Digital BW, The Print

Huh! (hits on the brakes, tires squeeling, pulls to the side of 
the road) Um, let's take two steps back here and let me ask this just 
to make sure were all talking about the same thing here. Are you 
trying to find the relationship between the % values on the stepwedge 
with OD measurements? If you are there is absolutely no relationship. 
The % marks are the K values for the Photoshop color picker. Use the 
dropper and pick a spot. If you click on the little window at the 
bottom of the tool bar the picker will come up. In it are the color 
space values and a CMYK % bar. That's what the % values are on the 
step wedge-the K value. This is what the system thinks should be laid 
down to hit that color or in our case density. 

 Paul reported getting close values with a one ink setup and that is 
because the printer would print 50% coverage with one ink(or use CMY)-
 but there's either lots of big dots or a process grey. The quads use 
4 inks (duh) and the plug in tells the printer a whole different 
command for a density target. i.e. Instead of printing 50% coverage 
of a max density ink it would print 100% coverage of a 50% diluted 
ink. This eliminates dots and allow for the smooth transitions 
between densities, the whole point of the quad system. Does that help?

Jeff.


> 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