Digital BW, The Print

This might help. 
 optical density (OD): For a given wavelength, an expression of the 
transmittance of an optical element. Note 1: Optical density is 
expressed by log10(1/T ) where T is transmittance. (188) Note 2: The 
higher the optical density, the lower the transmittance. Note 3: 
Optical density times 10 is equal to transmission loss expressed in 
decibels, e.g. , an optical density of 0.3 corresponds to a 
transmission loss of 3 dB. Def of optical density.

Jeff




> John,
> You are at the same point as I am. Well, actually I'm a little 
> ahead. The density readings are log to the base 10 so dividing the 
> Dmax by 2 will not give you the expected 50% reading. I am 
currently 
> trying to figure out the math.
> I will let you know when I get there,
> 
> Barry
> 
> --- In DigitalBlackandWhiteThePrint@y..., John Chervinsky 
> <chervinsky@d...> wrote:
> > Hi,
> > 
> > I am attempting to calibrate my printer output using a calibrated 
> X-Rite 810 densitometer.  I am using MIS FS inks through an Epson 
> 1160 onto PhotoRag 308 paper; I am on a Mac computer.  I realize 
> that this question has come up in the past, but practical elements 
> of technique were omitted.  Below you will find the reflective 
> densitometer (visual) output vs a 21 step stepwedge.  I did 
> measurements using both the Randall and Piezography workflows.  If 
> you look at the numbers carefully, you will conclude as to how 
> shockingly non-linear they are.  I would have expected, for example 
> that the 50 % reading would have been close to 1.7/2 = .85.  The 
> Measured value of around 0.6 is WAY off!
> > 
> > Has anyone else had this experience? I would not think that my 
> paper choice would have that much effect.  Are there subtle 
> differences in using a reflective densitometer as opposed to a 
> spectrophotometer to do the measurements? It would seem that for 
> grayscale work that a densitometer should be fine.  Please advise.
> > 
> > Thanks!
> > 
> > -John Chervinsky
> > 
> > 
> > 
> > STEPWEDGE  CONE      RANDALL
> > 100.0     	1.71     	1.77
> > 95.00     	1.54     	1.66
> > 90.00	     1.40     	1.57
> > 85.00	     1.26     	1.45
> > 80.00	     1.15     	1.33
> > 75.00	     1.05	     1.20
> > 70.00     	0.96     	1.07
> > 65.00	     0.86     	0.95
> > 60.00     	0.78	     0.83
> > 55.00     	0.69      0.76
> > 50.00	     0.61     	0.66
> > 45.00	     0.54     	0.58
> > 40.00	     0.48	     0.48
> > 35.00	     0.42     	0.39
> > 30.00     	0.36	     0.32
> > 25.00     	0.29      0.27
> > 20.00	     0.24     	0.21
> > 15.00	     0.19	     0.17
> > 10.00      0.14      0.13
> > 5.00	      0.09	     0.09
> > 0.00	      0.05	     0.05