Re: curves and gum and Christopher James book

[Kees Brandenburg <ctb@zeelandnet.nl>]

Hello Henry,

A correction curve that is meant to be used on a positive image before  
inverting to a negative should not be confused with a curve that has  
to be applied to an allready inverted image. There are two 'schools'  
of curving for digital negatives. It's a bit like driving left or ride  
side of the road. In both cases you will arrive from A to B but you  
should never mix the methods.

Anyway, sometimes it comes handy to change a 'before inverting' curve  
into an 'after inverting' curve. For example when you want to build  
your curve into a QuadTone Rip profile.

This can be done with the Curve Merging technique described here: http://polychrome.nl/weblog/curve-merging
Actually you will not merge two curves here but you 'wrap' a curve  
layer with your curve loaded between two invert layers. Then you have  
to flatten this package and save the .raw file as a .amp curve. When  
you load that curve you can change it to a regular .acv by clicking on  
the pencil symbol in the curves palette. When I find some time this  
week I'll write an article about this on my site.

Kees


On 10 mrt 2008, at 20:09, Henry Rattle wrote:

> Michael – you are right, of course. But my question was more about –  
> shouldn’t a curve that you apply to a positive, curve in the  
> opposite direction from one you apply to a negative?
>
> David’s curve, like mine, has the shadows in the bottom left corner.
>
> H.
>
>
> On 10/3/08 18:44, "Michael Koch-Schulte" <michael@mondotrasho.ca>  
> wrote:
>
> > Henry, it all depends how the curve data was gathered in the first  
> > place. Neither is right or wrong it's more a matter of workflow. I  
> > choose to apply my curves to the positive because I'm taking my  
> > readings from a developed positive. I also like to work in PS with  
> > the curve putting my highlights in the bottom left corner using the  
> > graphic scale of 0-100 rather than the binary scale of 0-255. The  
> > important thing is that you apply the curve to the image at the  
> > correct stage of the procedure. Dan Burkholder started doing it  
> > this, I also do it this way. It intuitive for me. Others apply the  
> > curve to the negative.
> > ~m
> >
> >
> > On Mon, Mar 10, 2008 at 6:53 AM, Henry Rattle <henry.rattle@ntlworld.com 
> > > wrote:
> > > However one thing puzzles me - there's a note alongside the curve  
> > > which says
> > > "Note from David: The curve is applied before inversion to a  
> > > negative and
> > > the image should be RGB."
> > >
> > >
> > > Henry