BPC
BPC
- Subject: BPC
- From: "John Swift" <email@hidden>
- Date: Tue, 27 Apr 2004 13:03:18 -0400
I am attempting to construct a table to correlate Lab values and print
densities to enable me to better target files for different devices.
I am trying to determine the LAB values of the maximum shadow and minimum
highlight points of these output spaces, and, am wondering about the
usefulness of Black Point Compensation to that end. I have found it almost
impossible to ascertain the maximum shadow and minimum highlight points of a
device using soft proofing, or reading a file converted into the output
space.
I would have expected that a conversion using colorimetric relative with
black point compensation would show the real maximum shadow of the output
device. Am I wrong about this? The conversion of L*0 (source) to the printer
profile using relative with Black Point Compensation does produce higher
values than the other three variables, ( relative without BPC and perceptive
with and without BPC), which would tend to suggest that this is the real
lab value for the minimum shadow. However when the patches are printed they
confirm that the value for L*0 after converting with relative and BPC is
actually lighter than maximum black.
The real example of this is as follows
A patch in RGB Source is L* 1 against L* 0
using Perceptive with and without BPC or relative without BPC, values read (
L*4 against L* 4) and the patch prints no line.
using relative with BPC the values read L*10 on L* 7, the patch prints a
line, however the density of the tone that this conversion reads as
(L*0=L*7) is lighter than the tone that the above conversion read as (L*0=L*
4) which really was maximum black.
Can I trust the tools Photoshop provides for accurate readings of post
conversion Lab values? Is this simply a problem of the unreliability of lab
values lower than 10 or is there something I am not understanding about
black point compensation?
JSwift
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