Determining tonal percentage?
Determining tonal percentage?
- Subject: Determining tonal percentage?
- From: Tyler Boley <email@hidden>
- Date: Thu, 24 Apr 2003 11:44:54 -0700
I keep running into the same wall, using density measurements to
linearize monochromatic printing with quadtone inks in Epsons. There
seems to be a disconnect between the prepress/color management world and
the photography world with regard to numeric representation of density
percentage on paper. I realize dot gain, dot area, etc. are very
specific terms that I may be using erroneously.
All the tools I've tried, the Spectrocam dot gain software, the
Murray-Davies spreadsheet, and Bruce Lindbloom's density calculator all
seem to agree with each other more or less, so I assume they all adhere
to the same standards. But they all give (for an approximate example) a
reading of about 71% for a value I (a photographer) would call
approximately 50% on paper. Conversely, working in the opposite
direction, if I use these tools to tell me which of my printed ink
patches to map to 50%, it looks to me to be around 32% gray on paper.
I get something much closer when I enter a value of around 2.2
(coincidence?) for the mysterious N factor in Murray-Davies. What is the
N factor, and why is there a purely arbitrary factor in a calculation
used for such a specific and precise purpose? And where in the world did
Kodak come up with 18% as middle gray? Obviously my lack of knowledge is
screaming out loud here, and those last questions are merely interesting
and not to the real point. Murray-Davies gets me close, but the
arbitrary N factor leads me to think it's still too subjective. I'd
prefer to nail this.
Are there mathematical standards I can use to determine, knowing my ink
dmax and paper white, to use measurement data to linearize monochromatic
output by photographic standards? There must be some connection, in
Photoshop (for example) 50% gray is "middle" gray. There is obviously a
critical hole in my knowledge, or a basic mistake
Thank you so much.
Tyler
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