Re: Linear-light RAW 12bit vs R'G'B' 8bit: how much better is it really?
Re: Linear-light RAW 12bit vs R'G'B' 8bit: how much better is it really?
- Subject: Re: Linear-light RAW 12bit vs R'G'B' 8bit: how much better is it really?
- From: Ray Maxwell <email@hidden>
- Date: Tue, 24 Jul 2007 14:54:10 -0700
<SNIP>
Not to argue, two questions really.
1) I had heard that the tonal response of ink on paper was closer to
1.8 gamma. I've tried to find out how to calculate this, but I can't
find anyone who knows. Do you know, Ray? If you can tell me how I'd
appreciate it.
Ray replies:
I don't know how you would express the gamma of a solid ink on paper???
I can't help here. However, I do know that the original Apple
Postscript Laser Printer did print with a gamma of approximately 1.8 due
to the screening used in this printer. With screen calibration LUT's
you can make a printing system print at any gamma.
The other possibility of where this might have come from, is that when
printing with modern CTP systems you lose the dot gain that comes from
imaging a plate from film. This is usually equal to about 5%. This
means that a typical CTP system has an end to end dot gain of about 15%
to 18% at 150 lpi. Most printers put in a LUT to correct this back to
the more normal 20% to 25% dot gain so that they can print legacy
files. At the higher dot gain the system is more visually linear and
close to a gamma of 2.2
2) Thinking about the quote about linear versus gamma corrected.
Suppose a person walked with the same size steps all the time. If he
walks on a straight road, he takes 256 steps to cover a certain
distance. If the same straight-line distance were covered by a road
that curved - amazingly to exactly display a 2.2 gamma (or non-
linearity) - would it then take this person 2048 steps to go from end
to end? Is this what he means?
Ray Replies:
I am sorry, but I cannot relate to this metaphor. From a energy or
density perspective the steps are not even. From a visual point of view
they are even. The steps are visually even in a gamma 2.2 editing
space. From a density or energy reflected point of view they are not
linear.
Ray Maxwell
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