Digital BW, The Print

----- Original Message -----
From: "Kevin Gulstene" <kevin@...>
To: <DigitalBlackandWhiteThePrint@yahoogroups.com>
Sent: Monday, March 17, 2003 11:26 PM
Subject: Re: [Digital BW] Re: FS MIS + Piezo


> Martin-
>
> >
> > If you have access to a densitometer you can take readings from
> > printed step
> > wedges and create pretty accurate curves for soft proofing.
>
> Can you elaborate on how you do this?  What do you relate the density
> measurement to?
>

Kevin,

You print out a standard 21-step wedge using the paper, ink and workflow you
want to use. You then measure all the steps in the wedge that correspond to
the adjustment points available in the Custom Dot Gain curve: 2%, 4%, 6%,
8%, 10%, 20%. 30%, 40%, 50%, 60%, 70%, 80% and 90%. There are no values on
the current step wedge for 6% and 8% but you can safely ignore those as the
other 12 points seem to be good enough for soft proofing.

Some spectrophotometers and their software will give you Dot% values
directly. If all you can read is reflectance than you have to calculate
them. This gets a bit thick but you can set it up in a spreadsheet program.

Dot% = (1-10^-(D-Dmin))/(1-(10^-(Dmax-Dmin)))

Where D is the density of the particular patch you measured, Dmin is the
density of paper white and Dmax is the density of pure black.

The equation is this complex because density is a calculated value:

Density = log(1/R)

Where R= Reflectance, a percentage value of the amount of light reflected
from a surface.

I have posted an Excel spreadsheet in Files>Image Processing with some
sample density values I got from a FS step wedge awhile back.

Martin Wesley