28 January 2008 Digital image improvement by adding noise: an example by a professional photographer
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To overcome shortcomings of digital image, or to reproduce grain of traditional silver halide photographs, some photographers add noise (grain) to digital image. In an effort to find a factor of preferable noise, we analyzed how a professional photographer introduces noise into B&W digital images and found two noticeable characteristics: 1) there is more noise in mid-tones, gradually decreasing in highlights and shadows toward the ends of tonal range, and 2) histograms in highlights are skewed toward shadows and vice versa, while almost symmetrical in mid-tones. Next, we examined whether the professional's noise could be reproduced. The symmetrical histograms were approximated by Gaussian distribution and skewed ones by chi-square distribution. The images on which the noise was reproduced were judged by the professional himself to be satisfactory enough. As the professional said he added the noise so that "it looked like the grain of B&W gelatin silver photographs," we compared the two kinds of noise and found they have in common: 1) more noise in mid-tones but almost none in brightest highlights and deepest shadows, and 2) asymmetrical histograms in highlights and shadows. We think these common characteristics might be one condition for "good" noise.
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Takehito Kurihara, Yoshitsugu Manabe, Naokazu Aoki, and Hiroyuki Kobayashi "Digital image improvement by adding noise: an example by a professional photographer", Proc. SPIE 6808, Image Quality and System Performance V, 68080R (28 January 2008); doi: 10.1117/12.766310; https://doi.org/10.1117/12.766310


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