On Mon, Apr 9, 2018 at 7:09 AM, Matthieu Moy <[email protected]> wrote:
> ----- Original Message ----- > > From: "Chris" <[email protected]> > > > Seems as though the pink colours appear in my image when I disable > 'highlight > > reconstruction'. > > Yes, this is expected. The module is precisely here to remove this pink > color. > > > With this disabled the Green & Blue channels have a lot less > > data in the highlights than the red. Enable highlight recon, and it > seems to > > scale all the RGB to a simple range. > > The problem is the following: > > * All channels (R, G, B) are initially coded on a range, say [0, 2^14-1] > for a 14-bits sensor RAW image. Channels that clip have the value 2^14-1 > (well, I'm slightly oversimplifying because saturation of the DAC comes a > bit before this value, but ...). > > * The white balance module scales each channels, and usually scales the > green channel less than the other. So the clipped pixels won't have the > same values on R, G and B anymore after white balance. So, blown out areas > are not white/grey anymore, they have color. > > The "highlight reconstruction" module does two things after that: > > * Desaturate the blown-out areas (done for all modes of the module) > > * Optionally, try to recover details. The default mode does not try that, > it just clips highlights and turn them into plain white (which may become > grey if you apply a negative exposure compensation). The "Reconstruct in > LCh" is quite good to recover details when at least one channel is not > clipped (e.g R and B are clipped, you can't expect much on colors, but the > G channels can be used to recover an L channel). "Reconstruct color" does > more or less the same, but works well on different images. > > In any case, setting the "clipping threshold" to 2.0 means the module will > only work on pixels that have an L value 2 times greater than the clipping > threshold. Which in practice means that the module will have no effect. The > manual says "The default is usually satisfactory without any need for > additional adjustments", which in dt is usually to be read as "There's no > reason for you to change this value, but it's a parameter that appears in > the internal algorithms so we've exposed it to the user just in case". > My experience with clipping threshold was different, at least on this dng. Setting it to 2.0 allowed me to recover the cloud data and come up with a pretty close match to what Chris achieved using LR. Result is here https://www.dropbox.com/s/lrg8wix996e6k2f/_MG_1496.jpg?dl=0 > > > Odd, because I do not get this pink appear when I reduce the highlights > in > > Lightroom... and I am still using this same .dng file. > > I never used Lightroom, but from what I've read, LR's philosophy is to do > a bit of processing automatically (or "behind your back", depending on the > point of view). OTOH, dt makes almost everything explicit, and gives you > control on everything, including settings that are not really meant to be > changed. You may or may not like it, but it's unlikely to change ;-). > > The pink was there in the RAW (after white balance), LR just removed it > for you. > > -- > Matthieu Moy > https://matthieu-moy.fr/ > ____________________________________________________________ > ________________ > darktable user mailing list > to unsubscribe send a mail to darktable-user+unsubscribe@ > lists.darktable.org > > Bill ____________________________________________________________________________ darktable user mailing list to unsubscribe send a mail to [email protected]
