johannes hanika <hanatos@...> writes:

> 
> hi,
> On Tue, Jan 6, 2015 at 8:42 PM, Mueen Nawaz <mailinglists <at> nawaz.org>
wrote:Hi,
> Has anyone considered adding luminosity masks
> 
> oh i'm glad you asked.. there might be a blog post coming up exactly about
that (translating this word into what it's called in darktable, and we've
had this feature for quite some time now. it's called parametric blending).

I'm aware of parametric masking (which I assume is the same as parametric
blending) - I mentioned it in my post. 

I was going to express skepticism that one could achieve this result with
parametric masks, but now that I read Pat David's article in more detail, I
think you may actually be correct.

The L mask is just a luminosity layer. So with the parametric mask, if I
keep the bottom triangles on the input fixed, but move the left upper
triangle all the way to the right, I think I'll get the same effect as his L
mask. 

The D mask is likely the opposite. Instead of moving the left triangle, I
should move the right triangle all the way to the left. 

The M mask is a trickier. In his article, the M mask is the intersection of
L and D. I could simply move the two upper triangles to the center. This
isn't quite what Pat has in his article, as the his M mask has no pixel more
than 50% selected, whereas my approach would have the central tone be fully
selected. I could perhaps drop the opacity to 50%. I'm not sure if this will
exactly get the same as the M mask, but I could play with it.

The remaining layers he had (LL, LLL, DD, DDD, MM, MMM) are not as
straightforward to translate to Darktable. For LL and LLL, I suppose I could
just move the bottom left triangle further to the right to simulate it. The
interpolation in DT is still linear, though - I'm not sure it is in his LL,
LLL. I think once I go home and fiddle more I'll see if the linear vs
nonlinear interpolation makes a significant enough difference. Perhaps it'll
be "good enough" even if we can't exactly duplicate his masks. 

Mueen


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