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List:       kde-kimageshop
Subject:    Re: Wanted: channel remapping with implicit colorspace conversion
From:       Cyrille Berger <cberger () cberger ! net>
Date:       2008-09-17 20:39:50
Message-ID: 200809172239.51040.cberger () cberger ! net
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On Wednesday 17 September 2008, Matthew Woehlke wrote:
> But I *do* want to have it where it contains the full de-bayer precision
> with the white balance / exposure / curves / everything as filter
> layers. It sounds like that won't be a problem, though :-).
That's what I really want too :)

> >> Other than being measured in E.V., is exposure really substantially
> >> different from brightness/contrast? It seems that Exposure+Contrast (as
> >> done by rawstudio) is just a simple 'Ax + B' mapping of the input data.
> >> So as long as you translate to a colorspace that doesn't lose precision
> >> too early in the pipe (I'm thinking, probably fp32), you should be able
> >> to emulate everything with curve mapping, no?
> >
> > Yup. If you can make a curve that simulate a multiplication ;)
>
> Um...? If I apply the brightness filter "2x + 0" (that performs a linear
> mapping 0->0, 128->255), isn't that simply a straight-line curve filter
> with those endpoints?
>
> What am I missing?
>
> A curve is merely an arbitrary function represented as a traditional
> graph (and usually specified as an interpolated curve). Therefore, any
> filter whose output is exactly one pixel for exactly one input pixel,
> with no other (non-constant) inputs, can be represented as a curve. It
> may have an inordinate number of points, but...

Yes but most curve widget don't allow to all kind of curves (unless you add a 
lot of control points). For instance, I have never been able to make a 
correct gamma correction with a curve widget. But yes indeed multiplication 
is easily done since usually with only two points you get a line.

-- 
Cyrille Berger
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