I On Mixing Colors of Light

[sophiecentaur]

but it wasn’t a good medium.

The darkroom safe light was always over-optimistic. The image on paper would gradually come into view and it would look so promising. Total magic. You took it out of the Dev dish and dumped it in the Fix dish; safe to turn on the room lights. Nearly always, the result was tired, soft and low contrast but no chance to click the history button and start again.
Someone will point out that you need to be much better disciplined. True; the thermometer and timer should always rule.

 

[DaveC426913]

Nearly always, the result was tired, soft and low contrast but no chance to click the history button and start again.

Huh. Describes my high school experience exactly.

 

[Calstiel]

All three sets of cones have overlapping spectral sensitivity over more or less the whole spectrum. Without that, the eye would be blind to awkwardly placed and "narrow band" colours. This is why the three analysis curves are not described as Red Green and Blue but L,M and S . The diagram shows those curcespresented with 'spinach'.

Can you give me the name from the paper from this diagram?

 

[sophiecentaur]

Can you give me the name from the paper from this diagram?

Here is the link. Many others are available

 

[Charles Link]

See https://en.wikipedia.org/wiki/CIE_1931_color_space
There seems to be an open item on the LMS (long, medium, short) and the X,Y, Z response curves where there is a clear discrepancy between these two. I have limited search resources on why these two are so different, but they are. I tend to believe that the X,Y, and Z is more accurate.

 

[sophiecentaur]

The goal is to generate a perceptually accurate yellow

That is a very limited goal. It's not a good basis for spectrometer design. CIE were in the business of good colour reproduction and a two colour system is not sufficient. I cannot understand why Yellow seems to be taking up most of the comments on this thread. Making Yellow with a green and a red light is great for a reliable demonstration with crude equipment in school but not a lot else.

 

[Charles Link]

The concept here is more detailed, and to try to show why the primary colors are what they are. I found it very interesting that there is a spectral yellow from 580-590 nm, and alo a perceived one, made from green at 550 nm and red at 650 nm or thereabouts. With the mixing of light explained, and that with red and green, they do not physically make any 580-590 nm,= this to me is important.

Then there is the other part=why is yellow then a primary color in mixing paints? I thought @sophiecentaur and others did a very good job of answering that in the thread, why do yellow and blue light not make green light?, in the thread that was linked far above, which I will find again momentarily. Yes, see https://www.physicsforums.com/threads/color-theory-what-does-blue-yellow-make.1008903/

 

[Charles Link]

Just a comment or two: We really need to be willing to discuss fundamentals at times, how boring it may be to some, even things as basic as the Pythagorean theorem or the quadratic formula, or soon we will have a generation where nobody (of the younger generation) knows how to do anything any more. If their cell-phone doesn't give them the answer, they will be all thumbs, and it would be far better to have a generation that know much of the fundamentals once again.

 

[sophiecentaur]

do yellow and blue light not make green light?,

Yellow is not a primary colour in the additive world. To put yellow into the additive world you call it -B (minus B); it's what you get when you take blue away from white. Pigments and filters subtract appropriate wavelengths.
If you draw a line from the yellow spot to the blue primary spot, the resultant will pass from yellow to blue and go through a de-saturated bluey-green area. (always inside the triangle of primaries). Unfortunately (for image processing people) we all get taught in primary school about mixing paints but primary school teachers can't be expected to use the word 'caveat'. If the thread strays into subtractive mixing, I will get my hat and coat.

 

[Charles Link]

Yellow is not a primary colour in the additive world. To put yellow into the additive world you call it -B (minus B); it's what you get when you take blue away from white. Pigments and filters subtract appropriate wavelengths.
If you draw a line from the yellow spot to the blue primary spot, the resultant will pass from yellow to blue and go through a de-saturated bluey-green area. (always inside the triangle of primaries). Unfortunately (for image processing people) we all get taught in primary school about mixing paints but primary school teachers can't be expected to use the word 'caveat'. If the thread strays into subtractive mixing, I will get my hat and coat.

