Mike Chaney's Tech Corner
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Author Topic: Wavelet De-noising in DCRAW  (Read 8169 times)
djwarner
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« on: June 27, 2009, 01:37:19 PM »

Recently, I have been working with HDR images and various software products to merge multiple exposures into one HDR image. One problem is that a lot of Chroma noise gets introduced with these conversions. My SLR/n is notoriously noisy in the shadows before the conversions.

I began thinking about how much of the improvement in the current generation of DSLRs was physics and how much was software. Then I discovered that DCRAW has a "wavelet de-noising" capability - but none of the current generation HDR software using DCRAW as a front-end utilize this feature - or at least they provide no control for it. DCRAW also has a median filter that will also reduce chroma noise.

I think this noise control should be particularly interesting since it works on the linear raw image before applying any tone curve.

I finally found a current binary of DCRAW compiled with a Microsoft C compiler that would run on my Vista 64 platform. Running in batch mode, I found the wavelet de-noising to be quite good at eliminating noise. Perhaps as good as anything else I've seen.   

Have you any experience with this feature in DCRAW.

The other question I have concerns custom white balances. I have SLR/n .ICM files for tone curve, daylight, tungsten, and fluorescent lighting. But DCRAW does not want to accept them. Do you have any magic tricks?
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« Reply #1 on: June 27, 2009, 01:55:33 PM »

I tried the wavelet NR in dcraw and found it very disappointing.  If you set it to any level that really reduced noise, it smudged over so much detail that the image looked like a finger painting.  Set it lower and it was ineffective.  Since I felt the existing NR in Qimage (in the raw format options) worked much better, I never implemented a "link" to the wavelet NR in dcraw.

Mike
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