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Imaging Technology: Theory, Alternatives, Practice and Advances. This is a brand independent discussion of theory, process or device. Ignore this forum unless this matters to you!

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  #1  
Old December 18th, 2017, 09:39 PM
James Lemon James Lemon is offline
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Default Color: Fact or Perception?

To each his own but the reality is that colour is not a scientific fact it has everything to with ones own perception and other contributing factors. Everyone sees colour differently and they do fade much quicker than B&W. There are many famous photographers who shoot in jpeg only this preference is not just geared to wedding photographers and such. Have you ever bought a travel magazine and then visit the place depicted in the pictures to see if it is a true representation of the place?


James
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  #2  
Old December 18th, 2017, 10:19 PM
Asher Kelman Asher Kelman is offline
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Default Color: Fact or Perception?

Quote:
Originally Posted by James Lemon View Post
To each his own but the reality is that colour is not a scientific fact it has everything to with ones own perception and other contributing factors. Everyone sees colour differently and they do fade much quicker than B&W. There are many famous photographers who shoot in jpeg only this preference is not just geared to wedding photographers and such. Have you ever bought a travel magazine and then visit the place depicted in the pictures to see if it is a true representation of the place?


James

Hi James,

You raise an important discussion point, accuracy of color.

Color in a photograph is indeed a matter of preference for the nature of what has to be delivered. In the professional work of Nicolas Claris, you could take a color meter to the boat interior and I am pretty sure it would match hue for hue with his printed pictures, at least as close as the master printer, under his direction could deliver.

No one else, except perhaps curators and restorers of National Art Museums or designers in the fashion industry, care that much about accurate color. For most purposes, color is made "to taste" and for the light it will be presented.

So, in a professional bridal or product shoot, there is a lot of experience to shoot accurately. They know what will give a great exposure without significant post processing. So there is no extra posterization or extra jpg artifacts amateurs of enthisiasts might discover, before printing. Generally, one chooses the camera and WB settings in the camera for the out-of-camera-jpg to have the least need for adjustment. This is riunning a labor-intensive business, with low profit margin and makes sense. If one doesnt mess about with a well exposed jpg, it can often delvier everything that's needed.

The wedding photographer with 3 cameras and 3 assistances with 2 cameras each, do not use grey cards or Gretag Macbeth patches with each shoot. The files are processed in the same place, each time and they know the look needed and it is achieved without complexity of multiple layers, masking and the like.

In this case, the color of THAT camera, is what the photgrapher likes and the work flow is never a surprise.

I however, shoot with whichever camera is working well with the lenses I have available. I use a WhiBal grey card or a Passport™ color checker and make a profile to correct the imagesc in RAW processing. But that is not how most pros work. They like the color of that camera and lens and the lab knows the tweaks to please them! But I am not running a business and want to work wherte the light is dim or has an impossibly wide dynamic range, where a lot of post processing can be needed with most cameras.

The best advice for most folk using jpgs is to make sure that one does an in-camera WB-correction and then, keep your hands of that file unless you have a calibrated monitor in a room with no garish colors to reflect on the screen and a low level of incident 5000 degree K, b.g. incident light.

IOW, modern cameras give great color. I try not to touch color of JPGs on my MacBook Pro in the yellow light of the kitchen! Who knows what you will get.
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Last edited by Asher Kelman; December 19th, 2017 at 10:08 AM.
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  #3  
Old December 18th, 2017, 10:50 PM
Asher Kelman Asher Kelman is offline
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Hi Asher

I do know some pros who work much like yourself and set white balance with a card and use expensive color checkers. Our eyes will adapt to brightness easily without us paying much attention so having the proper brightness level set on your screen would be critical. I set mine at about 11 or 12. There are so many different types of lights these days it would be difficult regardless of what equipment you have to set the white balance in some environments. But if the lighting is neutral, not so bad.

