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
	
Thanks!  I have a new printer and new (for me) inkset.  This is going 
to save me a lot of time!

I tested it with my scanner (calibrating using GretagMacbeth step 
wedge) and the results are better than my first 'eyeballed' Dot Gain 
Curve.  Now all I have to do is cancel my anniversary and find someone 
to sell me a spectrophotometer.

--
Kevin