Pages: [1]   Go Down

Author Topic: Calculate Density over C,M,Y,K on 21 step wedge  (Read 913 times)

Erland

  • Full Member
  • ***
  • Offline Offline
  • Posts: 127
Calculate Density over C,M,Y,K on 21 step wedge
« on: February 23, 2017, 11:46:01 AM »

Hi!
I am trying to calculate the Dmax from a measured 21 step wedge over CMYK.
Each color is printed with a range from 0 to 100% over 21 steps, as usual.
I then measure and get a cgats containing LAB and the spectral info on each patch. This I then want to use to calculte the density on each patch.
=ABS(LOG(AVERAGE(380nm:720nm),10))
Is the formula I am trying to use. While it get a good reading over the black patch, the CMY doesn't add up compared to a "regular" density I should get, like C 1.4, M 1.2, Y 0.95(ish).
I want to use an own spreadsheet so I can import the data from each new .txt file I get. So I can't use bruces spreadsheet for 10nm.

I would appreciate some help from you guys if you could.
Kind Regards.
Marcus

Logged
Service Technician Digital Printers and Peripherals.
Epson Stylus Photo 1400.

GWGill

  • Sr. Member
  • ****
  • Offline Offline
  • Posts: 407
  • Author of ArgyllCMS & ArgyllPRO ColorMeter
    • ArgyllCMS
Re: Calculate Density over C,M,Y,K on 21 step wedge
« Reply #1 on: February 23, 2017, 04:39:45 PM »

This I then want to use to calculte the density on each patch.
=ABS(LOG(AVERAGE(380nm:720nm),10))
Density calculations from spectral use weightings, much like the observer weightings used to calculate XYZ.
There are different standards for this for different applications and media (Status A, Status T etc.).

You might find Bruce Lindblooms density calculation spreadsheet is useful for this.
Logged

Tim Lookingbill

  • Sr. Member
  • ****
  • Offline Offline
  • Posts: 2159
Re: Calculate Density over C,M,Y,K on 21 step wedge
« Reply #2 on: February 23, 2017, 08:04:55 PM »

Not sure what the purpose is in why and what you're measuring from whether it's for print predictability using CMYK combos for gray or  for measuring CMYK ramps individually. Is this for inkjet or commercial press? Is this for building a standard test target?

What are you going to use this for? Back in my prepress production days I used what was called a Graphics Master that listed commercial press printed stepwedge ramps for each CYMK 21 step patch including different combos and listed their overall density but not in Lab readouts.

With that in mind this might help... https://www.teamflexo.com/products/spoton/

...from this Google search... https://www.google.com/#newwindow=1&q=Graphics+Master+CMYK+gray+ramp+Luminance+density+values&*
Logged

Erland

  • Full Member
  • ***
  • Offline Offline
  • Posts: 127
Re: Calculate Density over C,M,Y,K on 21 step wedge
« Reply #3 on: February 24, 2017, 03:20:59 AM »

Thanks for input guys. This is a tonerbased machine.

Usually if I do a linearization in an EFI fiery rip I get a graph showing each patch's density.
But this is on another rip, that only outputs a cgats with LAB and spectral data for each patch, and the rip does not have a UI that is able to show a graph.
So I would like to insert it into a spreadsheet and manually get a graph. For troubleshooting issues we think comes from incorrect linearizations.

I can convert it in i1Profiler into a Status T, E, I etc, but this gives a RGB density, and a visible. Usually we only have one value visible, and I don't know which this is. The visible was my first thought, but yellow never got anywhere near 1.0. Can you calculate a combination of the R density, G density and B density?
Logged
Service Technician Digital Printers and Peripherals.
Epson Stylus Photo 1400.

Erland

  • Full Member
  • ***
  • Offline Offline
  • Posts: 127
Re: Calculate Density over C,M,Y,K on 21 step wedge
« Reply #4 on: February 24, 2017, 10:26:01 AM »

Sorry, totally forgot that R, G, B density is directly connected to C,M,Y! Problem solved!
Plotting the density now only involves importing in i1Profiler, exporting into a cgats with Status T and then importing, and graphing..
Logged
Service Technician Digital Printers and Peripherals.
Epson Stylus Photo 1400.
Pages: [1]   Go Up