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Author Topic: converting from prophoto to sRGB: tip  (Read 30974 times)
Eric Myrvaagnes
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« Reply #60 on: November 26, 2007, 03:22:10 PM »
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As far as I can see (ouch: pun) from following this discussion, the only definition of color that is precisely defined is one that requires the word "color" to be applied only to those visual sensations that can be seen by all persons. Since that must include those who are totally blind, clearly the set of "colors" is the empty set.

Ergo, there are no colors!    
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papa v2.0
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« Reply #61 on: November 26, 2007, 03:27:05 PM »
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In a dark room, I can faintly see the emissions of some IR remote control LEDs (same with the IR data port on some Palms & laptops), and can tell when a button is being pressed or data is being transmitted. Many people cannot. Is IR a color then, or not? I can see it, poorly, yes, but some IR falls within my range of visual perception.
[a href=\"index.php?act=findpost&pid=156175\"][{POST_SNAPBACK}][/a]

Very interesting!

Which LEDs are these, and what are their IR wavelength range. Can you specify the manufacture.
I would like to measure them as see exactly what spectral radiation they are emitting.

What is probably happening is that the LED is giving off both IR and visible wavelengths.

also
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'I'm pinging a color scientist on this. It will be interesting to hear what they have to say about this (science or semantics)?'

MMM should be very interesting


also

" Visible color as defined by the CIE, not necessarily everyone on the planet. The Standard Observer if you will. "

Is this discussion not about ROMM  a colour encoding space derived from CIE colorimetry??

and finally

"Given that, I think it's a bit narrow-minded to define a "color" as something perceivable by human vision,..."

What or how would you define 'colour' then?    This will be most interesting!
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digitaldog
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« Reply #62 on: November 26, 2007, 03:28:40 PM »
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As far as I can see (ouch: pun) from following this discussion, the only definition of color that is precisely defined is one that requires the word "color" to be applied only to those visual sensations that can be seen by all persons. Since that must include those who are totally blind, clearly the set of "colors" is the empty set.

Ergo, there are no colors!   
[a href=\"index.php?act=findpost&pid=156208\"][{POST_SNAPBACK}][/a]

And my tech editor (and a color scientist who I asked) agrees with you sort of (and papa)

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Color, is a perceptual property. So if you can't see it it's not a 
color. Color is not a particular wavelength of light. It is a 
cognitive perception that is the end result of the excitation of 
photoreceptors followed by retinal processing and ending in the 
visual cortex. We define colors based on perceptual experiments.

A coordinate in a "colorspace" outside the spectrum locus is not a 
color.
We often refer to these as "imaginary colors" but this is by 
and large also erroneous (you can't map an imaginary color from one 
colorspace to another as the math (and experimental data) for each 
colorspace breaks down outside the spectrum locus.

No one sees IR. Most IR LEDs have minor output in visible wavelengths 
as well as IR.


Karl Lang

I learn something new and useful every day!
« Last Edit: November 26, 2007, 03:29:19 PM by digitaldog » Logged

Andrew Rodney
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papa v2.0
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« Reply #63 on: November 26, 2007, 03:58:03 PM »
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Hi

Thanks Digital Dog and Jonathan Wienke for a stimulating and well mannered discussion.

Next!

Cheers, Papa v2.0
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Eric Myrvaagnes
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« Reply #64 on: November 26, 2007, 11:21:16 PM »
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Color, is a perceptual property. So if you can't see it it's not a 
color.
Well, I'm willing to concede that Karl Lang knows more about the subject than I do. But I still have one nagging question: If person A (not blind) can see a certain wavelength of light, but person B (also not blind) cannot, is there still a color here?

As an individual with a fairly common form of color-blindness (generally called "red-green"), I know that there are portions of the "visible" spectrum that are not visible to my eyes. Are those colors, or are they perhaps "semi-colors"?
« Last Edit: November 26, 2007, 11:47:05 PM by EricM » Logged

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Ray
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« Reply #65 on: November 27, 2007, 12:44:54 AM »
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Quote
Color, is a perceptual property. So if you can't see it it's not a 
color.
Well, I'm willing to concede that Karl Lang knows more about the subject than I do. But I still have one nagging question: If person A (not blind) can see a certain wavelength of light, but person B (also not blind) cannot, is there still a color here?

As an individual with a fairly common form of color-blindness (generally called "red-green"), I know that there are portions of the "visible" spectrum that are not visible to my eyes. Are those colors, or are they perhaps "semi-colors"?
[a href=\"index.php?act=findpost&pid=156314\"][{POST_SNAPBACK}][/a]


I think the essential point here is that color is a subjective phenomenon. It has no objective reality specifically as a color. It has an objective reality as an electromagnertic wave length, or as a mathematical construct.

