Originally Posted by Torsten Kaiser
[font="Tahoma"]During De-Graining (in most tools) the grain texture is sampled and through various algorythm methods rendered in either a smaller size of the grain or re-rendered at lower frequency. Spatial median filters are often used in this environment, the problem is that if "overdone" the image looks practically grain free and dull. Some cleanup tools, by the way, use a similar method.
So these tools would be specifically for grain and not other 'random noise', right? Are these tools currently using mostly intraframe filtering or is there also interframe filtering (temporal filtering) applied? Lowry uses temporal filtering, as far as I know.
During De-Noising the whole image is being sampled for anything that is in the high frequency range (thus also affecting, depending on the intensity, more or less the sharpness and detail) and rather indiscriminately "wiped clean". The effect, however, grows with intensity to a clearly visible dither, leaving distracting patterns (similar to dithers in PS and other software for GIF file reduction) behind. What's left is then a flat image with little depth and very simplified colors and a demolished texture.
So tools looking for special random noise that is not grain would be listed here (such as scratch removal, speckle removal, dust busting) or is that a third category? If this is a third category I don't quite see the point of this category. If you can't tell apart HF detail that is real detail and HF detail that is noise and just filter it you got a rather crude tool. If you want HF detail in general gone use a low pass filter. Or is this category for general real noise that is none of the special correlated kinds (grain, scratches etc.)? Or every noise that is not grain?