monotonic spline interpolations in Darktable

Software darktable
41

No. You can conceptualize a cubic B-spline as

  1. values and derivatives at nodes (+ end conditions), which can be
  2. mapped to polynomials.

The interpolations I am considering adjust the derivatives, inserting a step between 1. and 2.

(There are other schemes, eg Schumacher, that insert extra nodes to maintain monotonicity; I am not considering these).

42

Maybe just steal the code for curves from RT/ART?

I moved one node up and got these results:

ART curve:

image
image520Ɨ625 16.3 KB

DT curve:

image
image511Ɨ815 75.3 KB

43

stealing the curve is just possible if the underlying math dealing with color information is the same.
There hasnā€™t been a convincing solution to deal with the curve in a different way than itā€™s done by darktable yet - if it wouldā€™ve been that simple, Iā€™m pretty sure we had already seen a RFC pull request ā€¦