It is claimed that some species of birds, colorful birds of paradise, can see another primary in the ultraviolet region. We have no way of knowing what such a 4th primary would look like. In fact we have no way of knowing if one person's sensation of say red is the same as another person's. We usually refer to such subjective responses as qualia.
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bjanes
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« Reply #66 on: November 27, 2007, 06:59:16 AM »
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I think the essential point here is that color is a subjective phenomenon. It has no objective reality specifically as a color. It has an objective reality as an electromagnertic wave length, or as a mathematical construct.

It is claimed that some species of birds, colorful birds of paradise, can see another primary in the ultraviolet region. We have no way of knowing what such a 4th primary would look like. In fact we have no way of knowing if one person's sensation of say red is the same as another person's. We usually refer to such subjective responses as qualia.
[{POST_SNAPBACK}][/a]

[a href=\"http://en.wikipedia.org/wiki/Color_vision]Wikipedia[/url] has an interesting article on color vision. If you look at the graph of the spectral response of the human eye, you will see that there is a gap between the S (blue) and M (green) spectra. There was an interesting article in Scientific American a couple of years ago discussing the evolution of these sensors. Some animals (birds I think) have a fourth sensor in this gap, and human precursors apparently did also, but it was lost in evolution. Some mammals are dichromats and others have no color vision.
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digitaldog
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« Reply #67 on: November 27, 2007, 08:15:58 AM »
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If person A (not blind) can see a certain wavelength of light, but person B (also not blind) cannot, is there still a color here?

There is color for person A and no color for person B. Karl's point (and now that I think of it, Bruce Fraser once said), color is something that happens in our brains. The brain of person B doesn't 'see' the color, thus there isn't a color.

At the end of the day, it doesn't matter. We're just battery food in the Matrix <g>
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Andrew Rodney
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boffellid
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« Reply #68 on: November 27, 2007, 04:16:53 PM »
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For those interested in the biology of color perception, a great introduction can be found in 'Vision and Art: The Biology of Seeing', by Margaret S. Livingstone. The author is a Harvard neurobiologist, but the book is very simply written and beautifully illustrated.

Dario
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papa v2.0
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« Reply #69 on: November 27, 2007, 08:05:41 PM »
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'Wikipedia'...

is probably the last place  you want to quote from,  if one wants to enter any sensible discussion or to be taken seriously.
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bjanes
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« Reply #70 on: November 27, 2007, 10:04:36 PM »
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'Wikipedia'...

is probably the last place  you want to quote from,  if one wants to enter any sensible discussion or to be taken seriously.
[{POST_SNAPBACK}][/a]

A recent comparison by the highly respected UK journal [a href=\"http://news.bbc.co.uk/1/hi/technology/4530930.stm]Nature[/url] of Wikipedia to Encyclopedia Britannica showed that Wikipedia was about as accurate on scientific subjects as the more established publication. In recent threads Wikipedia has been quoted by Andrew Rodney, Jeff Schewe and others who expect to be taken seriously.

For serious scholarly publications the author would most likely refer to primary sources and not an encyclopedia, and Wikipedia is not allowed to be referenced by many universities. However, the article I cited above is perfectly suitable for this forum. Please shoe me where the article is in serious error.
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Ray
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« Reply #71 on: November 28, 2007, 09:57:16 PM »
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Wikipedia has an interesting article on color vision. If you look at the graph of the spectral response of the human eye, you will see that there is a gap between the S (blue) and M (green) spectra. There was an interesting article in Scientific American a couple of years ago discussing the evolution of these sensors. Some animals (birds I think) have a fourth sensor in this gap, and human precursors apparently did also, but it was lost in evolution. Some mammals are dichromats and others have no color vision.
[{POST_SNAPBACK}][/a]

It's seems there's quite a bit of ongoing research taking place regarding these additional color sensitivities. It's not only some birds of the feathered variety who can see a fourth primary but some birds of the homo sapien variety also.

Refer this article at [a href=\"http://ray.tomes.biz/b2/index.php/a/2007/06/21/p147]http://ray.tomes.biz/b2/index.php/a/2007/06/21/p147[/url]

In fact, it seems that some birds of the feathered variety can not only see a fourth primary between the current blue and green wavelengths, but a fifth primary in the ultra-violet region. They are pentachromats.

