I’m curious about the RelCol intent mapping of the
gray axis and, specifically, middle gray. To start with, we know several
things that are immutable facts:
RGB = 128,128,128 = middle gray
Reflective Density = 0.78,0.78,0.78 = middle gray
In LAB, a*b* = 0,0 is neutral. It seems that the L value
for middle gray is dependent on the color space.
Given those things, if I profile my printer and I send it a
file that has RGB=128,128,128, I should be able to measure the result with a
reflective densitometer and get 0.78,0.78,0.78. Alternatively, if I
measure the result with a spectrophotometer, I should get a*b* values of 0,0.
But, I don’t. Generally, what I get is a*b*
values that match the paper white value. For example, if paper white is
something like LAB = 96, 0.4, -1.7, then I’ll get a middle gray that is
fairly close to middle gray density of 0.78 but has a color value in a*b* of
0.4, -1.7 (+/- 0.1).
I say generally because I observe this behavior with Monaco
Profiler Platinum on different papers and with different printers. I
remember the last profile I made with Gretag ProfileMaker was off in color and
density but I don’t recall if it matched up exactly with the color of
paper white like the Monaco software seems to be doing.
Now, I can understand that as the L value approaches paper
white, the colors will be more and more influenced by paper white. But at
middle gray, there should be enough ink to produce a color that is
neutral. In fact, I can edit the profile to make it that way. But I
don’t think I should have to do this.
I further understand that Monaco and Gretag have options for
how to handle the gray axis in the Perceptual intent. But I’m
talking about the Relative Colorimetric intent. I would have thought that
RelCol would map a neutral in the image file to a true neutral in the
print. Perhaps I’m wrong.
So, my question is: Is there some standard or
generally accepted practice for RelCol intent that is causing middle gray in
these prints to NOT come out completely neutral, regardless of the paper color?
Michael
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We are what we repeatedly do. Excellence, then, is not
an act, but a habit. - Aristotle