I'm sure this is probably a Photoshop Color Management 101 question, but since my last basic
question resulted in me discovering that my Canon glossy paper profiles were broken, I figured it can't hurt to make sure I properly understand a few things regarding Absolute Colorimetric rendering intents.
Quick context for the questions: My goal has been to duplicate the appearance of some old photos as close to the original as possible. I think I made the mistake of asking a too-detailed question about
color casts in my scans instead of breaking it down into core components first and checking my understanding of each phase. My follow-up question about the broken rendering intents of my Canon paper profiles helped me realize that printing my scans using a functioning Absolute rendering intent improved my results by emulating the paper white of the source photos onto the paper that I have at my disposal.
As a test, I'm currently working with
a simulated ColorChecker image from BabelColor, since its Lab values match the reference file of the physical ColorChecker Mini that I have and I can tell what they're supposed to be.
In Photoshop under Edit > Color SettingsDoes this just control how the current image profile is translated into my display profile and what the Info panel numbers represent? The default is Relative, but when doing reproduction-style work, is it best to leave this in Absolute Colorimetric to make it easier to check that profiles are working properly?
Using Edit > Convert to Profile vs Soft ProofingIf I take this ColorChecker image and convert from Lab to sRGB using Absolute Colorimetric for example, most of the patches stay the same since they're almost all within the sRGB gamut, the cyan shifts a bit. What I'm confused by is that if I convert from Lab to most of my paper profiles using Absolute Colorimetric, is that the patches will obviously shift. For example: If I choose a semi-gloss paper, the L of the white patch goes down, but the RGB values go up and the image gets brighter on the screen as a result. It seems counter-inuitive. Does this have something to do with how it preserves the white point of the source relative to the destination profile? (I can include photos if my description is gibberish.)
If I take the ColorChecker and proof it using Absolute Intent, unlike Converting the Lab values all stay the same but the image on the screen will clearly change depending on my settings for simulating paper color, etc. Is the proof just trying to emulate what the actual Lab values will look like when printed vs. the Convert reflecting the actual changes that must take place to preserve the appearance? I just want to be clear on the distinction going forward.
Finally… evaluating the printIf I print the ColorChecker image using Absolute Colorimetric, I think I read in a few posts that it's possible to sample the output using a spectrophotometer and compare to the original. Is that correct? If so, what should the numbers be a match to – the reference Lab values, or the values after converting to the paper profile using an Absolute intent? Or can I really only just view it by eye to evaluate?
The sample I printed yesterday on my Pro-10 (from Windows with a working paper profile) using Absolute Colorimetric looks nice and vibrant with a slightly off-white white patch and the greys appear pretty neutral, though my glossy print vs the physical ColorChecker obviously reflect light differently.
For the heck of it, I did use
spotread from ArgyllCMS to measure my printed patches…
Printed target using Absolute Colorimetric:Canon glossy paper white: 94.055, -0.611, -2.047
ColorChecker white: 92.887, -1.425, 3.816
ColorChecker grey (under the yellow): 47.370, -0.039, -0.405
ColorChecker black: 16.089, 0.091, -1.236
Target Reference Lab values:White: 95.19, -1.030, 2.930
Grey: 50.76, -0.116, 0.141
Black: 20.64, 0.070, -0.460
Target converted to the glossy paper profile using Absolute Colorimetric:White: 93.31, -1.147, 2.273
Grey: 51.04, 0.164, -0.444
Black: 20.45, -0.077, -1.827
Thanks for any feedback!
*** 5/12/2018 - Edited the title