James

James,

Yes, viewing light is of critical importance in expensive art prints. Color checkers are not "expensive", and compared to lenses, they can be considered "budget dust"! As I admitted, white balance in camera corrected JPG files can deliver everything a photographer decides until the files are emasculated in Photoshop! If one is going to play much with JPG files, start with RAW, of course.

For color pictures, where the investment in framing and printing is say $400-$1400, the sales price gets to $600 to $,6,000 as a the gallery keeps a portion and there are packing, transport and exhibition costs. if the light is not daylight, then colors look off!

So the light the picture is shown in is always standardized white light, usually at 5000 degrees Kelvin. So we do make sure that we create the print to be appreciated in that color. Now when the customer takes his picture home, yes, he might screw up my colors by having some odd color light. But at least, when the picture is being purchased, the catalog and the screen and the actual print will match closely as technically feasible.

Asher
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  #4  
Old December 18th, 2017, 11:25 PM
Doug Kerr Doug Kerr is offline
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Hi, James,

Quote:
Originally Posted by James Lemon View Post
To each his own but the reality is that colour is not a scientific fact . . .
The people at the CIE will be sad to learn that.

Best regards,

Doug
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  #5  
Old December 18th, 2017, 11:46 PM
Asher Kelman Asher Kelman is offline
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Hi, James,



The people at the CIE will be sad to learn that.

🍃🍃🍃 🤣 🍃



🤕


Doug,

I thought I was going to split my sides laughing!
Asher
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  #6  
Old December 19th, 2017, 06:03 AM
James Lemon James Lemon is offline
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Hi, James,



The people at the CIE will be sad to learn that.

Best regards,

Doug
Doug

Oh? I am sure the CIE understand that the color red is a sensation and not a fact.

https://www.verywell.com/what-is-the...vision-2795831



James
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  #7  
Old December 19th, 2017, 08:57 AM
Doug Kerr Doug Kerr is offline
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Hi, James,
Quote:
Originally Posted by James Lemon View Post
Doug

Oh? I am sure the CIE understand that the color red is a sensation and not a fact.
But of course a sensation is a fact.

I of course understand the point you were making, which is very important. But I took issue with your specific technical statement. And I still do.

Color, although of course defined in a "subjective" way, nevertheless has a scientific definition. Yes, having a specific color is not a simply measurable inherent physical property of a beam of light, as would be. for example, the frequency of an electrical sine wave. But if we know the spectral distribution of energy in that beam, we can then determine, rigorously and objectively, its color, expressible in many ways (the one preferred in scientific work is by the CIE XYZ color space).

Now of course the way that beam of light, coming for example from a tiny area of a photograph, affects the overall impression of the photograph by a viewer is not at all simply relatable to the color of the beam. There is, at the least, the matter of chromatic adaptation (which of course plays a role in the concept of white balance color correction, which is often involved in the whole chain of delivery of a photographic image.

But color itself is a scientifically-defined property.

Best regards,

Doug
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Old December 19th, 2017, 11:31 AM
Jerome Marot Jerome Marot is offline
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Or...

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  #9  
Old December 19th, 2017, 12:45 PM
Doug Kerr Doug Kerr is offline
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Hi, Jerome,

Quote:
Originally Posted by Jerome Marot View Post
Or...

Ah, a quite lovely folklore fetish.

Do you often have to put fresh chicken blood in it? Have it calibrated by a priest?

Best regards,

Doug
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  #10  
Old December 19th, 2017, 03:09 PM
Jerome Marot Jerome Marot is offline
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Do you often have to put fresh chicken blood in it? Have it calibrated by a priest?
Traditionally, a black rooster is used instead of a chicken, but I am not really sure what kind of priest would be competent.
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Old December 19th, 2017, 03:27 PM
Doug Kerr Doug Kerr is offline
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Hi, Jerome,

Quote:
Originally Posted by Jerome Marot View Post
Traditionally, a black rooster is used instead of a chicken, but I am not really sure what kind of priest would be competent.
Good points.

