On Jan 5, 2018, at 5:21 PM, Florian Höch <lists+colorsync-users@hoech.org> wrote:
Hi,
Am 05.01.2018 um 18:11 schrieb forums@walkerblackwell.com:
A typical print RGB ICC will create contrast curves to match print output to a monitor. When printing on low dMax papers (matte) this contrast curve is higher than on high dMax papers (glossy).
Not sure if there is such a thing as a "typical print ICC" (profile?).
The gamut mapping in the perceptual table of print profiles is vendor-specific. It may do a viewing condition adjustment from (assumed or defined) source to destination, or some other transformation, or it may be purely colorimetric with compression (and expansion) of the lightness axis (also known as black point compensation), or something in-between, something entirely different, ... - vendors are free to do whatever.
That’s been my problem/observation over the years even though I rely on these vendor specific tweaks every day to keep things simple between different papers types, printers, work spaces, viewing spaces, etc. What I’m trying to do is something entirely different and not industry sanctioned exactly. I guess I’m trying to do a viewing condition "chiropractor adjustment": to create a system for predictably printing values that are aligned from dark to light (as measured in L* D50 from a spectro) and have that calibration happen only in the output ICC while leaving the source image/colorspace alone and without funky curves anywhere else but inside of the ICC . . .
The colorimetric table just maps input (PCS) color to output (device, i.e. RGB or CMYK) values, clipping any out-of-gamut colors (but there are different ways to do this, too).
hmm. I will look into this. Thank you.
My question is this: is there any ICC system out there that you know of that does not create this contrast curve?
So you want colorimetric then (probably with BPC so lightness axis is not subject to clipping).
ok. I will investigate. Thank you.
Let’s say we have 18 equidistant values (actual patches in a target) from 0-255 in Photoshop. These would be
[...]
Let’e say our dMax is L* 14.45 on Matte Paper and our dMin (paper white) is L* 96.5
So, Photoshop value of 0 of would be L* of 14.45 and Photoshop value of 255 would be L* of 96.5
What I’m talking about is simple. Is there a consistent way to calibrate with an ICC such that numbers above print like this when measured with a spectro (approximately as the real values have been rounded to 2 decimals):
Sure. The spacing (and meaning) of the values in the source (image) file as outlined mandates the use of a L*-based source profile. It's not related to the output (print) profile at all.
But if you were to just assign this source profile to a source (image) file that originally used an encoding with another tone curve characteristic, think again. I.e., wether the values are spaced according to L* is independent of the encoding. It's perfectly possible to have (e.g.) a gamma 2.2 source file with contrast steps being visually equidistant according to L*, you'd just have to space the values accordingly in the file:
L* (0..100) -> R=G=B gamma 2.2 (0..255) --------------------------------------- 5 -> 24.03 10 -> 33.18 15 -> 42.17 20 -> 51.71 ... etc.
If you were to decode these values according to L*, the contrast steps would no longer be equidistant. You'd have to decode with gamma 2.2 to arrive (again) at the equidistant L* steps.
So, all in all, your question seems to be more related to how your source (image) files are created, than the profile(s) used.
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