Subtractive mixing is the last thing I would want to see as well. One thing that I think could use some clarification, (and this has come up), is that the complete human perception that can be viewed is all from colors/wavelengths that lie on the outer edge of the tongue that is the CIE color map. You can go to the interior part of that region and get a color, but that color is simply a combination of other wavelengths/colors from the fringe, and a little study, not even a large study, shows that the composition that makes up the color in the interior is not at all unique. That's where, once again, the spectral wavelength view of things is really much more fundamental than the CIE chart.

 

[berkeman]

Thread is closed for Moderation...

 

[berkeman]

After removing a likely AI-assisted side conversation by a problematic member, this thread is now reopened. Thanks for your patience.

 

[sophiecentaur]

After removing a likely AI-assisted side conversation by a problematic member, this thread is now reopened. Thanks for your patience.

Scary stuff.

 

[Charles Link]

When you've got someone (@Crispybacon) who tells you you've got a good idea or two, and then you find out some of that opinion may have been formulated by a robot. I'm skeptical=I think this one may have been human, even if he did use artificial intelligence to help him write some of his inputs.

 

[DaveC426913]

When you've got someone who tells you you've got a good idea or two, and then you find out some of that opinion may have been formulated by a robot. I'm skeptical=I think this one may have been human, even if he did use artificial intelligence to help him write some of his inputs.

PF has a policy of not allowing AI-generated content. That's not to say one cannot use AI bots to help one's writing, but it is required that it be the human's words, not the words an AI merely barfed-up.

Further discussion should probably move to the Feedback section.

 

[Charles Link]

PF has a policy of not allowing AI-generated content. That's not to say one cannot use AI bots to help one's writing, but it is required that it be the human's words, not the words an AI merely barfed-up.

I remain skeptical. It was the best feedback I have gotten in the last two months, and I find it hard to believe that the robots can actually appear as intelligent as some of us. He liked my OP=he actually said he "loved" it=to date I think it has only gotten 2 "likes".

 

[DesertDog1830]

I want to reiterate something that for me was a major find with the CIE chart that I mentioned in posts 23 and 24 above. It basically treats the 3 color bands [Edit=color cone stimulus/response] in 3 dimensions with the X, Y, and Z being the intensity of each band. (X=red cone, Y=green cone, Z=blue cone). The light of a given luminance and color is a vector $\vec{R}=X \hat{i}+Y \hat{j}+ Z \hat{k}$ , and where the line $\vec{R} t$ crosses the plane $x+y+z=1$ is designated as the color coordinate. The CIE chart is a color map in this plane which crosses the axes at $(1,0,0)$, $(0,1,0)$ , and $(0,0,1)$. (They usually show it as an x-y graph, but they are actually showing the view from above of the map in the plane $x+y+z=1$.)

If you have two sources of some intensity with different color coordinates on this chart, making vectors of two different lengths, the resultant vector will be in the plane containing these two vectors, and its color coordinates are found by where the line made from this resultant vector passes through the plane $x+y+z=1$. The CIE chart is really a neat piece of mathematics. See also https://en.wikipedia.org/wiki/CIE_1931_color_space , but they don't seem to highlight these details.

Edit: It should be noted that the vector $\vec{R}$ above thereby has color coordinates of $x=X/(X+Y+Z)$, $y=Y/(X+Y+Z)$ , and $z=Z/(X+Y+Z)$.

Good!

 

[Charles Link]

To add a couple additional comments to post 160 above, it might be worth mentioning that the CIE diagram puts the visible spectrum simply on the edge of the tongue-shaped color map, essentially on a line/curve that has zero area. These spectral colors on the fringe are still the much more fundamental item here than the entire color space in the interior of the color map, which can be created from spectral sources on the fringe of the diagram. In fact it should be stated that any color light source is a combination of spectral sources from the fringe=perhaps I'm stating the obvious, but it might be worth mentioning.

One other item worth mentioning is that the spectral composition of any location in the interior of the CIE color map is not unique. Instead many, many different spectra can have the same color coordinates. Even a little arithmetic with the CIE color coordinates on the upper right section of the color coordinates map suggests that you can even generate colors on the fringe of the color map from pairs of adjacent spectral colors on the fringe. (e.g. red and green in the right combination can give yellow or orange). For the section on the upper right fringe, there is essentially no excitation of the blue cone, i.e. $z \approx 0$, because $x+y+z=1$, and in this case $x+y \approx 1.0$.