Best regards,

Doug
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  #12  
Old December 19th, 2017, 06:40 PM
James Lemon James Lemon is offline
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Hi, James,


But of course a sensation is a fact.

I of course understand the point you were making, which is very important. But I took issue with your specific technical statement. And I still do.

Color, although of course defined in a "subjective" way, nevertheless has a scientific definition. Yes, having a specific color is not a simply measurable inherent physical property of a beam of light, as would be. for example, the frequency of an electrical sine wave. But if we know the spectral distribution of energy in that beam, we can then determine, rigorously and objectively, its color, expressible in many ways (the one preferred in scientific work is by the CIE XYZ color space).

Now of course the way that beam of light, coming for example from a tiny area of a photograph, affects the overall impression of the photograph by a viewer is not at all simply relatable to the color of the beam. There is, at the least, the matter of chromatic adaptation (which of course plays a role in the concept of white balance color correction, which is often involved in the whole chain of delivery of a photographic image.

But color itself is a scientifically-defined property.

Best regards,


Doug
Doug

"Color is a function of the human visual system, and is not an intrinsic property. Objects don't "have" color, they give off light that "appears" to be a color. Spectral power distributions exist in the physical world, but color exists only in the mind of the beholder"

https://physics.info/color/

James
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Old December 19th, 2017, 07:16 PM
Doug Kerr Doug Kerr is offline
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Hi, James,

Quote:
Originally Posted by James Lemon View Post
"Color is a function of the human visual system, and is not an intrinsic property. Objects don't "have" color, they give off light that "appears" to be a color. Spectral power distributions exist in the physical world, but color exists only in the mind of the beholder"
That is a nice "homey" notion, but in the context of color science it is actually not true. In color science we have taken the notion of color as a sensation and "normalized" it so it can be defined and even measured without benefit of an observer.

if we have the light coming from a source, and there is no human observer, we can rigorously determine its color (by measurement with the appropriate instrument).

Now you might wish to think in terms that such a measurement (only) tells us how an "ideal" human observer, viewing that light beam under certain prescribed conditions, would be expected to perceive it. And I do not argue with that.

Is an acoustic wave in the audible range "sound" if there is no listener to hear it? Yes.

Does a light beam have a "color" if there is no viewer to perceive it? Yes.

Best regards,

Doug
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  #14  
Old December 19th, 2017, 07:44 PM
James Lemon James Lemon is offline
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Quote:
Originally Posted by Doug Kerr View Post
Hi, James,



That is a nice "homey" notion, but in the context of color science it is actually not true. In color science we have taken the notion of color as a sensation and "normalized" it so it can be defined and even measured without benefit of an observer.

if we have the light coming from a source, and there is no human observer, we can rigorously determine its color (by measurement with the appropriate instrument).

Now you might wish to think in terms that such a measurement (only) tells us how an "ideal" human observer, viewing that light beam under certain prescribed conditions, would be expected to perceive it. And I do not argue with that.

Is an acoustic wave in the audible range "sound" if there is no listener to hear it? Yes.

Does a light beam have a "color" if there is no viewer to perceive it? Yes.

Best regards,

Doug
So how do you measure color Doug? Color perception is closely connected to the wavelength of light .

James
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Old December 20th, 2017, 09:31 AM
Doug Kerr Doug Kerr is offline
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Hi, James,

Quote:
Originally Posted by James Lemon View Post
So how do you measure color Doug? Color perception is closely connected to the wavelength of light .
The mechanics may be performed in different ways, but the ideal underlying process is always this:

First we determine (perhaps with a spectrophotometer) the power spectral density (PSD) of the light whose color we wish to measure. That is a curve (often called just "the spectrum" of the light) that shows how the power in the light is distributed by wavelength. We can think of it (slightly imprecisely) as a plot of how much power there is in each of the myriad components of the light at its respective wavelength.

Next we multiply that curve by a standardized curve (also a function of wavelength) called the X matching function curve. The shape of that curve is defined by the CIE.

