Wanted: channel remapping with implicit colorspace conversion

[Cyrille Berger]

On Monday 15 September 2008, Matthew Woehlke wrote:
> (Please let me know if there's a particular spot on the wiki you'd like
> me to add this to.)
>
> IIRC, a while back I'd talked about a way to transfer a color channel to
> an alpha channel via a node (i.e. such that it dynamically updates).

A filter could do that, the alpha channel (and obviously other the other 
channels) are available when filtering. That's basically what the Color To 
Alpha filter does.

> I'd 
> like to restate a desire for this, and also a way to create a
> single-channel layer from another layer via colorspace conversion (i.e.
> extract the effective "K" of CMYK from an RGB layer, etc.).
A filter sounds also the correct solution.

> As I recall this was in connection with generator layers (which possibly
> produce exactly a float-16/32 gray channel) to be able to get alpha
> layers out of them, but I realized they are useful for HDR photography
> workflow.

Sorry I don't understand what you mean by that.

> Specifically, I want to be able to do this:
>
> -Start with two exposures of a raw*, 'e1' and 'e2'.
For 2.0 (at least), the raw would have to be converted to one of the HDR float 
color space.
> - Copy the luma channel (HCY, or maybe LAB, color space) from e2 to its
> own node.
> - Create an alpha mask from that (bonus points for combining this with
> the previous step).
> - Apply filter layers (blur, unsharp mask, and curves being the likely
> suspects, but any filters should be possible) to the mask.
> - Combine the mask with a second mask layer which is hand-painted.
> - Use the resulting mask to blend e2 onto e1.
>
> (* Currently I'd be doing this via rawstudio and 16-bit TIF export.
> Bonus points if Krita can do everything rawstudio can... which I *think*
> it can, except it seems raw import wasn't stable last I tried,
/me looks around for the bugs reports ;) I only tried with nef and it works 
fine for me.

> and possibly filter layers are still a bit flaky.
Yup indeed.

> Quadruple bonus points if it can import the .xml's from rawstudio :-D.)
I fear we are going to fail on that ;) (unless someone offers a patch ;) )

-- 
Cyrille Berger