There is no white and there is no black in a scene-referred pipeline. That kind of thinking applies only to a printing medium. In the pipeline, you have a range of light energies and no prior information on them, except how they look once they get projected onto your screen, which is unknown from the pixel algorithm. All we can do is to apply a gain (exposure compensation) and a fulcrumed gain (contrast compensation).
Right, my bad. The names were poorly chosen, since we are in scene referred. I meant “white” as in the brightest value in the mask, and “black” as the lowest value in the mask. Since the guided filter reduces contrast, they are both probably going to be shown as shades of grey (unless the exposure is way out of what my screen can show and filmic is not activated, right?)
The question is: can we divide those 2.5EV equally into 9 nodes and have the module work properly?
No. The radial-basis interpolation has 8 hard-set values for performance. Then, if we do that, copy-pasting presets becomes impossible.
Bummer…If each of those hard-set nodes need to be 1EV apart instead of say 0.1EV or whatever the case may require, then my suggestion wouldn’t work.
What I don’t understand is why this would break copy-pasting presets. Leaving the hard set values aside for a moment, if you have 9 nodes spread out evenly throughout a histogram, as long as the brightest node matches the brightest level in the histogram, and the darkest node, the darkest, wouldn’t the effect translate perfectly between images? For example: if I increase the exposure of the third brightest node by 0.5EV, wouldn’t the effect be the same on the final image regardless of the dynamic range of the generated mask, assuming luminance estimator, preserve details, filter diffusion, smoothing diameter and edges refinement/feathering remain constant? What would change the final result would be if you alter any of those last five parameters, right?
Finally, that requires running several pipelines computations (one for detection, one for actual processing), which is not allowed by the current pipeline design. That’s why any detection thing (spot WB, vertical/horizontal lines, etc.) needs a push on a button.
I don’t mind pushing a button or moving a slider, or a couple of sliders. My issue with the exposure/contrast compensation, is that it is a bit of a guessing game. You press the button, and each time the result changes slightly, often not spreading your histogram very well across the nodes, so you have to go back and forth between tabs.
If exposure/contrast compensation are a bit fiddly to use, have the potential to screw up the guided filter at high values, and their goal is to spread the mask across the 9 nodes, wouldn’t it be easier (in an ideal scenario) to tell the module: these are the settings for the guided filter mask, dynamic range will be reduced accordingly, but this are the brightest and darkest levels in the mask, so please divide it evenly into 9 nodes.
In any case, as a principle, I disregard anything that begins with “simplify”. What we are doing is not simple, the GUI should acknowledge that. Also, if it was simple, it would have been done already. I’m not known to be lazy and to pass on good opportunities to make things faster and easier, but sometimes you hit a good old technical wall that has no solution on paper. Like, in this case, predict how much contrast will be lost by applying a variance-thresholded edge-avoiding blur.
I am sorry if I gave you the wrong impression. It’s hard to communicate the right tone through writing and english is not my first language. I chose this thread, since it had semi recent activity, and a lot of comments, but I didn’t pick the title. I know you are not doing simple stuff by any means, are lazy or don’t want to improve the tools you cleverly designed. My comments, opinions and mockups come from a place of admiration and respect for your work on darktable in the hopes that they might help any of you improve the tools we have. If this particular case can’t really be improved, I will still use the module. It’s not the end of the world, and what it allows us to do makes up for going back and forth between tabs and sliders.
Cheers!
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