[Gegl-developer] Curve - First iteration

[Mark Probst]

On 5/17/07, Øyvind Kolås <pippin at gimp.org> wrote:
> I think we want a bit more functionality similar to the one already
> existing in GIMP as well,
> for instance making sure the values always add up to 1.0 to maintain
> the range in the image

I don't think that's a good idea.  First of all, ensuring that they
add up to 1.0 does not guarantee that the mono range stays withing
0.0-1.0 (if the red weight is 2.0 and green and blue are -0.5, then
pure red will get a value of 2.0, while pure green and pure blue will
get values of -0.5).  Second, sometimes values which don't add up to
1.0 give useful ranges anyway.  In practice you have to make such
adjustments by looking at the resulting histogram.  And limiting the
weights to non-negative numbers won't do either.  Here's an example of
a photo that I made using negative weights:

  http://www.flickr.com/photos/schani/336705437/

A question, though: Does an operation have to make sure that the
values it produces are within the 0.0-1.0 range?

What other requirements would there be for making it a "proper" operation?

> Speaking of color to gray scale, be sure to test the c2g operation
> also in the workshop.

I will.

bye
Mark

-- 
Mark Probst
  http://www.complang.tuwien.ac.at/schani/
  http://www.flickr.com/photos/schani/
  http://schani.wordpress.com/