QTR-Quadtone RIP

Hi all,

I am wondering how the "ideal density" is calculated for (e.g. 21) greyscale steps. I understand that the density is the log of the reciprocal of reflection...

Let's assume the following

Relative reflection density:

Paper white: 0.00D

Maximum black: 1.68D

My assumptions/calculations

This translates into a relative reflection (via 1/10^density) of:

Paper white: 100%

Maximum black: 2.09%

From what I have read "linearization" means that each step of a wedge (same spacing throughout) has the same change in (relative) reflection?

For the above example and a 21 step printout, the change in relative reflection from one patch to the next would be 4.90% (delta=(1-0.0209)/20); or ideal reflection (IR):

Step IR

0 100.00%

5 95.10%

10 90.21%

15 85.31%

20 80.42%

25 75.52%

30 70.63%

35 65.73%

40 60.84%

45 55.94%

50 51.04%

55 46.15%

60 41.25%

65 36.36%

70 31.46%

75 26.57%

80 21.67%

85 16.78%

90 11.88%

95 6.98%

100 2.09%

If I derive densities (second column, My) for all patches from the above assumption (via -LOG10(reflectance)) I end up with the following (third column, ID = stated in ideal_density.pdf that accompanies QTR). There is quite a discrepancy between my results and those given in the PDF).

Step My ID

0 0.000 0.000

5 0.022 0.048

10 0.045 0.098

15 0.069 0.150

20 0.095 0.204

25 0.122 0.260

30 0.151 0.319

35 0.182 0.381

40 0.216 0.446

45 0.252 0.514

50 0.292 0.586

55 0.336 0.662

60 0.385 0.743

65 0.439 0.830

70 0.502 0.922

75 0.576 1.021

80 0.664 1.129

85 0.775 1.247

90 0.025 1.376

95 1.156 1.519

100 1.680 1.680

Question

Where is the mistake with my thinking/calculation?

Unfortunately, none of the documents provide insight into their calculations. The same applies for the "checking your linearization" Excel-file:

Checking your linearization

BTW: The linked Excel-file shows "ideal" density values (in pink). If you copy them to the yellow cells (actual values), the actual curves deviates quite severely from the pink (ideal) curve. A mistake?

I'd highly appreciate if you could shed light on this topic.

Thanks in advance.

Hi Roy,

Until recently I was also under the impression that L stands for Luminosity, but every reference I can find now says it stands for Lightness. Thought you might be interested. 

Cheers,
Keith

Keith Schreiber
jkschreiber.com

> On Jan 31, 2017, at 1:49 PM, Roy Harrington roy@...m [QuadtoneRIP] <QuadtoneRIP@yahoogroups.com> wrote:
> 
> The L of LAB is called Luminosity --- this is the unit linearized by QTR driver.