By "multiplying one curve by another" I mean that at each wavelength we take the value of the PSD and the value of the matching function curve, multiply them together, and plot the result on another curve (also having wavelength as its horizontal axis). After we have done that for every wavelength in the visual range, we have a third curve.

We now integrate that curve (essentially, determine the area under it). That gives us the value "X".

Now we do that same thing using a second standardized curve, the Y matching function curve. The result is the value "Y".

Finally we do that same thing using a third standardized curve, the Z matching function curve. The result is the value "Z".

The values "X", "Y", and "Z" describe the color of the light, under the CIE "XYZ" color space.

************

Now I know you are uneasy with the notion of an "objective" characterization of what we know is a wholly subjective property. Let me try and reconcile those things.

Suppose we have two light beams with different PSDs but the same color (same X, Y, Z values). We would then find that a human observer would perceive each of these light beams as having the same color, but perhaps not quite. The reason it is "perhaps not quite" is of course that the color perception mechanism behaves slightly differently in different humans.

But if we did such a test over a large number of human subjects, we would find that, on the average, the subjects would perceive the two light beams as being "exactly the same color" when their XYZ values were the same. Thus we can reasonably think of the XYZ values of a light beam as being an objective metric of its color.

In fact, these three "matching function curves" were determined by the CIE to bring that situation about. This was done by, in the early 1930s, conducting in effect the inverse of the experiment I describe above with a large number of human subjects. Then, by a very clever mathematical scheme, the three matching curves were devised so that the XYZ measure of a light's color was consistent, on the average, with the color perception of this group of human subjects.

So, is color a property that is defined as a matter of human perception? Absolutely.

And are we able, in an objective way, with instruments and mathematical manipulation, to determine an objective "metric" (in three numerical values) of what should be that human perception of color for a given instance of light for the hypothetical "average human observer".

I hope that helps.

Best regards,

Doug
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Old December 20th, 2017, 09:50 AM
Asher Kelman Asher Kelman is offline
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Doug,

I appreciate your brief essay. Beautiful description. Few can match that clarity!

Can we add some examples for the X, Y,Z calculations to build a few points on charts to create a point in a 3D space 3D space?

Also, how do we reconcile this with the stacked set of circular planes of Munsons color model? How objective is that and is there a version to account for "color spaces"? As that system is so intuitive to the human brain!

Asher
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Old December 20th, 2017, 09:57 AM
Doug Kerr Doug Kerr is offline
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We are often most earnestly interested in the chromaticity of a color, the property that in fact a "civilian" thinks of as "color". (We of course know that the luminance of a light sample is also an aspect of its color.)

The CIE workers, when devising the XYZ color description model, were able to exercise some of their choices in a very clever way such that the Y "coordinate" of a color is in fact identical to the measure of the luminance of the light.
Yes, luminance is a perceptual property, but like color overall, based on a battery of subjective tests with many human observers, the CIE workers were able to devise an "objective" measure of that property.
This is in fact why "Y" is the mathematical symbol for luminance.

Thus it would seem the combination of the Y and Z coordinates must indicate the chromaticity of the color. Except that they must be interpreted in terms of the luminance. For example, for two colors having the same chromaticity but different luminance, the value of Y differs but the values of X and Z also differ, proportionally.

But we can develop two numbers that do indicate the chromaticity of the light, regardless of its luminance. These are designated x and y. (You might have been expecting x and z!) How handy of we wish to plot chromaticity on a two-dimensional graph!

And it is in fact such a graph, spoken of as a graph of "the CIE x-y chromaticity plane", that, with its iconic horseshoe-shaped boundary, we often see as the base for discussion of many colorimetric matters in terms of the chromaticity of light.

Best regards,

Doug
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Old December 20th, 2017, 01:33 PM
Jerome Marot Jerome Marot is offline
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Quote:
Originally Posted by Doug Kerr View Post
First we determine (perhaps with a spectrophotometer) the power spectral density (PSD) of the light whose color we wish to measure. That is a curve (often called just "the spectrum" of the light) that shows how the power in the light is distributed by wavelength. We can think of it (slightly imprecisely) as a plot of how much power there is in each of the myriad components of the light at its respective wavelength.


