5D3 Pattern Noise Improvement and High ISO Cooking

Started Apr 1, 2012 | Discussions thread
Press Correspondent
Press Correspondent Veteran Member • Posts: 3,345
Two types of impact

Kabe Luna wrote:

Bill, what is the practical impact of your findings here? I just take photos, and am interested to know how (positively or adversely) this might affect my photography.

FFT, if done properly, is completely reversible. If the image with banding is converted using FFT and you see rhe tick marks that represent banding, and you carefully erase them, then the image restored back by the reverse FFT conversion should no longer contain banding. FFT is a common method of reducing white noise like grain and pattern noise like moire in scanned newspaper or magazine images.

The corcle in the ISO 100k image shows that Canon artificially reduces resolution at this ISO. I believe, they also do it at ISO 50k. FFT effectively splits the image into larger and smaller details. The larger ones go to the center, the smaller go to the edges. The circle means that Canon cuts the smaller details out as a form of noise reduction. This is sort of unfortunate, as downsampling may produce better results, because, while resolution is similarly decreased, noise becomes statistically smaller due to its random nature. Plus you could still apply any further noise reduction after that. This still could be done by underexposing at ISO 25k and then downsampling. The ISO 50k and 100k are extended, meaning they really are ISO 25k digitally amplified and processed in the camera.

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