Canon Line Offset Noise

Started Oct 20, 2009 | Discussions thread
ejmartin Veteran Member • Posts: 6,274
Re: The look of sharpened noise

Steen Bay wrote:

GaborSch wrote:

Steen Bay wrote:

What I meant is, that normal random noise doesn't appear as maze if sharpened

Well, here is an example, from one of the 7D raw files posted by bronxbombers, NR off, strong sharpening by DPP, 200% view:

Yes, it ain't pretty, I think we can agree about that, but Bronxbombers' 7D had this additional issue with unbalanced green gains, which confuses things a bit. I started this subthread wondering why mazing was so visible in Hulkster's 7D and (especially) 50D DPP test pics (sharpening 3, which isn't strong) at 100%, from ISO 400 and up, and I think it's (more or less) clear that the mazing must be created by the demosaicing algorytm in its attempt to maximize the amount of detail.

I agree.

Is the maze a real problem? Maybe not, it's probably just the visible effect of the compromises made in the demosaicing process, but it certainly isn't pretty at 100% view!

It's a problem in that the gain imbalance violates assumptions on which the demosaic algorithm is based. A checkerboard pattern of G values does not occur in real world images (it could only be caused by a texture at or beyond Nyquist in both vertical and horizontal directions , something quite rare in real world scenes, and would be suppressed by the AA filter anyway), so the algorithm should be allowed to assume that it will not be presented with such data. It would be nice if the demosaic algorithm is robust enough not to generate mazes, but let's put the blame for mazing where it belongs -- on the camera that generates RAW data not corresponding to any real world image.

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