Why 'more or less stopped using ISO'?

Started 6 months ago | Questions thread
Luke Kaven
Veteran MemberPosts: 5,116
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Re: Maybe this will help.
In reply to jackdan, 6 months ago

jackdan wrote:

Iliah Borg wrote:

jackdan wrote:

Iliah Borg wrote:

D Cox wrote:

Iliah Borg wrote:

D Cox wrote:

Iliah Borg wrote:

The raw data are brightness values for the array of pixels.

Brightness is human perception. Measurements are not.

Except that human perception starts with measurement in the retina.

But with spectral sensitivities very different from what a has sensor. Brightness is matched to humans, not to camera sensors.

There is a stream of numbers going through from the photodetector to the print.

They are going through human intellect

The brightness of a patch on the print derives from those numbers.

In many different ways, depending on many design and perception factors. As you can't make a universal formula translating the numbers to the brightness there is really nothing we can do.

Federal Standard 1037C, the Federal Glossary of Telecommunication Terms (1996)

brightness: An attribute of visual perception in which a source appears to emit a given amount of light.Note 1: "Brightness" should be used only for nonquantitative references to physiological sensations and perceptions of light. Note 2: "Brightness" was formerly used as a synonym for the photometric term"luminance" and (incorrectly) for the radiometric term "radiance."

But I already asked to provide brightness unit. It did not help

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Please help me to sort all this out. I understand brightness is only a perception of the human eye, but isn't photometry the measurement of light in terms of perceived brightness to the human eye? And doesn't photometry weight actual radiant energy by a lumenosity function that models human brightness sensitivity? And doesn't photometric measurements have units for quantities such as luminance, luminous flux, luminous intensity, and luminous energy?

So although there are no units for brightness there are units for the measurment of the perceived brightness to the human eye.

And isn't that what matters when you are talking about perceived brightness as you and others are here.

Ok, so I have been doing a little google searching and have learned enough to be dangerous and I know because I am not completely stupid in my old age that I am probably missing something obvious, so please help me to understand all this.

Another thing I need help with is that in RGB color space I understand brightness can be quantited. If I understand correctly, and I wouldn't be surprised if I don't, that in RGB color space, whatever that is, brightness is a quantity that is proportional to the magnitude of the pixel value from 0 to 255 is it, for each of the three values for R,B, andd G.

Human judgments about brightness are subject to what are called "context effects", in which the content of the surrounding regions of the stimulus field, or the order of presentation, can significantly affect one's judgment.

See for example Adelson's checker color illusion. There are a number of examples that are similar to this that will affect a subject's judgment:

http://en.wikipedia.org/wiki/Checker_shadow_illusion

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