Simplified, we have some colorblind men who are dichromats; most of us who are trichromats; the occasional woman who is a tetrachromat, and some species of birds and butterflies who are pentachromats.
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papa v2.0
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« Reply #72 on: November 29, 2007, 07:39:58 AM »
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Please shoe me where the article is in serious error.
[{POST_SNAPBACK}][/a]

[a href=\"http://en.wikipedia.org/wiki/Color_vision]http://en.wikipedia.org/wiki/Color_vision[/url]

Wikipedia states

'three things are needed to see color: a light source, a detector (e.g. the eye) and a sample to view.'

you can see colour with only two things!

As in the case of emmissive light or blackbody radiation - source and detector

See what I mean about Wikipedia
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Eric Myrvaagnes
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« Reply #73 on: November 29, 2007, 09:55:12 AM »
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http://en.wikipedia.org/wiki/Color_vision

Wikipedia states

'three things are needed to see color: a light source, a detector (e.g. the eye) and a sample to view.'

you can see colour with only two things!

As in the case of emmissive light or blackbody radiation - source and detector

See what I mean about Wikipedia
[a href=\"index.php?act=findpost&pid=156928\"][{POST_SNAPBACK}][/a]
Nonsense. You'r simply saying that two of the three might be the same thing. If I'm looking at a light source, the light source is also the sample.
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-Eric Myrvaagnes

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Ray
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« Reply #74 on: November 29, 2007, 10:23:53 AM »
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Nonsense. You'r simply saying that two of the three might be the same thing. If I'm looking at a light source, the light source is also the sample.
[a href=\"index.php?act=findpost&pid=156959\"][{POST_SNAPBACK}][/a]

That's what I thought, Eric, but wasn't able to express it so succinctly.  
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papa v2.0
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« Reply #75 on: November 29, 2007, 10:33:00 AM »
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no
using the eye as the detector
colour can be seen from a blackbody radiator  (two things) and also from a surface reflection (three things)
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Jonathan Wienke
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« Reply #76 on: November 29, 2007, 10:56:43 AM »
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no
using the eye as the detector
colour can be seen from a blackbody radiator  (two things) and also from a surface reflection (three things)

Given that the vast majority of objects in the universe are not luminous in the visible spectrum, I think that characterizing the Wikipedia article as "inaccurate" is pedantic nitpicking. Incomplete (for not listing the an exception for luminous objects) perhaps, but not inaccurate.
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bjanes
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« Reply #77 on: November 29, 2007, 11:52:00 AM »
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Nonsense. You'r simply saying that two of the three might be the same thing. If I'm looking at a light source, the light source is also the sample.
[a href=\"index.php?act=findpost&pid=156959\"][{POST_SNAPBACK}][/a]

A further riposte to Papa:

If you want to nit-pick even further, color is a perception that occurs in the brain. The eye is only a sensor that transmits tri-stimulus color information to the brain, where it is processed, resulting in the perception of color. The eye may be working properly in a comatose person, but there will be no perception of color.

However, when presenting information to a general audience, some simplifications need to be made or else the presentation may be overwhelming. Thus, I am not considering the opponency theory of color, which would only muddle the issue further.

"Small minds are much distressed by little things. Great minds see them all but are not upset by them."

        Francois de La Rochefoucauld
        French author & moralist (1613 - 1680)
« Last Edit: November 29, 2007, 11:56:34 AM by bjanes » Logged
papa v2.0
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« Reply #78 on: November 29, 2007, 01:04:38 PM »
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Given that the vast majority of objects in the universe are not luminous in the visible spectrum,
[a href=\"index.php?act=findpost&pid=156981\"][{POST_SNAPBACK}][/a]

what do you mean by 'not luminous in the visible spectrum'

but to get back to the point  of

"However, the article I cited above is perfectly suitable for this forum. Please shoe me where the article is in serious error.'


Three things are needed to see color: a light source, a detector (e.g. the eye) and a sample to view.

The above statement is not true.
I have identified an error as requested.

And JBANES you are correct in that the eye is only the detector and the "colour" is formed in the visual cortext.  I should have descried the combination as

1. source and 2. observer

or 1. source   2. sample (reflective or transmissive) and 3. observer
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bjanes
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« Reply #79 on: November 29, 2007, 01:52:16 PM »
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"However, the article I cited above is perfectly suitable for this forum. Please shoe me where the article is in serious error.'
Three things are needed to see color: a light source, a detector (e.g. the eye) and a sample to view.

The above statement is not true.
I have identified an error as requested.

And JBANES you are correct in that the eye is only the detector and the "colour" is formed in the visual cortext.  I should have descried the combination as

1. source and 2. observer

or 1. source   2. sample (reflective or transmissive) and 3. observer
[a href=\"index.php?act=findpost&pid=157026\"][{POST_SNAPBACK}][/a]

Is this a serious error? I think not.
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