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Re: [QuadtoneRIP] Re: New to Linearize Piezo K7 inks with Eye One 2 X-Rite software

2015-02-09 by Ernst Dinkla

There is a distinction between linear in density (measurements) and what the eye sees as linear so a perceptual linearity (Luminosity of Lab). About ten years ago when the linearisation/profiling for QTR was discussed we suggested a perceptual approach and by that the ICC profiling basics are the easiest way to get there.

Tweaking that approach may be necessary too as Black Point Compression on shorter dynamic ranges of prints is not ideal, whether RC + BPC or Perceptual rendering is used. There have been discussions on that subject too I think. Different color engines in applications show some differences in those renderings too.

On the sideline here but were Paul Roark's, Eric Chan's profiles not more tweaked for similar reasons?

Before that approach there were some generic QTR profiles for resp matte and gloss paper and Roy then also created an alternative space for Gamma 2.2 to assign to B&W images, it was called Gray-Lab.icc. The RGB version RGB-Lab.icc. The Read Me file says:

>>Gray Working Space

The first is gray-lab.icc which is an abstract gray space to be used as your gray working space in Photoshop. It spaces the grayscale values linearly with respect Lab or Luminosity. As opposed to a Lab space which is for color this space is a single channel gray space with the same spacing as Lab. Compared to Gray Gamma 2.2 it displays slightly darker through the mid values but opens up the deep shadows from K = 90 to 100%.<<

So neither linear or Gamma 2.2 but closer to the last.

What should be the ideal workflow today is harder to say. Roy may shed a light on that.


Met vriendelijke groet, Ernst

http://www.pigment-print.com/spectralplots/spectrumviz_1.htm

December 2014 update, 700+ inkjet media white spectral plots





On Mon, Feb 9, 2015 at 3:41 AM, brian_downunda@... [QuadtoneRIP] <QuadtoneRIP@yahoogroups.com> wrote:

I understand that. I understand it only too well. Indeed that was precisely the point of my post - that they *are* two entirely different philosophies about how to print monochrome using QTR.


Despite this, Roy's post suggested that you could mix these two different approaches, and use the ICC approach to linearise the Cone curves. As I demonstrated, you can't, or at least not in the way that he suggested and still work within the Cone approach. It's not that simple. I confess that I thought it was, but it tried it and see that it's not.

So two questions remain. 1. is there a way to linearise the Cone curves, in a way that Jon Cone would think is linear? Michael seems to have an approach. If you look at the second image I posted, you see that after conversion to the ICC, the luminosity values lie on a smooth curve. In theory it should be possible to apply a Photoshop curve which is roughly the inverse of the curve you see in that image. That's what I'm trying. Partial success so far.

2. I'd really like to get a better understanding of how two such eminent people in the monochrome world use the word "linear" to mean something so different. I understand what Jon Cone means - you see it in the linearisation plots. What does Roy mean?

Brian

---In QuadtoneRIP@yahoogroups.com, wrote :

Jon's curves assume Gray Gamma 2.2 input files. Roy9;s curves assume linear input files. Two fundamentally different approaches using the same tool (Quad Tone RIP).

Terry.


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