darktable offers multiple modules for adjusting image contrast, and I’m getting a little confused as to which way is best (if there even is a “best” way). My usual workflow has used the tone equalizer presets as starting points, usually either contrast tone curve: soft, contrast tone curve: medium, or contrast tone curve: strong, adjusting the curve as necessary from there.
They have given me good results, but now as I get more used to the filmic rgb module, I have the ability to adjust contrast there as well, under the look tab. I have the feeling that these two contrast adjustments are fighting each other, but it’s not clear to me which to use and which to leave alone. I seem to recall something in the manual saying that more adjustments should be done in the pipeline before filmic rgb is applied, which would suggest using the tone equalizer. But the contrast curve in filmic RGB seems a little more intuitive to me.
Hi Dave,
I personally don’t use tone equalizer to adjust contrast. Filmic, Sigmoid, Color Balance RGB are the main modules I would use for contrast. I also often apply the local contrast module.
I mostly use Local Contrast, and sometimes I use ColorBalanceRGB. And I also have confusion about whether the two “are fighting each other” if I happen to use both.
Contrast is really just about making bright parts brighter and dark parts darker… you can do it globally or target it… I’m not sure I understand “fighting one another” I always associate that with one thing undoing another … I guess if you think using more than one tool will cause you to push and pull the tone around?? Boris often also uses brilliance for perceptual contrast… AP suggested not to use the contrast in CB module but if you set the mask options in the mask tab I find it can introduce a nice controlled contrast bump. I will use that and I have quite a few presets for local contrast. I like the look dehaze provides some times. I often blend that in lightness when I don’t want the color change. You can do some nice local changes with the tone eq as well… depending on how picky and targeted you want the contrast each image could call for a range of adjustments so I don’t think there is any one way… Multiply and subtract blend modes can also be used to enhance the element of contrast…
There’s no ‚best way‘ - in that case you‘d have just one module in darktable for that since darktable tries to provide the best tools
Filmicrgb as sigmoid as basecurve is a tonemapper applying a curve at the end of the scene referred pipe (and in scene referred fundamentalistic theory there’s no need for further display referred stuff )
The applied curve affects the contrast so you can control it - but in a limited way: just the steepness of the linear part of the curve and the width and position of it. So it’s fine for an general overall tweak of contrast.
If you need to control contrast in the image, you better do it with toneequalizer or colorbalancergb. Especially colorbalancergb is useful to also take color contrast into account.
For local contrast there are further tools: diffuse/sharpen (not intuitive since you didn’t had a chance to learn it elsewhere before ) or contrast equalizer for a wavelet based contrast
I mostly use the tone equalizer, since it gives amazing control (once you’ve set the mask the way you want it), but I would also not dismiss the rgb curve and tone curve modules. I find those modules very useful if you want to make artistic contrast adjustments. I also like rgb curves for colour grading - a “legacy habit” I ported from my photoshop days.
My personal approach is to use Sigmoid to add contrast, and Tone eq to reduce it (usually starting with a compress shadows highlights preset).
Not sure that makes sense now I’ve written it down…
Thanks for all the great comments. It’s been interesting to see all the different approaches that people use. For myself, I think I’ll probably continue using the tone equalizer for the initial contrast setting, and then adjust from there with filmic rgb, and possibly color balance rgb. (I also very often use local contrast, but left that out of the discussion since it happens post-filmic rgb.)
At one time it came before…I think setting the module order to legacy will leave it in front of flimic… I also recall people discussing this position for some certain application way back when… I leave it where it is now but you can get quite a wide range of effects esp also using bilateral mode…
If you use filmic/sigmoid to change the contrast, you keep the dynamic range constant. That means that when you increase the mid-tone contrast, you lower the contrast in shadows and highlights (fixed range of tones).
Otoh, if you use the tone equaliser to increase overall contrast, you increase the dynamic range, which may push tones out of the displayable range. Of course, you can use tone equaliser to increase contrast in part of the tonal range, but then you will lower the contrast in the rest of the image.
Wrt. the ‘local contrast’ module: I prefer ‘diffuse or sharpen’, as I found ‘local contrast’ increasing the dynamic range (which I had carefully set with filmic before adding the local contrast…).
Oh, thanks for that tip. I’ve never done anything with diffuse or sharpen, but I just spent a few minutes playing around with it and it definitely looks like something I’ll spend more time investigating. I can’t say I understand what almost any of the sliders do, but in my brief experiments with it I like what I see from some of the presets.
I use “diffuse or sharpen” regularly, but so far always through presets with perhaps a modification of the number of iterations. But e.g. the sharpening presets can look ugly with too many iterations! And of course more iterations == slower.
I find it very useful, if you like more subdued effects
Haha, welcome to the very large club! I spent a long time trying to learn how to use diffuse and sharpen from scratch, and although I’m much better with it now, I still can’t say I really know exactly what to do for any given situation. One of the main problems is that there are just so many sliders, which exponentially increases the combinations possible. I wonder how many people have actually mastered this module…
It’s powerful but sticking to the presets and tweaking from there is probably how most people use it.
