XYZ values from Colormunky Display

[Leonardo]

Hello,

I’m trying to better understand the absolute black level of my monitor in a physical unit that I can compare in the real world.

By doing a report with DisplayCal and the Colormunky Display I have:

Report on calibrated display device:
17:26:03,404 Setting up the instrument
17:26:03,404 Product Name: Colormunki Display
17:26:03,404 Serial Number: ———————-
17:26:03,404 Firmware Version: v2.28
17:26:03,404 Firmware Date: 29Jan14
17:26:03,404 Current calibration response:
17:26:03,404 Black level = 0.2715 cd/m^2
17:26:03,404 50% level = 59.13 cd/m^2
17:26:03,404 White level = 279.45 cd/m^2
17:26:03,404 Aprox. gamma = 2.24
17:26:03,404 Contrast ratio = 1029:1
17:26:03,404 White chromaticity coordinates 0.3131, 0.3314
17:26:03,404 White Correlated Color Temperature = 6468K, DE 2K to locus = 5.9
17:26:03,404 White Correlated Daylight Temperature = 6469K, DE 2K to locus = 1.5
17:26:03,404 White Visual Color Temperature = 6259K, DE 2K to locus = 5.7
17:26:03,404 White Visual Daylight Temperature = 6420K, DE 2K to locus = 1.4

By measuring with Argyll spotread utility I have these results:

calibrated profile:
BLACK XYZ: 0.302212 0.271674 0.655879, D50 Lab: 2.454025 1.625821 -8.151798
WHITE XYZ: 264.077642 279.491549 300.454245, D50 Lab: 147.398306 -4.743947 -25.998078

So contrast = 279.491549 / 0.271674 = 1029 : 1 agree with the displayCal report.

What I don’t agree is the D50 Lab value for the BLACK. An L* value of 2.45 is very low and seems can’t be compared with a spectrophotometer printed BLACK that usually is > 15.
Is there a way to compare emissive (ex. display) measurements with reflective (ex. paper) measurements?

Thank you

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[Vincent]

Is there a way to compare emissive (ex. display) measurements with reflective (ex. paper) measurements?

Calibrate white to same color as light source for print (numeric or visual), including brightness (500lux ~ 160nit in display, PI * nit = lux as first aproximation)
Then you can match specific a*b* for paper color or use PS “simulate paper white”, and match black by simulating ink (which destroys contrast)
Or if you wish to use LUT3D approach the same but it is more dificult to get a color match visually (but if you use LUT3D beware double color management, it may be easier to test on Paint + DWMLUT)

L* 15 seems typical for a matte paper. Also if you use PS, you can try to swicth to white theme since if you have a light booth, light booth color will look cloter to PS screen and if you keep dark theme “ink simulation” MAY look too much lifted in black but it is apparent due top dark theme.

• This reply was modified 6 months ago by Vincent.

[Leonardo]

Hello Vincent,

My monitor is calibrated to 6500K as you can see from the report. I’m comparing D65 LAB values from the Spectrophotometer, so white reference should be pretty close.

What do you mean with including brightness? I’m mainly interested in comparing the L* value.

Maybe I’m close to the solution:

For the Spectrophotometer L* is related to reflectivity of the object at different wavelenghts. For example L* of 100 means a fully reflective material, L* of 0 is a material that is not reflecting anything in the visible range.

For the Colorimeter (ColorMunki Display) L* is the measured cd/m^2.

To have a matching L* I think that I have to convert from cd/m^2 to a kind of reflectivity, but I’m not sure I’m on the right track.

[Vincent]

Hello Vincent,

My monitor is calibrated to 6500K as you can see from the report. I’m comparing D65 LAB values from the Spectrophotometer, so white reference should be pretty close.

No, unless you have a D65 simulation light source (a pro lightbooth for clothing for example)

What do you mean with including brightness? I’m mainly interested in comparing the L* value.

That if you wish a visual match “and assuming that there is no other failure”, you must set as display whitepoint the color of the lightspurce and match brightness: PI * nit = lux as first aproximation

Then you can use softproof or LUT3D approach to simulate printed black and paper color using your paper-printer profile.

