Hi, Sorry for such a long message, but I think, it's really a tough topic, which is so interlinked that it can't be split into pieces.
Since quite a while I'm trying to get started with the new modules in darktable 3, but without success. The promise of gracefully dealing with high dynamic range scenes, on the other hand, is really seductive. I've watched Aurelien Pierre's videos several times and searched the net for answers, but only got the impression, that most aren't doing so much better than myself. Everything seems to indicate that this can't be learned without a considerable amount of understanding, while all these modules are less artistic than technical, mathematical issues. This, in spite of some obvious efforts to make it 'easy to use' (which actually complicates matters, as it makes it harder to understand the inner workings, or matching concepts about color science, I've already learned in a different context). I think to have understood, that exposure, filmic and tone equalizer are there to map the scene's dynamic into a range of intensities that fits into the dynamic, the internal color space is able to work with. At the beginning I though that 'linear RGB' meant some sort of radiometric proportionality, but reading some Wikipedia articles about ACES tells me that this should all be in the photometric domain. But it is sort of a mixture, at least in my head, as the exposure module comes very early in the pixel pipe, is declared to work with linear RBG but uses EV units, which are a logarithmic concept. I'm using a self made ICC camera profile, which I always thought of dealing with photometric entities. On the other hand, there are many articles pointing out, that a 'gamma transform' is an inheritance of the cathode ray tube monitors, which today isn't really needed anymore and, if used, will be undone before lighting up a LED on a modern monitor. So what is the color space, which the exposure module is working in, actually linear to? Filmic's S-shaped curve reminds terribly of the gamma correction. Aren't photometric entities already adjusted for the behaviour of the human eye and brain? Being a technical/mathematical issue, it must be possible to state a goal which should be achieved with each of these three modules. I believe to have understood, that the black level correction in exposure must be so low as to avoid zero or negative RGB values later, in a more logarithmic domain. So the goal might be just to accept the setting which can be found by clicking on the pipette icon near ''clipping threshold'', no matter how washed out the image might look. If that lowest level of intensities is fixed, any change of exposure in the same module needs to perform some sort of uniform compression or dilation. But the drawings in one of Aurelien Pierre's videos seem to suggest a more linear shift of the scene's dynamic range with regard to the dynamic range of the internal working color space. Where did I miss the turn? At one point, Mr. Aurelien Pierre states, that one can either try to fit the highest intensities into the histogram, or trying to set the mid tones right, even if this makes the highest intensities appear overexposed; it wouldn't matter. At another point he says, that it's the second option which should be chosen, which may be in sync with the fact that in the later versions of filmic:scene, the setting of the middle grey is already only optional, as that should have been done before in the exposure module. For that, I should (mentally) adjust the exposure module, such that a rectangle within the image, enclosing an area which in the scene has about the same brightness as my grey card, yields something close 18.42%. If this was right, I wonder, why the exposure module doesn't have a function similar to the fulcrum pipette in color balance. So, what is the goal I have to look for, such that the following modules allow for a successful adjustment? If the exposure module with regard to some unknown rules is rather off, there is no chance to get the other modules right. I've found out that much. I've found even less clues for the final goal in the filmic rgb module. I think I did understand, that it is the shape of the S-curve, which marks the transition of the linear to a more logarithmic distribution of the intensities. Beyond that, I'm really lost. Where should I start? The module opens with the scene-tab, but the look-tab already has some settings that directly affect the effect of the white and black relative exposures. Both tabs together have 7 parameters. Just trying to guess a combination of them that 'looks good to my eye' is really difficult. As a matter of fact, watching the videos, Aurelien Pierre also switches back and forth many times, the only difference beeing, that he does know exactly what he's doing and being successful, and I don't. So, where do I start, and what should I look out for at each point? Also the tone equalizer seems to be much easier when Aurelien Pierre is using it. In the live video, one of the guests mention that 'the mask interface needs some more love'. I couldn't agree more! I've tried to do something like in the video, but there are so many cases where two areas in the image fall within the same range of EV but should be adjusted differently. Excited by the promise, being able to deal with high dynamic ranges, I shot a bracket of my living room, having weak but direct sunlight caught in the curtains at one side, and a rather dark corridor at the other. A second image was of a building's front. The sunlight came almost straight at 90 degrees from a side, not falling on the building, but there is a mid sized object in front of the building at an angle, picking up a rather harsh light. Nevertheless, besides some tiny spots, the image isn't overexposed on the sensor (as indicated by darktable). I wasn't able to improve any of these to cases. Switching between the original image, each step in the history stack seems to make it worse. I don't want someone fixing these images for me; these are only for learning. I'm asking for explanations that will allow me to fix these and all other images I'm (not yet) planing to shoot. The main question is: what goal do I need to achieve at each point? I'm convinced, that there must be many users of darktable out there, struggling with these new issues. ____________________________________________________________________________ darktable user mailing list to unsubscribe send a mail to [email protected]
