Hi, [EMAIL PROTECTED] (2007-11-24 at 1903.37 -0000): > > I'm trying to reduce noise using multiple photos of the very same subject, > using both a tripod or simply repeating a scan a number of times ( i have a > flatbed scanner with a lot of noise especially in dark areas... ) [...] > I have used the first level, as normal, with 100% opacity, then i have added > other 9 levels ( 9 photos ), with opacity 100/9=11,1, and mode set to normal. > > If i use 10 levels, at 10% opacity each one, the brightness of the result is > different from the original ( lighter ).
The trick for mixing this way is that the N layer has to be set to 1/N opacity. The reasoning is that the N layer will contribute that factor, and the rest ((N-1)/N) has to come from the previous mixed layers, so the result always totals 100% ((1 + N-1)/N). First (base) layer 1/1 -> 100%, second layer (the one just above base) 1/2 -> 50% (and the other 50% comes from the first), third layer 1/3 -> 33.33% (and the other 66.66% comes from the 1 and 2) and so on. This approach will probably have rounding errors. > So what do you think i should use? Imagemagick. Simpler, faster and maybe even less rounding issues (it can add all images at once, then do a single multiply by 1/N, at least that is how I would code such op). :] convert image1.png ... imageN.png -average result.png I investigated the topic for mixing different frames time ago to create more film like renders (lots of other things in the trick, but finding a fast and nice average op was one of the core issues I had to solve): http://www.infernal-iceberg.com/blender/mblur/ GSR _______________________________________________ Gimp-user mailing list [email protected] https://lists.XCF.Berkeley.EDU/mailman/listinfo/gimp-user