An example, let’s say that I have ideal instrumenst and not metameric failure at all. I have printer profile for my paper created under tupical illuminant D50.
-I have a light booth with normalized light which is a good simulation of D50
-i set my light booth to 320 lux at paper location
-calibrate display to D50 and “320/pi” nits as first aproximation (100nit, 500 lux => 160nit)
-i have a dry print printed with my printer useing my custom profile
-I open Photoshop, open my image, and using photoshop softproof + simulate paper color + similate ink.
=> displayed image and printed image match.

That’s is an ideal behavior, maybe you must tune a little brightness (booth or display) or paper color (display)

So if your matte paper profiled for your pinter says L* 15 for black, once you use Photoshop softpoof with simulate ink it will simulate taht blakc on display. You may want to set PS UI theme to “light grey” if your booth is very light grey.
If you do not use PS but want a custom color simulation you can use DWMLUT on non color managed viewer.

in othe words, unless you use softproof you cannot compare “common display color management” and printed values

Maybe I’m close to the solution:

For the Spectrophotometer L* is related to reflectivity of the object at different wavelenghts. For example L* of 100 means a fully reflective material, L* of 0 is a material that is not reflecting anything in the visible range.

For the Colorimeter (ColorMunki Display) L* is the measured cd/m^2.

To have a matching L* I think that I have to convert from cd/m^2 to a kind of reflectivity, but I’m not sure I’m on the right track.

Explained above and in previous message

[Leonardo]

Hello,

I don’t have a lightbooth or Photoshop installed, but I found a 5000k led light with CRI>98 that approximates someway a D50 light. The spectral chart of the led seems very close.
I understand that things get pretty complex. To simplify things let’s say I want to match a flat object color with the monitor. In this way we can keep the Printer / Paper profile, Photoshop, etc.. out.

The workflow I understood in this case is:
– Calibrate the Monitor for D50 with the ColorMunki Display
– Measure the object color with a reflection spectrophotometer (ex. Nix Spectro 2) and take the D50 reading
– Display the measured color on the monitor and adjust the brightness to match the D50 led light
– Check with the ColorMunki Display that the displayed color match the reflection spectrophotometer LAB values (L* is different because is matching the led light)
– Compare the physical color sample under the D50 led light with the color displayed on the monitor, should be very similar (apart perception things).

Note: I used the ColorMunki to measure the ambient LUX on my color samples and I tried to match the same illumination on the monitor. I have 750 LUX at a distance of 35 cm from the light.
From you formula, to see the same brightness on the monitor I should set it to around: LUX / 3.14 = 239 nit

Thanks again

[Vincent]

– Display the measured color on the monitor and adjust the brightness to match the D50 led light

Without proper software you need to do L*a*b* (measured object color relative to its illuminant) => RGB in display colorspace.
Maybe using https://www.argyllcms.com/doc/xicclu.html on display colorspace (profile).

That’s why it’s better to use color managed software like PS.
GIMP color management is very limited, you can’t trust the color picker. There is an older fork GIMP ColorCorrectedEdition (CCE) 2.9.5 whcih worked as expected. I have not testetd krita or other software for a while so IDNK for them.

– Check with the ColorMunki Display that the displayed color match the reflection spectrophotometer LAB values (L* is different because is matching the led light)
– Compare the physical color sample under the D50 led light with the color displayed on the monitor, should be very similar (apart perception things).

Note: I used the ColorMunki to measure the ambient LUX on my color samples and I tried to match the same illumination on the monitor. I have 750 LUX at a distance of 35 cm from the light.
From you formula, to see the same brightness on the monitor I should set it to around: LUX / 3.14 = 239 nit

Thanks again

[Leonardo]

Hello,

I used Affinity Designer (that’s based on LittleCMS) to display the color.

I double checked the displayed color with the ColorMunky Display and ArgyII spotcolor -ew to be sure that something was not wrong somewhere in the software chain. I used an rgb 255,255,255 for the reference white and then I measured my color generated by using the LAB color picker entry. The measured color was pretty close.

[Author]

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