Recently I have started to review and compare the way the curves tool works in various packages, particularly in Photoshop, GIMP and my own PhotoFlow.
I personally think that there should be some harmonisation in the way the curve points are interpolated by the different softwares, so that for example a sentence like “pull the mid point 1/4 upwards” would produce the same result independently of the software being used.
Currently this seems not to be the case. Here are three examples of a curve obtained by inserting a point at the (57/255, 101/255) coordinate:
Photoshop (taken from How to use curves | Pavel Kosenko):
As one can see, the interpolations in the different softwares do not really match.
The interpolation done by PS and PhF seem to be quite similar, while the GIMP curve is much more straight, with a stronger curvature around the control point…
I need to do some more experimenting, but this should already give the general idea of what I am talking about.
I guess it will be very difficult to change the way the GIMP curves are defined, on the other hand I believe that a more standard curves behaviour would simplify the exchange of tutorials from one software to the other…
What do you think?