FotoDave@aol.com
Sat, 22 May 1999 18:43:37 -0400 (EDT)
I can probably make it a case if AOL kicked me out for the 4th time without
retaining my unsent message, but before it does that, let me quickly send
this mail out....
>> Here is a theoretical question for all you digital buffs. I am wondering
how
> it would be possible to assign reflection densities to rgb densities
(photoshop
> densities) in a purely abstract manner.
Hi Adam,
I thought we went through this in one of our personal emails, but maybe we
didn't.
rgb corresponds to transmittance, transmittance = rgb/255. Opacity =
1/transmittance, and density = log (opacity).
But if you check the calibration scale of your imagesetter output, you will
find that it is already well calibrated to the theorectical value. That means
that you don't really have much to calibrate as far as density is concerned.
You only need to calibrate the print process to match the rgb value (if like
you said, you want to print by numbers), but it is also nice to match your
monitor so that you can estimate the final look.
To calibrate your print process, use the calibration steps (or make 5% to
95%, step 5%), output, and make a print and find your range. Adjust your
exposure, chemical, etc. to make the best print.You might find that for a
particular process, you can print from 15% to 85%, for example.
Then calibrate your monitor (start with gamma 1.8, you might even need
slightly lower), so that 15% is white and 85% is black. Then adjust your
image to look best on monitor, then use adjust level to adjust the levels to
15% to 85%. Output this image together with the step.
Double check the image, you should have gradation on both the lower and upper
ends. Now carefully check your 50% against the monitor. You can fine tune
this with a curve or through the clever use of dot gain.
Then you would have a system that work both visually and theoretically.
In summary: the system has actually been calibrated to the theroretical
value. You simply need to calibrate your print process and the monitor to the
values: make print, calibrate and evaluate black, calibrate and evaluate
white, then carefully calibrate and adjust 50% tone (important).
This is a little brief as I am still unpacking, and my place is a big big
mess. I will try to answer (although it might be a little late) if others
have interest or question.
Dave S
This archive was generated by hypermail 2.0b3 on Thu Oct 28 1999 - 21:39:35