To reiterate what was mentioned in the OP, mixing these colors does not change their spectral composition, again something that may be obvious to some, but probably not to everyone. If the light is originally composed of red and green light, after mixing it is still simply composed of red and green, regardless of how it appears to the eye.

Hoping at least a couple of people find this useful reading. So far, the feedback has been rather limited, so it's difficult to assess whether anyone is finding this useful.

 

[Charles Link]

Just one additional comment: If it is going to be credible physics, I do have to give posts such as @sophiecentaur 's of post 146 much consideration. I am not infallible, but on this one I stick to what I have put forward in the OP. The CIE color chart also supports the concept of the OP=it is possible that is also an approximation and it certainly isn't a perfect model, (assumes linear responses of the color cones that can be added as vectors).

Note: I looked through a number of @sophiecentaur 's previous posts over the last 6 months, and there is no doubt that his physics is first rate, but on this item, I think I offer the better explanation. The concept in my OP is based on mainstream physics, but even the brightest ones don't always agree on everything. Everyone is entitled to their opinion. I do try to keep an open mind to others who don't agree with any physics that I promote, but on this one, I stick with my OP for better or worse. Cheers. :)

 

[sophiecentaur]

: If it is going to be credible physics,

But how much actual physics is involved here? The reason that the system works is human psychology. The Physics at work is as varied as the different technologies involved. You have repeated your view many times in this thread. I have just been saying standard chapter and verse on the topic. Can you quote any creditable source to justify what you have been saying?

 

[Charles Link]

Can you quote any creditable source to justify what you have been saying?

I am retired. I don't presently have access to much of the literature. You are welcome yourself though to do the calculation with the CIE color map that you presented early-on in post 16. Most of the upper right hand border ( the spectral fringe) lies very near the line $x+y=1$, with the result that $z=0$ for those spectral sources to a very good approximation. The result then is that the green at 550 nm and the red at 650 nm together in the right combination can generate something that looks almost exactly like something at 580-590 nm.

I really never intended to generate any controversy here=I really thought the OP might pick up a few likes and most might find it interesting and maybe even agree with it. It is also still a possibility that the CIE chart isn't entirely accurate. I don't know whether anyone has conducted a similar experiment like I proposed in the OP. Perhaps the human subjects would be able to tell a slight difference. That remains an open item.

Edit: and the human subject part of it, i.e. what the human perceives, I would categorize as biophysics or opthalmology, rather than psychology.

 

[sophiecentaur]

I don't know whether anyone has conducted a similar experiment like I proposed in the OP.

I seem to remember seeing an arrangement of prisms and slits in a work by Isaak Newton. He already sussed out the difference between 'colour' and 'spectrum' and he demonstrated how you can synthesise white light by adding colours. He didn't have the advantage of a handy CIE diagram, of course but what 'new' stuff is proposed here?

Edit: and the human subject part of it I would categorize as biophysics or opthalmology, rather than psychology.

A rose is a rose is a rose. I would say that Physics does not involve subjective testing or at least it tries to eliminate the human element when possible.

 

[Charles Link]

He didn't have the advantage of a handy CIE diagram, of course but what 'new' stuff is proposed here?

Probably nothing terribly new, but we do know about light as having wavelengths, something that Newton did not have in his time.

On a plus note, thank you for introducing the CIE color chart in post 16. If this thread served no other purpose, I did learn about how the CIE color chart works. Cheers. :)

 

[Charles Link]

and a follow-on: Basically I think I may have reinvented the wheel in the OP. The mixing of a colors of light might have been something kind of new about a hundred years ago, but today's technology with the flat TV screens with microscopic size pixels has advanced far beyond anything I presented. In any case, I still find the fundamentals of interest, and they do make for good discussion.

The same sort of thing applies to things like our cell phone technology. How they ever are able to manufacture things like the cell phones as well as memory cards and mass produce them is totally beyond me=it is possible that the science has advanced beyond what can be readily understood by most, but I still think it is worthwhile for students to know about things such as photodiodes and LED's (light emitting diodes). The best science IMO is of concepts that most can understand. The ideas might have been a little simplistic, but hopefully at least a couple of readers found the above thread of interest.