It is only fair that I chase you all over the forum with images of black roosters when you use that word, Doug. Don't you think so? It is just an exorcism... 🤡

Eventually, I'll tell you about the cones. I have an interesting observation.
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Old December 20th, 2017, 02:04 PM
Doug Kerr Doug Kerr is offline
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Hi, Jerome.

Quote:
Originally Posted by Jerome Marot View Post


It is only fair that I chase you all over the forum with images of black roosters when you use that word, Doug. Don't you think so? It is just an exorcism... 🤡
Not sure I know what word you mean, but in any case, it seems fair enough.

Quote:
Eventually, I'll tell you about the cones. I have an interesting observation.
Oh, that would be lovely. I prefer the waffle kind, with vanilla in them. Or maybe the orange ones.

In this country, the orange ones have mostly become flattened cones, which stack more densely on the truck.

Then there are the rods. They are different now that surveying depends so much on satellite-based position determining systems. Except for the ones that are a unit of length.

Best regards,

Doug
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Old December 20th, 2017, 02:30 PM
Jerome Marot Jerome Marot is offline
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Not sure I know what word you mean, but in any case, it seems fair enough.
I took the liberty to underline the word in the citation.


Quote:
Originally Posted by Doug Kerr View Post
Oh, that would be lovely. I prefer the waffle kind, with vanilla in them. Or maybe the orange ones.

In this country, the orange ones have mostly become flattened cones, which stack more densely on the truck.

Then there are the rods. They are different now that surveying depends so much on satellite-based position determining systems. Except for the ones that are a unit of length.
I'll let you find out what about the cones, then. I'll give you one word to put you on track: tetrachromat.
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Old December 20th, 2017, 02:42 PM
Doug Kerr Doug Kerr is offline
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Hi, Jerome,

Quote:
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I took the liberty to underline the word in the citation.
Oh, I thought that might have been that. But it's not as interesting word as, say, pyncnometer. Or even psychrometer. Or sling psychrometer.

Quote:
I'll let you find out what about the cones, then. I'll give you one word to put you on track: tetrachromat.
Oh, indeed. Some (very few) humans are, of course. And many non-human animals. (But the discussion here is wholly in the concept of human perception.)

And of course there are humans with four distinct types of cones that are nevertheless not tetrachromatic.

Still, I should consider voting tetrochromat in the next general election.

Best regards,

Doug
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Old December 20th, 2017, 07:47 PM
James Lemon James Lemon is offline
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"To begin at the beginning, one does not measure color. Color is a perceptual quality, and measuring it makes no more sense than measuring poetry. So, when we discuss the measurement of color, we are in fact talking about measuring variation in optical properties such as intensity, reflectance and transmittance over a spectral range – usually the ultraviolet and human-visible portions of the electromagnetic spectrum. Typically, this measurement is performed at a fine wavelength resolution and is called a spectrum (e.g. spectral reflectance, spectral radiance; see Glossary), but there are cases where it is sufficient to measure the variation between a few broad spectral regions. In either situation, the resulting data are often integrated into one of the various models of color vision to create an estimate of color as perceived by humans or other animals (Endler, 1990; Kelber et al., 2003; Endler and Mielke, 2005; Kemp et al., 2015). This Commentary addresses the first part of this process, focusing on the physical act of measuring spectral variation using spectrometers or calibrated photographs"

http://jeb.biologists.org/content/219/6/772
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Old December 20th, 2017, 08:09 PM
Doug Kerr Doug Kerr is offline
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Hi, James,

