The “recent” modules, sigmoid and filmic, achieve something beyond simply transforming from scene to display referred. Once well understood, they encourage me to get out there and take photos, with the knowledge that I have a fairer opportunity of coming back to the computer, with much more control than was possible with the base curve.
I am uncomfortable with comparing sigmoid and filmic, but its difficult to describe one without referring to the other, like if everything were blue, it would be difficult to describe. White only makes sense if there is something else to compare it with.
Because these two modules have different controls, its also impossible to actually compare them, cos if you had all the time in the world, maybe you could come up with settings that would make an image almost indistinguishable from the other. So any statements of a trend, are based on how each module “pushes” me to use them, and make adjustments with them, and the result thereof. Your mileage may vary, from mine. These opinions are not based on the default settings, but on how I have tended to make changes from the defaults.
From recent images, my opinions, from trends that have developed in my use of them are :
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sigmoid tends to deliver images which pushes aspects of the image more into the extremes - dark and bright, leaving less information in the mid-range. So you get more contrast broadly speaking.
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sigmoid also tends to deliver images where there is less separation between colours, pushing shades of yellow and orange nearer to each other, and in greens you get less of a separation between the various greens. It is the same with other colours, but in the examples I have posted here, the predominant colours are the yellows and greens.
If there was one wish for sigmoid, it would be one more control (ideally three or four), so one could control the contrast globally, with another set of three controls to manage this contrast with more control, in the shadows, midtones and highlights. Maybe we are now stepping on the toes of other modules in dt. But I did check and to the best of my knowledge there is no other module which gives you control over contrast in shadows, midtones and highlights distinctly. I make the layman’s assumption, as I am only an end user in this case, not a physics professional, that the chroma observation, which I mentioned in 2 above, will also be adjusted by these controls, so you can have more or less separation of colours, globally or in shadows, midtones, and highlights when the luma contrast is adjusted.
Then there will be introduced another challenge, adding controls to adjust the crossover between the shadows and midtones, and between midtones and highlights.
Then one more wish, 3 controls more controls to adjust the luma (darker or brighter) in the shadows, midtones and highlights. Note, I have not asked for a global control of luma, as this is already included in the exposure module, and ideally should not be duplicated, elsewhere.
To the casual observer, unless you had the images side-by-side, you may not be able to tell any difference. Broadly speaking this gives the current sigmoid images a bolder, more vivid look, more binary, monochromatic, which lends itself well to certain kinds of images, where the colours look more like the result of reducing luminance via the “color balance rgb” module. Greens are darker, yellows are darker. Somewhat like the effect of having used the local contrast module.
Sigmoid–
Filmic–
I thought it good to express this via curves, cos some of this could be simulated via curves also.
If you had two fixed points for the transition between shadows and mids, and between mid tones and highlights, its possible to then use three other points on the curve to modify the dynamic range of each of the three regions. I’ve used curves only to hopefully make it easier for you to understand what I had written earlier. I do not have the mathematics skills to fully describe the additional controls which you may wish to consider. Curves may make it easier to convey what I mean.
Curve example. compressing dynamic range in each region.
Curve example, lifting the shadows only. all other regions have no change.
Curve example lifting only the mid-tones.
Of course in an ideal implementation these mid points will not remain on the linear line, but will have some “latitude” to move up or down, with changes made in each region, leading to two other possible controls. So that’s 8 controls in total described below.
This introduces the potential for what I call a super highlights region a 4th. Typically the brightest whites or light/bright colours
- to set the transition point between shadows and mid tones.
- To set the transition point between mid-tones and highlights.
- To set the transition point between highlights and super highlights.
- Adjust gradient up or down, in shadows (i.e lift shadows, or crush blacks more)
- Adjust gradient up or down in midtones ( less contrast - brighter, or more contrast - )
- Adjust gradient up or down in highlights.
- Adjust gradient up or down in superhighlights up or down.
- Adjust gradient globally, to make it more or less contrasty.
- Adjust latitude of transition points, i.e how far up or down they are allowed to deviate from the set position, when local adjustments of gradient in the 4 regions are modified.
I can imaging this sound really like a lot. But I have come to accept - this is the mindset of darktable and the darktable developers - more control not less. So rather than me try to simplify things, why not fully explore it to create something that is quite flexible, even though novices may find it difficult to comprehend, at first.