 

[sophiecentaur]

I don't know whether anyone has conducted a similar experiment like I proposed in the OP.

I seem to remember seeing an arrangement of prisms and slits in a work by Isaak Newton. He already sussed out the difference between 'colour' and 'spectrum'. It's certainly not new.

 

[Charles Link]

I seem to remember seeing an arrangement of prisms and slits in a work by Isaak Newton. He already sussed out the difference between 'colour' and 'spectrum'. It's certainly not new.

The idea I put forward in the OP two months ago was new to me, (perhaps not to you), but it has now gotten a little old. Right now it would interest me if someone could explain how they can make and mass produce several million or more p-n junctions (photodiodes) in a very tiny space, all with electrical connections, or how they can manufacture a billion or more memory cells on a small memory card, but that would be the subject of another thread.

Edit: The ideas in the OP may be a little simple, but they are more my speed. Science and technology has advanced so much in the last 20 or 30 years=perhaps even beyond our intelligence.

Edit 2: Just an additional comment or two=for those who already know all about the red, green, and blue color cone sensors of the human eye along with the CIE color map, that the original post=the OP might seem very simple, but for me I thought it to be good physics, and I still think they would do well to address the subject of the mixing of colors of light in the undergraduate physics curriculum=perhaps as part of the Optics course.

 

[Charles Link]

I just did a little googling on the subject of red, green, and blue color cones and came up with the following:
See https://en.wikipedia.org/wiki/Young–Helmholtz_theory

It looks like @sophiecentaur indeed has it correct, that the original post=the OP, presented nothing new= Thomas Young came up with a good part of this, and others have added to it since then.

If the mixing of colors of light along with the perception of the human eye is not taught as part of the standard curriculum, it seems it will be something that some may know very well, while others may be left with little or no expertise in that area. In any case, IMO this wiki article is a good one and others may find it of interest as well.

New or not though, I still think the OP that I posted is reasonably good physics. Even though I did a lot of work with diffraction grating spectrometers, mixing colors of light was a new topic for me, and one that I found very interesting.

 

[AlexB23]

TL;DR Summary: Doing a discussion with a Gedanken experiment of mixing green (550 nm) and red light (650 nm) and comparing it to that of yellow light at 600 nm

I want to illustrate what the color mixing that is done with a tv screen is all about, and how we can generate the appearance of color using primary colors, even though we don't actually generate any light of the color that we perceive. Consider beginning with a tungsten filament with a current running through it that creates a continuous spectrum that can be approximated by a T= 2500 K blackbody for a typical case where it generates white light.
Let's have that light be collimated by a lens and run it through a prism=basically a prism spectrometer that will split the visible light into the colors of the rainbow, because the index of refraction of the glass of the prism decreases with increasing wavelength.

Now let's sample the output at the locations where the spectrum is green (550 nm) and red (650 nm) and combine these with the necessary mirrors and or lenses onto a sheet of white paper. If we get the proportions right, we should observe some yellow light.

We can also sample the output of the prism at the angle about midway between where the green and red emerge, and there we will find yellow light at 600 nm. If we focus this onto a white sheet of paper, it is likely we can not tell the difference with our eyes between this and the green and red combination.

The next part is to send some of the yellow light that comes off the white paper into a second prism spectrometer. In the first case, we will find green and red light to emerge in the same proportion that we started with at the angles corresponding to 550 nm and 650 nm, but nothing at the 600 nm location. In the second case, everything will emerge at the 600 nm location. The light that is made of green and red light appears yellow, but the light doesn't change its composition when the green is combined with the red. It is still a mixture of green and red, even though it appears yellow.

Thought you might find this of interest. I welcome your feedback. I just came up with this the other day. Generally I don't think they treat this topic in very many of the textbooks in the manner in which I presented above.

Would the 650 nm light + 550 nm light appear yellow, as it would average out to 600 nm? I am not that good at optics.

 

[sophiecentaur]

Would the 650 nm light + 550 nm light appear yellow, as it would average out to 600 nm? I am not that good at optics.