Quote:
Originally Posted by James Lemon View Post
"To begin at the beginning, one does not measure color. Color is a perceptual quality, and measuring it makes no more sense than measuring poetry. So, when we discuss the measurement of color, we are in fact talking about measuring variation in optical properties such as intensity, reflectance and transmittance over a spectral range – usually the ultraviolet and human-visible portions of the electromagnetic spectrum. Typically, this measurement is performed at a fine wavelength resolution and is called a spectrum (e.g. spectral reflectance, spectral radiance; see Glossary), but there are cases where it is sufficient to measure the variation between a few broad spectral regions. In either situation, the resulting data are often integrated into one of the various models of color vision to create an estimate of color as perceived by humans or other animals (Endler, 1990; Kelber et al., 2003; Endler and Mielke, 2005; Kemp et al., 2015). This Commentary addresses the first part of this process, focusing on the physical act of measuring spectral variation using spectrometers or calibrated photographs"

http://jeb.biologists.org/content/219/6/772
The paper's title tells the story (color emphasis added): "How to measure color using spectrometers and calibrated photographs".

Best regards,

Doug
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Old December 20th, 2017, 08:48 PM
James Lemon James Lemon is offline
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Hi, James,



The paper's title tells the story (color emphasis added): "How to measure color using spectrometers and calibrated photographs".

Best regards,

Doug
Colour is about perception period and they don't measure color.Tone reproduction is the single most important aspect of image
quality. The difference between light and dark.

"In general, unlike mass, volume or temperature, color is not merely a physical property of an object. It is, rather, a sensation triggered by radiation of sufficient intensity. This can be the radiation of a self-emitting light source, or it can be reflected from a surface. This radiation enters the eye, where receptive cells convert it into nervous stimulation, which is in turn transmitted to the appropriate part of the brain, where it is experienced as color. The sensation of color depends not only on physical laws, but also on the physiological processing of the radiation in the sense organs. Visual conditions, luminance (brightness) and the state of the eye’s adaptation are amongst the contributory factors."

https://light-measurement.com/perception-of-color/


James
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Old December 20th, 2017, 10:41 PM
Asher Kelman Asher Kelman is offline
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Quote:
Originally Posted by James Lemon View Post
Colour is about perception period and they don't measure color.Tone reproduction is the single most important aspect of image
quality. The difference between light and dark.

"In general, unlike mass, volume or temperature, color is not merely a physical property of an object. It is, rather, a sensation triggered by radiation of sufficient intensity. This can be the radiation of a self-emitting light source, or it can be reflected from a surface. This radiation enters the eye, where receptive cells convert it into nervous stimulation, which is in turn transmitted to the appropriate part of the brain, where it is experienced as color. The sensation of color depends not only on physical laws, but also on the physiological processing of the radiation in the sense organs. Visual conditions, luminance (brightness) and the state of the eye’s adaptation are amongst the contributory factors."

https://light-measurement.com/perception-of-color/


James
Of course, James, you are entirely correct that "color", outside the use by the rigorous color scientist or process dependent expert steel worker, astrophyicist or chemist), is a merely a qualitative "perception" triggered by various electromagnetic rays of certain energy and wavelength distribution on the mechanisms in the eye and associated visual cortex.

But we are not talking about that homey idea. Instead we are using empirically derived measures of what thousand of humans experience as color and reducing the mathematics of that data set to a rigorous system of look-up tables,

whereby we can predict what perceived color most humans will identify when certain beams are mixed together.

This is indeed highly reproducible physical science. We can say that when you take light beams, (with known chromaticity), p, q and r and combine them, the vast majority of humans will identify the color they perceive as exactly a certain color pqr'

That is good science, the light beams are rigorously defined.

The test of recognition is reproducible in new populations

Now what experience you actually have when you see pqr' is uncertain. My guess is that it is likely the same as mine as we'd both pick the same printed color patch out of thousands choices. But what I see as green you could be seeing as a color that I do not recognize, yet we would still identify the same test patch for the same light mixture. Knowing what I do about biological mechanism and genetics, I feel pretty confident, that if I see and call "lilac", if I could read your mind, you would be having the same perception. I cannot prove that, but it is a reasonable assumption. But colorcscience does not depend on youvand I having thevidentical perception, just that we exactly correlate mixed light beams with the same color patch from myriads of choices.

