Message
Re: Using a densitometer to make digital negative curves
2017-02-18 by sanking@...
It is very simple. You just set your densitometer to read density (not Dot Gain), and then set it to Density minus paper so that when you read the 0% patch of your step wedge the density reads 0.00. Density is measured in log (logarithmn) units. If your densitometer does not have a Densithy - Paper setting you will need to measure the base denstiy of the paper, and then subtract that for all of your readings. For LINEARITY to work, Step 0% needs to be entered as 0.00.
Below is an actual profile for one of my carbon tissues that shows how to enter the density values in the profile. Once these are entered you simply save the profile, then run Install. The process takes less than two minutes to complete. Way, way, way easier and faster, and more accurate, then creating a curve with a scanner. Believe me, I know from experience.
If you don't understand log standard I suggest you review it as it applies to photographic sensitometry. Basically, one stop is equal to log 0.30, each step of a 21 step wedge is 1/2 stop, or log 0.15. Density, as used in sensitometry, is the common log of opacity, which in turn is the reciprocal of transmittance (ability of a material to allow light to pass). Opacity of course is the ability of the material to block light. For example, at 50% transmitance the opacity is 2, and the denisty is log 0.3.
But you don't need to understand any of that, just set the densitometer to read density, then set it to read Denisty minus paper white, and place the readings directly into the LINEARIZE command.
Sandy
#PRINTER=QuadR4880
#CURVE_NAME= Carbon100 #Based on Carbon Tissue #238, 7-8 grams/liter of Cal Tint II Lampblack with tissue coated to a wet height of 0.9mm.
#Profile when printing a step wedge gives a DR (density range) of approximately log 2.20.
#With Tissue #238 sensitize with a 4% potassium dichromate solution, diluted 1+1 with acetone, approximately 10 ml per 8X10 sheet, applied in two coatings with a roller. 650 ULF units.
GRAPH_CURVE=YES
N_OF_INKS=8
DEFAULT_INK_LIMIT=100
LIMIT_K=26
LIMIT_C=1
LIMIT_M=1
LIMIT_Y=31
LIMIT_LC=1
LIMIT_LM=1
LIMIT_LK=44
LIMIT_LLK=1
GRAY_HIGHLIGHT=1
GRAY_SHADOW=1
GRAY_GAMMA= 1
CURVE_K= "0;0 100;100"
COPY_CURVE_C=K
COPY_CURVE_M=K
COPY_CURVE_Y=K
COPY_CURVE_LC=K
COPY_CURVE_LM=K
COPY_CURVE_LK=K
COPY_CURVE_LLK=K
LINEARIZE=“0.00 0.03 .13 .23 .35 .43 .53 .65 .69 .76 .85 .92 1.00 1.08 1.14 1.24 1.32 1.40 1.46 1.54 1.60”