Why 'more or less stopped using ISO'?

Started Feb 19, 2014 | Questions thread
crames Regular Member • Posts: 192
Re: Maybe this will help.

Luke Kaven wrote:

crames wrote:

Only if you know how to convert to XYZ, where Y is luminance. CIE states that brightness is relative luminance. Relative luminance is defined as photometric luminance normalized to 0..100 in such a way that reference white is 100.

No, Brightness is an absolute percept, not relative. Relative Brightness is called Lightness.

If you're working in HSV, to be sure.

HSV is used for computer graphics. It's not a real color space and has nothing really to do with lightness or brightness.

If you're a conceptual analyst then you can argue that this is a technical definition of the term 'brightness' bearing a metaphoric-at-best relationship to the ordinary language term "brightness", which is primal.

They are technical terms defined in the CIE International Lighting Vocabulary, as used in color science and engineering.

If you're an engineer, then you can argue that there's no significant difference between the two things by appeal to the argument-from-authority (e.g., "a standards organization said so").

If you're talking CIE, XYZ, luminance etc. etc. really only the CIE definitions make sense. These are the definitions of the organization that brought us CIELAB, CIECAM02, the Standard Observer, XYZ.

From Colour Engineering, Wiley 2003:


"This is a visual perception according to which an area appears to exhibit more or less light. This is an open-ended scale with a zero origin defining the black.

"The brightness of a sample is affected by the luminance of the light source used. A surface colour illuminated by a higher luminance would appear brighter than the same surface illuminated by a lower luminance.


"This is the brightness of an area judged relative to a brightness of a similarly illuminated reference white.

"The lightness scale runs from black, 0, to white, 100. The lightness of the background used can cause a change in the lightness of the sample..."

These are not highly technical definitions! Lightness and brightness are distinctly different perceptions and are not interchangeable.

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