All we can prove is that we can predict accurately what color patch "everyone ", (as near as matters), would pick to match the color created by mixing the three light beams p, r and q.

Asher
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  #26  
Old December 21st, 2017, 06:36 AM
Doug Kerr Doug Kerr is offline
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Hi, Asher,

Quote:
Originally Posted by Asher Kelman View Post
Of course, James, you are entirely correct that "color", outside the use by the rigorous color scientist or process dependent expert steel worker, astrophyicist or chemist), is a merely a qualitative "perception" triggered by various electromagnetic rays of certain energy and wavelength distribution on the mechanisms in the eye and associated visual cortex.

But we are not talking about that homey idea. Instead we are using empirically derived measures of what thousand of humans experience as color and reducing the mathematics of that data set to a rigorous system of look-up tables,

whereby we can predict what perceived color most humans will identify when certain beams are mixed together.

This is indeed highly reproducible physical science. We can say that when you take light beams, (with known chromaticity), p, q and r and combine them, the vast majority of humans will identify the color they perceive as exactly a certain color pqr'

That is good science, the light beams are rigorously defined.

The test of recognition is reproducible in new populations

Now what experience you actually have when you see pqr' is uncertain. My guess is that it is likely the same as mine as we'd both pick the same printed color patch out of thousands choices. But what I see as green you could be seeing as a color that I do not recognize, yet we would still identify the same test patch for the same light mixture. Knowing what I do about biological mechanism and genetics, I feel pretty confident, that if I see and call "lilac", if I could read your mind, you would be having the same perception. I cannot prove that, but it is a reasonable assumption. But colorcscience does not depend on youvand I having thevidentical perception, just that we exactly correlate mixed light beams with the same color patch from myriads of choices.

All we can prove is that we can predict accurately what color patch "everyone ", (as near as matters), would pick to match the color created by mixing the three light beams p, r and q.
Well said!

Best regards,

Doug
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  #27  
Old December 21st, 2017, 07:20 AM
James Lemon James Lemon is offline
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Quote:
Originally Posted by Asher Kelman View Post
Of course, James, you are entirely correct that "color", outside the use by the rigorous color scientist or process dependent expert steel worker, astrophyicist or chemist), is a merely a qualitative "perception" triggered by various electromagnetic rays of certain energy and wavelength distribution on the mechanisms in the eye and associated visual cortex.

But we are not talking about that homey idea. Instead we are using empirically derived measures of what thousand of humans experience as color and reducing the mathematics of that data set to a rigorous system of look-up tables,

whereby we can predict what perceived color most humans will identify when certain beams are mixed together.

This is indeed highly reproducible physical science. We can say that when you take light beams, (with known chromaticity), p, q and r and combine them, the vast majority of humans will identify the color they perceive as exactly a certain color pqr'

That is good science, the light beams are rigorously defined.

The test of recognition is reproducible in new populations

Now what experience you actually have when you see pqr' is uncertain. My guess is that it is likely the same as mine as we'd both pick the same printed color patch out of thousands choices. But what I see as green you could be seeing as a color that I do not recognize, yet we would still identify the same test patch for the same light mixture. Knowing what I do about biological mechanism and genetics, I feel pretty confident, that if I see and call "lilac", if I could read your mind, you would be having the same perception. I cannot prove that, but it is a reasonable assumption. But colorcscience does not depend on youvand I having thevidentical perception, just that we exactly correlate mixed light beams with the same color patch from myriads of choices.

All we can prove is that we can predict accurately what color patch "everyone ", (as near as matters), would pick to match the color created by mixing the three light beams p, r and q.

Asher
Asher

"In fact, the most popular opinion, at any rate among color scientists, may well be the view that nothing is colored–at least not physical objects in the perceiver's environment, like tomatoes."

http://web.mit.edu/abyrne/www/ColorRealism.html

So getting back to the original question is color a fact or perception?

