Well, let’s start over again.
It does not matter in absolute figures, I totally agree. It doesn’t matter to me which node to manipulate: 0EV or -2EV, indeed. But! What matters is how many nodes I may really use to distinguish between differently lighted areas (the whole thing is about it, isn’t it?). If it’s only 2 nodes available, the module becomes just an exposure module with unobvious interface. Also, it does matter in terms of relative luminance. If areas with quite different luminance fall into the same EV while evenly lighted area differ 4EV in the mask because one point is on the bottom corner of the picture and another is closer to the center, I’d say it only messes things up, because the results are totally unpredictable in this case.
Not exactly. Again, absolute figures don’t matter, in that sense I completely agree. What I was trying to show you is that relatively lighter areas become darker in the mask and visa versa, as if the conversion function wasn’t monotonic. (And yes, I understand that it may locally be as such, because it’s a smoothed 2D construct while pixel luminance single-dimensioned). I hover over the dark wall, for example, and see -3EV and when hovering over lighter area I see -5EV. Then I get confused and go check with DT picker. It is lighter, indeed. Either this means it works erroneously, or I’m not getting at all what TE is developed for and what it’s supposed to achieve. Do I understand correctly that darker picture areas shall generally get lesser EVs in the mask and visa versa? If so, that’s not what I see…
That’s not what I see. Practically it doesn’t work this way (at least, to me). That’s what I keep telling you. Your mask’s bottom corners are always much darker than its top. Even if the original luminance is spread in another way. So in fact they are based rather on something else (position?) but not “lightness/luminance/intensity”. No matter in this case if it’s scene-referred or display-referred. Conversion from linear space to a logarithmic one doesn’t change the relative lightness that is lighter areas still shall stay lighter, and darker shall stay darker. Which is obviously not the case.
Let’s look at this picture
Which I want to become something like this
That is, I want to emphasize the clouds and rays and lighten up the fort’s wall. But the TE picker shows -3EV on the fort wall and the same -3EV on the far yellow building! However it is lighter, it occupies the same node. Which means that when I start to lighten the fort wall, I’ll lighten all the background embankment and some area on the water – because they are all undistinguishable by the TE module – and that’s not what I want! And visa versa – the evenly lighted water gets about -4EV difference toward the corner. What for? Does it have any practical meaning?
Also, I can’t do anything with the clouds and rays – I simply short of nodes to do that. They’re too close in TE’s opinion. So I failed completely with the TE on this picture, and I had to solve this the old way, namely, to use two curves with masks – one for clouds, another for darker wall.
Look, you don’t owe me anything, and it’s up to you to listen to me or not. It’s FOSS eventually, nobody has obligations to fix issues or whatever, I fully accept that.
But if you so sure the TE works correctly, I offer you a Christmas challenge. Here is my RAW. Make it close to pic #2 in this post, that is, lighten the fort wall without lightening other areas, like distinct buildings, and emphasize the clouds. If you are able to so, I promise I won’t bother you anymore with that. And will consider myself deadly stupid from now on)))
20140522_0041.NEF (23.9 MB)
BTW, I’m not sure if you were able to see this and if this makes any sense or not, but JFYI: https://github.com/darktable-org/darktable/issues/3865#issuecomment-569894506