Photoshop curve with more than 16 points?

[J Isner]

I have a strange application that needs an accurate adjustment curve with more than 16 points (probably more like 40). I'm wondering if there's a workaround for the 16 point limit in the Photoshop Curves adjustment.  I know that Gradient Maps can have many more stops (probably up to 100), but the stops must be placed at whole percentage values.  This makes Gradient Maps inherently less precise than Curves entered with Light (0-255) display option.  Just wondering.

[Semaphoric]

Maybe you could do something using the Pencil option in the Curves dialog. Davide Barranca does this in his Parametric Curves plugin.

While using the Pencil, each Input value has its own Output value, like an 256 wide array, until you click on the Curve option, which smooths it (sometimes a little agressively, it seems).

[J Isner]

Thank you.  That's a very interesting idea.  I will look into it.

[Chuck Uebele]

Yea, using scripts, you can create some unique curves, like this circular one:

 

[J Isner]

I think I found an answer.  A 1D LUT with 256 rows from (0,0,0) to (1,1,1) is equivalent to a Photoshop curve from (0,0,0) to (255,255,255).  That is, it is a linear curve that has no effect when applied as an adjustment layer.  But if you change the values in any row of the LUT to some other value, it makes the curve shift up or down at that point. It's like using the pencil at a given input value to change the output value.  Extend the idea to all 256 points and you have the equivalent of a 256 point generalized curve.  Like the one below!