James
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  #28  
Old December 21st, 2017, 07:25 AM
Doug Kerr Doug Kerr is offline
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I think the underlying dilemma here is that the "color" we measure of an instance of light by objective measurements of the spectral distribution of the light and subsequent mathematical processing, and the "color" that is a sensation of a human viewing that light, are not the same thing.

The "color" we measure, objectively, is a predictor of the "color" that the "average" human viewer would perceive upon viewing that light.

And in fact the process I described earlier really uses a model of the response of the "average" human visual system to light components of different wavelengths. The three "matching curves" I describe are derived from the curves that describe the response of the three kinds of cone receptors in the "average" human visual system.
Well, to be more honest, it works in the other direction. We cannot (very well) measure the response curves of the eye. In fact we infer those curves from the related "matching curves", which are arrived at by empirical testing.
Now would it be more "honest" and "clear" if we did not use the term "color" to refer to the result of this measurement process, reserving that word for the human perception? Sure.

Perhaps we would refer to the result of that measurement as the "protocolor" of the light. Then one could say, "You know, we cannot measure the color of light. All we can measure is its protocolor."

But I did not get the chance to suggest that to the CIE committee that devised the objective definition of "color" and the scheme for determining it. And I would not at all doubt that discussions of that possibility were held. But clearly the decision was to call the defined and measurable metric "color".

And perhaps in my contributions to the discussion here I did not clearly enough illuminate and indicate my recognition that indeed the "color" seen by a human and the "color" measured with an objective process are not the same thing (but we hope they are closely relatable, for the "average" viewer).

This is not the only place in science where we have this duality. Another case is in the "loudness" of sound. That too is a matter of human perception. Yet we use an instrument to measure the acoustic pressure wave arriving at a viewer's location and deliver its finding as the "loudness" of the sound at that point. And, just as in the case of "color", the working of that measurement has "baked in" a model of a certain (somewhat subtle) aspect of human hearing, of course for the "average" listener.

So to answer James' recent question, color (in sense 1) is a fact, and color (in sense 2) is a perception.

Best regards,

Doug
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  #29  
Old December 21st, 2017, 07:47 AM
Doug Kerr Doug Kerr is offline
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It might well have been better for the CIE, in its landmark 1931 work, to have used a word other than "color" for the metric of light they defined. And it might have been desirable, in more modern times, for the CIE to change that term. But in fact it is the term used today for the three-dimensional (in the mathematical sense) metric determined by measurement and analysis of the power spectral density function of an instance of light. So we have a dual meaning for "color", which can be intellectually annoying.

But we cannot "wish that away" by insistence that there is no such thing as the measurement of the color of light, nor such a thing as the color of light at all.

Then there is the wholly different issue of the "color" of a surface, a matter that is far more vexing than that of the color of light.

I'd be glad to speak about that, although that would be very tedious. But that matter is a red herring in a discussion of measurement of the color of light.

Best regards,

Doug
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  #30  
Old December 21st, 2017, 07:54 AM
James Lemon James Lemon is offline
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Quote:
Originally Posted by Doug Kerr View Post
It might well have been better for the CIE, in its landmark 1931 work, to have used a word other than "color" for the metric of light they defined. And it might have been desirable, in more modern times, for the CIE to change that term. But in fact it is the term used today for the three-dimensional (in the mathematical sense) metric determined by measurement and analysis of the power spectral density function of an instance of light. So we have a dual meaning for "color", which can be intellectually annoying.

But we cannot "wish that away" by insistence that there is no such thing as the measurement of the color of light, nor such a thing as the color of light at all.

Then there is the wholly different issue of the "color" of a surface, a matter that is far more vexing than that of the color of light.

I'd be glad to speak about that, although that would be very tedious. But that matter is a red herring in a discussion of measurement of the color of light.

Best regards,

Doug
Doug

Radiation can be measured but light and color is a subjective human sensation and therefore can not be measured.

James
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