Le mer. 12 déc. 2018 à 09:34, Björn Sozumschein <wilecoyote2...@gmail.com> a écrit :
> Hi, > > that's a really good question! I cannot understand that also, as the > comments are not very useful unfortunately.... > Is it in some way related to issue > https://redmine.darktable.org/issues/10704 > > It is possible that it is related to this issue indeed, thanks for spoting that! rawfiner > best, > Bjoern > > Am Do., 6. Dez. 2018 um 16:05 Uhr schrieb rawfiner <rawfi...@gmail.com>: > >> Hi, >> >> Looking at the code of denoise profile, I noticed a few things that seems >> strange to me concerning the anscombe transform. >> >> For wavelet codes, there is a 2x multiplier on B and R channels, while it >> is not the case for the anscombe transform of non local means: >> const float wb[3] = { // twice as many samples in green channel: >> 2.0f * piece->pipe->dsc.processed_maximum[0] * >> d->strength * (in_scale * in_scale), piece->pipe->dsc.processed_maximum[1] >> * d->strength * (in_scale * in_scale), 2.0f * >> piece->pipe->dsc.processed_maximum[2] * d->strength * (in_scale * in_scale) >> >> Why is there this multiplier? I understand from the comment that it is >> related to the fact that we have 2 times more green pixels than R or B >> pixels on a bayer sensor (note that this is not perfectly valid on xtrans >> sensor). Yet, I do not see the link between this, and the distribution of >> the poisson noise, and thus of the anscombe transform to be done. >> In addition, I do not understand why this multiplier is only here in the >> case of the wavelets process, and not here in the case of the nlmeans >> process. >> >> The second thing I noticed, is that the "processed_maximum" are all equal >> if highlight reconstruction is activated. Basically, they are equal to the >> maximum multiplier of the white balance. Thus, the anscombe transform is >> the same for R and B for instance, even though one may be much more >> "amplified" than the other. >> If highlight reconstruction is turned off, the processed_maximum values >> are equal to the white balance multipliers, so we don't get this effect. >> On images were some white balance multipliers are very different, turning >> off the highlight reconstruction results in a big change in the denoising >> (more or less equivalent to a big reduction of the force factor). >> I guess we should use piece->pipe->dsc.temperature.coeffs instead of >> piece->pipe->dsc.processed_maximum in this code. >> >> Doing this correction will allow to "copy-paste" more reliably the >> settings from one image to another, even across images that have very >> different white balance. >> Otherwise, a setting which works well on a picture with a white balance >> of (1,1,1) for instance may not work well on a picture with a white balance >> of (1, 1, 2) for instance. >> Though, correcting this will break backward compatibility. >> >> What do you think about it? >> Thanks! :-) >> rawfiner >> >> >> ___________________________________________________________________________ >> darktable developer mailing list to unsubscribe send a mail to >> darktable-dev+unsubscr...@lists.darktable.org >> > ___________________________________________________________________________ darktable developer mailing list to unsubscribe send a mail to darktable-dev+unsubscr...@lists.darktable.org
