measuring luminance

[behrengi]

I want to display isoluminant colors (which are colors that have the same luminance) on my monitor for experimental purposes. To this end, I’m planning to buy a colorimeter (probably x-rite i1 display pro) and I wonder whether I can use DisplayCAL for this. I don’t have an access to a spectrophotometer nor a budget for it.

Here, it says that I either have to use a DKL color space or know the maximum luminance of each color gun (R-G-B separately and in cd/m2).

My questions are:

1. Can I measure maximum luminance of each color gun using a colorimeter and DisplayCal?
2. I’ve seen some pictures here, it seems that DisplayCal can report measured L*a*b* colors, how is L in Lab related to luminance? May I calculate luminance using L?
3. In order to use a DKL space they say I need a DKL to RGB conversion matrix, is it something I can obtain using DisplayCal or calculate using the measures provided?

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[behrengi]

Hello again. I haven’t received any replies to this post, probably because it was awaiting moderation. I would be really happy if someone could help.

[Vincent]

My questions are:

1. Can I measure maximum luminance of each color gun using a colorimeter and DisplayCal?

First of all it is HUMAN luminance. It is weighted against human vision. You can have a huge spike of energy in blue wavelengths… but it will have low luminance for humans.

LCDs have no guns, but yes if you use ArgyllCMS comand line spotread + MS paint with each primary color patch, or making your own testchart for DisplayCAL.
Or HCFR (like DIsplayCAL but for TVs and single spot measurements). It will be easier with HCFR.

1. I’ve seen some pictures here, it seems that DisplayCal can report measured L*a*b* colors, how is L in Lab related to luminance? May I calculate luminance using L?

Luminance is Y value from CIE XYZ or CIE xyY.

[behrengi]

Thank you for your reply.  I still don’t get somethings though, may I ask for some clarifications?

First of all it is HUMAN luminance. It is weighted against human vision. You can have a huge spike of energy in blue wavelengths… but it will have low luminance for humans.

I know perceived brightness can be different and what I am interested in is the amount of light projected from the display. I thought the word “luminance” specifically meant that and was not a subjective measure. Wikipedia seems to agree with me.

LCDs have no guns, but yes if you use ArgyllCMS comand line spotread + MS paint with each primary color patch, or making your own testchart for DisplayCAL.

I am going to use a CRT. But still, by gun I meant separate axes of any chosen color space and perhaps it was a bit misleading. From your reply I understand that I can measure the luminance of whatever color I choose, which means whichever color space I am going to use, I will be able to know the maximum luminance of its axes, right?

Luminance is Y value from CIE XYZ or CIE xyY.

Just to be safe, are the Y values objective measures of brightness? And if yes, can they be obtained with displayCAL and a colorimeter?

[behrengi]

Just to be safe, are the Y values objective measures of brightness? And if yes, can they be obtained with displayCAL and a colorimeter?

Also, is this in cd/m2 or something I can convert to cd/m2?

[Vincent]

“Human” = Y value. For other types of measurement you’ll need an spectrophotometer… and to be accurate it will be expensive. i1Pro2 about 1000 euro.

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