# Why 'more or less stopped using ISO'?

Started Feb 19, 2014 | Questions thread
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 Re: Maybe this will help. In reply to jackdan, Feb 23, 2014

jackdan wrote:

bobn2 wrote:

jackdan wrote:

bobn2 wrote:

jackdan wrote:

bobn2 wrote:

jackdan wrote:

bobn2 wrote:

crames wrote:

bobn2 wrote:

How does brightness figure into this? That is, CIE brightness, or are you using another definition?

I don't see how the connection between luminance and brightness would cause there to be "no such thing as ISO."

You can calculate a brightness for an sRGB value of 118, since the viewing conditions are defined and you have enough info to plug into a CIECAM02 calculator.

What would be the brightness for an sRGB value of 118, in candela per square metre?

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Bob

CIECAM02 brightness correlate Q of the 8 bit sRGB value (118,118,118), Q=102.28.

Candelas per square meter are the units for luminance, not the unit-less brightness, so your question doesn't make sense.

You're obviously fishing around for something, without explaining how brightness, that is CIE brightness as discussed in this sub-thread, has anything to do with the existence or non-existence of "ISO."

Apparently "'brightness' is dependent on 'absolute luminance of the stimulus' ".

While you mull things over,

Sorry, you have the mulling the wrong way round. It's you that needs to be mulling. Apparently 'brightness' is dependent on 'absolute luminance of the stimulus' and yet we find that 'brightness' has nothing to do with luminance, so mull that one over.

I found the post where your "Apparently 'brightness' is dependent on 'absolute luminance of the stimulus' " originated, but have not found the origin of "'brightness' has nothing to do with luminance,". Can you point me to that post please?

It came from you, 'candelas per square meter are the units for luminance, not the unit-less brightness'.

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Bob

I am guessing you thought I was someone else. What I said was, "So although there are no units for brightness there are units for the measurment of the perceived brightness to the human eye." Those units, of course, being for luminance".

I probably have got confused between you and crames.

Crames is the one who know what he is talking about.

I'm sure he does, but he doesn't appear to be able to make the right connections in this case.

My impression is that crames always adhered to good science and that you didn't always realize when he was talking within the confines of a specific color model, although he always made it perfectly clear.

He seems to know his colour models. I'm not as clear that he understands the physical significance of those colour models.

I was also disappointed that you have gone to great lengths to avoid his outstanding unanswered question.

Which outstanding question? So far as I know, I've answered all his questions.

You have also avoided answering my question,

"...but have not found the origin of "brightness' has nothing to do with luminance". Can you point me to that post please?.

I answered your question too, if you wish to pretend otherwise, that is quite up to you.

So, the units for measurement of the perceived brightness to the human eye are candela per square metre? Really?

Only in so far as "luminance is the measurable quantity which most closely corresponds to brightness."

(Brightness, Luminance, and Confusion. from Information Display March 1993 (vol . 9, iss. 3, pp. 21-24). By Charles P. Halsted )

Well, yes - but 'most closely corresponds' is hardly a tight relationship

Well "Photometry is the science of the measurement of light in terms of it's perceived brightness to the human eye" and those measurements have units. The relationship between the measured quantity and brightness is what it is and the definition for photometry probably expresses it best.

What is that relationship? There must be a function that maps 'luminance' to 'brightness'. What is it?

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Bob

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