A quite timely question for me, I just finished implementing the Duiker filmic curve in my hack software…
It became evident to me about a year ago that I needed more fine-grained control of a tone curve with high-bitdepth image data. Looking at most raw histograms of unscaled data, it is predominant to see most of the data over at the left. Indeed, if you can zoom in on the histogram, you find that a lot of tonality sits in the first 256 values of a 16-bit raw image (libraw delivers unmodified raw data as unsigned 16-bit integers), which on the display scale from 0=black to 255=white of an 8-bit JPEG output is all under the first tone value above 0. So, you want your tone curve to “curve” in that range, in order to control your shadows.
An interactive tone curve won’t give you any real control in that range. Mine works on a 0.0-255.0 floating point scale, which will allow me to scale into the really low region, but not with any really useful slope. I toyed a bit with “zoom” implementations, but I just really couldn’t warm to encoding all the relevant parameters in the output image (.pp3 or xmp sidecar files, in other softwares)
Well, this is what a filmic curve does that none of the other tone curves address: it puts a “toe” in the very bottom of the data range, one that transitions the black values gradually into the main part of the curve. John Hable’s blog post describes it very well:
In the post, he has a couple of graphs that show that toe in relation to the rest of the curve. Looking at the whole curve, you can’t see it, but if you magnify down toward the origin, it becomes quite evident.
Here’s the so-called Duiker filmic transfer function, from Hable’s post:
For simple control of the toe, the 0.5 coefficient can be decremented toward 0.0 to increase decrease (oops…) the toe slope and push the toe down to the axis, which will increasingly crush those low tones:
Going the other direction pulls the shadows up, to the point where the curve starts looking like any other “regular” power or log curve.
I’ve been messing with this very coefficient with a recent flower image that has a dark background, and it is simply amazing the amount of control it has over how those shadow tones are scaled. Right now, I’m without any computer that has either this image or my software, so all I can do is show Excel graphs.
I haven’t messed with the shoulder yet, but it appears the 1.7 coefficient influences it.
Note that @Carmelo_DrRaw’s recent Photoflow work is a more intuitive approach to filmic, in that the controls over the toe and shoulder are more specific in both dimensions:
I’m thinking in @darix’s terms, just use filmic all the time. But I think the display ICC tone transform needs to be nullified, let filmic do that work, but I don’t have the tools with me to mess with that right now…