individual image. When set at 1, most of the values are right of the filter and hence the quality is estimated at 0.59. The corresponding graph at the right that shows the quality difference (red line) for all the images (ordered by quality) shows little or no difference in the sequence. Read further below

Now the quality filter was set at 5 pixels and the difference in image quality has become clearer. This is even more so with the filter set to 15 pixels. A clear set of images is now designated to be the “best” and other are considered far poorer ... lets see at the
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