Should the mask adjustments in tone equalizer be improved

[g-man]

I think looking at the image is more important than how a curve looks.

[Terry (Terry Pinfold)]

I totally agree. That is why I love to hover the mouse over the picture and scroll wheel, but sometimes I have then gone to the simple sliders to ensure smooth transitions …but now I wonder if I just should have done that using the nodes on the graph. I mistakenly believed the slider only affected that node, but I was wrong. This mistake came about because when the simple sliders are accessed the graph and nodes of the advanced tab are not visible, so the user is just guessing what is happening to the graphs shape.

[kofa (István Kovács)]

There was a discussion, I think started by @Tamas_Papp , about fixing curves so they avoid oscillations (e.g. in the color equalizer), but then it just dried up. I think it was a good idea.

Yes, I found it:

monotonic spline interpolations in Darktable

A lot of great modules in Darktable (tone equalizer, contrast equalizer, color equalizer, did I miss something?) are parametrized by a continuous (possibly periodic) function, specified by a few control points, which are then interpolated. The problem is that the interpolation does not preserve monotonicity. This is familiar to all users, but in case someone has not encountered it, here is an example: [screenshot_2024-08-07-093005] I wonder if it would make sense to replace the interpolation …

[g-man]

@kofa

about fixing curves so they avoid oscillations

Are the oscillations in the data and how the image transitions are handled or they are just an effect of how gtk draws the line in the graph without any impact?

[europlatus]

@Terry

Hmm…I stand corrected. The simple sliders don’t function how I expected. Here I have only adjusted the -4 slider.

Yes, this is a good example of what I was saying. I think what many people want is to adjust a slider and it only affect that EV value, or at least just a stop or two either side of it.

The Tone EQ module sometimes requires dozens of clicks, back and forth between tabs and little adjustments of nodes, to get the look you want. And this is the source of the frustration. One issue is because of the tabbed interface, and the other is because of the way the curve works.

Thinking more about this:

@Terry

It would be great to have an automatic calculation of the settings so that the mask covers the full histogram.

I was wondering if something like this would work:

• Use a picker to draw a rectangle around part of the image. This could be the whole image (default) or just an area, such as the shadows or highlights.
• Then the tones in this picked area are automatically mapped to span the full range of nodes (darkest part furthest left, brightest part furthest right).
• Then you can adjust the nodes to add or decrease contrast as desired.

I have no idea if this is feasible, but to me it seems like quite a streamlined workflow that would avoid messing around with the mask exposure and contrast sliders too much. And since the tonal range is spread out over all nodes of the graph, it would also avoid needing to have steep changes between nodes.

[rvietor]

@g-man

Are the oscillations in the data and how the image transitions are handled or they are just an effect of how gtk draws the line in the graph without any impact?

They are not a drawing artficact.

Darktable uses a spline fitted to the points in the graph. The nature of that spline creates those overshoots if only one point is moved. This system is used in several modules. (see the thread linked by @kofa for more details)