Re: curves and gum and Christopher James book

[Kees Brandenburg <ctb@zeelandnet.nl>]

Hello Yves,

The only thing we want with printed negatives is to make them 'behave'  
in such a way that the image tones in the final print are exactly as  
the image tones onscreen. This is the same as in the wet darkroom  
where contrast and density are carefully controlled to get a negative  
that is capable to print maximum black and pure white and translates  
image tones in a way that fits your printing technique.
In making digital negatives there are several ways to arrive (in the  
print) at what you see onscreen. We discussed them at lenght and many  
excellent methods are refined every day and available on the web. All   
digital negative approaches are translating image tones to negative UV  
density to get final printtones that correspond with the onscreen  
image. They do it in different ways though: some use color to block UV  
and some control inkdensity or combinations of both. Each density in  
the file is then translated, linearized, by a curve, to  control UV  
density and behaviour in the negative.

This curving approach differs from a printing aproach with icc  
profiles. If you map onscreen tones to printtones, as we do for our  
own processes, equipment and workflow, there's no big need for a  
simulation onscreen. As you look at Sandy's prints for example you can  
see he both masters the printing techniques he uses as the translation  
from his onscreen image tones to print tones. I'm shure his onscreen  
image looks perfect too.

Saying, if I understand you right, that the onscreen image does not  
look nice with the correction curve applied, or with some kind of  
printsimulation curve as you suggest, makes absolutely no sense. A  
correction curve is an intermediate step to get a good negative.  
What's wrong with that. It's a minor step compared to the long way we  
go to get an alt print. If you care to look into the QuadToneRip  
approach you will also learn that it's possible to put all the curving  
into the RIP (that only costs a 50 dollar shareware fee) and leave  
your onscreen image untouched.

Apart from that it is imaganable to use an icc profiled workflow. But  
to get a good profile for each technique is maybe more complicated  
then the curving approach. A downloaded icc profile of somebody else's  
workflow will never work very well for you because of all the  
'personal variables'. The nice thing of doing it yourself 'the hard  
way' is that you understand the relation between digital image tones,  
inks and substrates and the caracteristiques of your lightsensitive  
material. And all that at very low cost.


kees


On 11 mrt 2008, at 07:59, Yves Gauvreau wrote:

> Michael,
>
> Lets say we want to simulate what a print of some image would look  
> like on screen. A print that would have been made with a strait PDN  
> or RNP negative of course. One simplistic way to do this would be to  
> use a strait line "curve" where you change point(0,0) to say  
> point(0,15) and point(255,255) to say point(255,233). Now, I would  
> believe not many of you would like this new on screen image.
>
> The question that come to my mind is why a print that transformes  
> your original in a very similar fashion as above become something  
> that everyone seems happy about? Do you all accept these limitations  
> as part of doing alt-prints?
>
> Regards,
> Yves