Greetings and thank you for the warm welcome,
I am sorry if I am dragging you through an area recently covered, If that is the case please refer me to the thread in the archives. I tried to find the reference mentioned above, but without the title it was too difficult.
I began some time ago simply trying to build a zone scale that would correlate Lab values and print densities to enable me to better target files for different devices. Since every devise profile compresses the data differently every print shop sends me back my image with varying amounts of shadow detail distinction. This puzzled me because, though chromatic values , (levels and percentages) are device signals, I thought the lab code defined precise and universal sensitometrical values. I didn�t understand how L* 24 against L* 5 could produce a 1.6 density against 2.1 on one printer and something else on another. Anyway, yes, I was na�ve. In fact I still am to keep plugging on like this.
So I began dissecting the process between source Lab and print density, trying to isolate and understand each factor and function that intervenes along the way.
And because I don�t have a computer science background I end up doing a lot of tail chasing.
The first dragon I encountered was black point compensation. I was already perplexed by this function even before I began testing. When I first read Fraser & Blatner Real World Photoshop 7 I couldn�t figure out why, if this option worked as they said it did, well enough to recommend its systematic usage, they devoted an entire chapter to targeting files to the maximum shadow point of the output device?
It is very likely that what I am describing is common knowledge here, so I wont bore you further by including all of my test data. But should anyone require it to better understand the conditions and settings of my tests I can provide it. I have tested RGB type large and small format archival and dye-based ink jet printers all the way to printed patches.
I find that Black Point Compensation with perceptive rendering intent is redundant , only the slightest deviations occur, if any, and those usually a long way up the curve. The mapping of L*0 is never different.
Secondly , I find that using BPC with relative intent maps L*0 to a density above maximum black.
I anyone can confirm or explain my findings I would greatly appreciate it.
Thank you
JSwift
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