True, while none of us understand precisely how Jon Cone creates K7 curves, several of us claim to have ways of hacking or tweaking the .quad files. But no-one has said precisely how they do it. Michael King has never published his spreadsheets. Richard Boutwell is writing a book, although it's not clear to me whether he has a way to re-linearise a K7 curve from IJM, or is creating them himself from scratch using the QTR curve creation tools.
For my part, I've got a spreadsheet or two, but I've been hesitant to document this because I don't fully understand the maths. There's no "incredible complex equation", although it's a little messy. I can calculate ideal and actual densities for a K7 curve, but I can't work out how to translate these into modified values in the .quad file. Well I can, but my current approach doesn't linearise the .quad file sufficiently. I'm missing something. One day I might ask Roy about the bits I don't understand. So I took a different route.
I am setting up a B&W blog (isn't everybody?) where I will probably document this. But I am time-poor at present and will be offline for much of the next few months. So here is a sketch outline of how I do it at present.
1. I create a dummy curve in QTR that uses only one ink - Shade 1, and let it range from 0 to 90%. I use an existing curve as the base, but strip out all the linearisation etc data. I instruct QTR to generate a .quad file. I put this to one side as a reference point for step 3.
2. I then take the linearisation data that I get from dropping the measurements of my 21x4 chart (I actually use a 51x3 chart) onto QTR-Linearize-Data, and input this data into my dummy curve. I regenerate the .quad file.
3. So now I have two .quads - one generated without the linearisation data and one with. In a spreadsheet I take the ratio of these two columns of numbers for shade 1, and scale the values of each of the seven shades in the real K7 .quad file by this set of 256 ratios. Setting up a spreadsheet to do this is a little tedious, but once you've done it, you can reuse it. The relinearised .quad isn't quite as straight as a $99 curve from IJM, but by golly it's close. Certainly close enough IMHO.
I'd like to be able to do this entirely in a spreadsheet using the measurements of the 21x4, i.e. without resorting to QTR and dummy curves. I've come close, but there's something small I don't understand. Perhaps I will ask Roy when I have more time. Anyway, you can either try to understand and replicate what I've done, or wait a couple of months until I blog all this, with the necessary files.
No dragons, just the Triantiwontigongolope.
"When first you come upon it, it will give you quite a scare, But when you look for it again, you find it isn't there."
---In QuadtoneRIP@..., <ciprian333@...> wrote :
Jon Cone places a premium on preserving shadow detail and opening the
shadows, and tells you *never* to convert to the ICC, only
to use it for soft-proofing. But if you follow this workflow, you've got no (easy)
way to re-linearise the K7 curve. You've got to pay $99. Or develop a
spreadsheet to hack the .quad file.
<sigh> And this is the part where all the stories end-up with a big "here be dragons!" sign.
Brian, is there some reference some theoretical framework about the math involved, about the algorithm, something that would point out to the steps needed to linearize a K7 ink set? In other words, why is that everyone seems to be so afraid of the math involved in the linearization process? What's the catch? Are we talking incredible complex equation systems or something like that?