Re: curves and gum and Christopher James book
Kees, I agree with you on this, "in such a way that the image tones in the final print are exactly as the image tones onscreen", it is the goal of every one. Unfortunatly, it is not what happens with real prints. Remember the part where you basically stretch the scan values of your digital step wedge test to bring them in the same range as the screen values? Whichever way you look at it, either stretching the scan or compressing the screen image are equivalent transforms and that changes the relationship between your original values. Say I ask you what would happen if you do the following experiment, place a blank piece of your transparent material (no ink) and a piece of UV opaque marerial beside it. You expose and process this test as usual, now if you scan this without any adustments and both the darkest black doesn't result in a 0 value and the whitest white doesn't result in a 255 value, that means you can't print any original values under and above those 2 limits for one and worst you have lost the relationship between values you work so hard to get. Basically the transformation that happens is equivalent to the crude experiment I suggested below. That may result in a print you like and I can't argue with that, it's a question of personal taste but for myself using a method of making a digital negative that is bound from the start to modify the relationship of my work, will simply wont cut it for me. Regards, Yves ----- Original Message ----- From: "Kees Brandenburg" <ctb@zeelandnet.nl> To: <alt-photo-process-l@usask.ca> Sent: Tuesday, March 11, 2008 5:54 AM Subject: Re: curves and gum and Christopher James book > 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 > > >
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