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After the discussion on UV density and the profile posted by Sandy King and the paper and files of Michael Rosenberg, I have been making some progress with my curve but now I am stuck as it seems that no matter what I enter in GRAY_CURVE has any effect. I tried both inserting an acv file (created in CS6) or values in the format "xx;yy xx;yy etc" but the step wedge printed does not show any difference from the one printed without a curve.
Also when I load the profile with the curve (created in CS6) I get this error (this is why I tried to enter the values manually):

As a further test I generated quad files from the same profile without curve, with the curve as acv, and as text directly in the profile. I then compared the resulting quad files (renamed) and they were all exactly the same as the quad with NO curve. I am not sure about the validity of this test since I don't know the inner workings of QTR, but I think I am doing something is wrong.
The profile I am using is:

PRINTER=QuadR2880
CURVE_NAME=r2880-gum-FaGF-WN-PM-v4-curve
GRAPH_CURVE=YES
N_OF_INKS=8
DEFAULT_INK_LIMIT=55
BOOST_K=0
LIMIT_K=5
LIMIT_C=5
LIMIT_M=1
LIMIT_Y=5
LIMIT_LC=10
LIMIT_LM=1
LIMIT_LK=15
LIMIT_LLK=1
N_OF_GRAY_PARTS=0
GRAY_HIGHLIGHT=0
GRAY_SHADOW=0
GRAY_OVERLAP=100
GRAY_GAMMA=1
GRAY_CURVE=test1.acv
N_OF_TONER_PARTS=0
TONER_HIGHLIGHT=10
TONER_SHADOW=10
TONER_GAMMA=1
TONER_CURVE=
N_OF_TONER_2_PARTS=0
TONER_2_HIGHLIGHT=10
TONER_2_SHADOW=10
TONER_2_GAMMA=1
TONER_2_CURVE=
N_OF_UNUSED=0
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

I have used several versions of this profile to print on regular photo paper instead of OHP to be able to scan the page and measure the changes. I have one step wedge printed with one of the older profiles so I can guesstimate what it's going to happen.
After scanning the step wedge, I open it in CS6, convert it to LAB and keep only the L channel, convert back to RGB, adjust Levels so the 0% and 100% step are indeed at that value, and read all the other steps.
I am basically following the procedure described by Ron Reeder.
My readings are:
IN OUT
0 0
5 4
10 14
15 25
20 35
30 51
40 65
50 75
60 81
70 88
80 92
85 94
90 96
95 98
100 100

The data to create the curve are then:
IN OUT
100 100
96 95
86 90
75 85
65 80
49 70
35 60
25 50
19 40
12 30
8 20
6 15
4 10
2 5
0 0
Any ideas? I am sure I am doing something wrong!!
Thanks,
Luciano

QTR-Quadtone RIP

Curve in GRAY_CURVE has no effect?

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