>[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 
>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.

Ok, thank you, works perfectly :D

>> So what do you think i should use?
>Imagemagick. Simpler, faster and maybe even less rounding issues (it can add 
>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 have tried, but it requires more memory than i have, after 30 minutes ( with 
10 images, each of 5 Megapixels ) it was still working ( 256mb ram +768 swap ), 
whilst with gimp everything, from loading to adjusting the opacity, took only 
about 3 minutes.

>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/

I'll take a look.

Thank you!

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