Don't worry about your optics. Colourimetry is way outside mainstream optics; it's mainly to do with how the sensors in your eye work and how the brain recognises the result of mixtures of wavelengths and maps it onto 'colour space'.

When you say "average out" that would only be right for 'equal' levels of the two primaries you have selected. Controlling the levels of those two independently can produce a colour that looks the same as (a metemer) an approximate spectral colour. That colour will lie on a straight line between the two primariesUse the formulae in some of the posts higher up this post. Of course, the really interesting bit is how three primaries, in the appropriate relative levels can produce a 'match' of any colour within the triangle (nowhere near the spectral curve).

Imo it is risky to use the words 'colour' and wavelength together without being very aware that they are actually different things. Colour is what your brain makes of a range of different colours which only 'might' be monochromatic (spectral lines) Most of the colours we see are not from monochromatic sources. It is sad that so many 'experts' misuse the two terms. How can anyone be expected to get understanding of this topic in this desert of colourimetric misinformation?

 

[hutchphd]

(a metemer)

Metamer is how I learned to spell it
Wikipedia also does a pretty good explanation (graphs and all!)

 

[pinball1970]

Metamer is how I learned to spell it
Wikipedia also does a pretty good explanation (graphs and all!)

And metamerism in the phenomena. Trying to explain the difference between colour constancy and metamerism has been something of a feature at work for a while.

 

[pinball1970]

Metamer is how I learned to spell it
Wikipedia also does a pretty good explanation (graphs and all!)

And metamerism in the phenomena. Trying to explain the difference between colour constancy and metamerism has been something of a feature at work for a while.

 

[sophiecentaur]

colour constancy

Never heard of of that one. I guess it means how much difference in the RGB values is noticeable(?). I remember the JND (just noticeable difference) which is different in various regions of the CIE diagram.

 

[pinball1970]

Never heard of of that one. I guess it means how much difference in the RGB values is noticeable(?). I remember the JND (just noticeable difference) which is different in various regions of the CIE diagram.

We use it for assessment of samples under different lights. Clients have different requirements and point of sale.
In short if they want a particular colour, they want that colour not to be different depending on where that setting is.
It presents a lot of challenges, as an example, say a car has interior grey, upholstery, seat belt and an exterior that matches.
Requirement is the car looks that colour in the show room and when it out in daylight.
The showroom will have a particular SPD and daylight has a different one.

 

[sophiecentaur]

Paints and pigments are a real pain. TV engineering is a piece of cake in comparison.

 

[pinball1970]

Paints and pigments are a real pain. TV engineering is a piece of cake in comparison.

Yes, three different sets of colourants for metal, leather and upholstery.
My old lab dealt with the interior side in the 90s so metamerism and colour constancy was a major part.

Life is simpler these days, but I miss it!

 

[AlexB23]

Don't worry about your optics. Colourimetry is way outside mainstream optics; it's mainly to do with how the sensors in your eye work and how the brain recognises the result of mixtures of wavelengths and maps it onto 'colour space'.

When you say "average out" that would only be right for 'equal' levels of the two primaries you have selected. Controlling the levels of those two independently can produce a colour that looks the same as (a metemer) an approximate spectral colour. That colour will lie on a straight line between the two primariesUse the formulae in some of the posts higher up this post. Of course, the really interesting bit is how three primaries, in the appropriate relative levels can produce a 'match' of any colour within the triangle (nowhere near the spectral curve).

Imo it is risky to use the words 'colour' and wavelength together without being very aware that they are actually different things. Colour is what your brain makes of a range of different colours which only 'might' be monochromatic (spectral lines) Most of the colours we see are not from monochromatic sources. It is sad that so many 'experts' misuse the two terms. How can anyone be expected to get understanding of this topic in this desert of colourimetric misinformation?

Fascinating stuff. I do agree, as colorimetric stuff is not optics. Yeah, a lot of people including myself conflate color with wavelength or frequency, when color is just how we perceive these light waves.

 

[blue raven]

What does that mean? As you move between areas on the CIE chart, why shouldn't more than one value change?

Did you notice that there are very few objects in a scene with one of RGB being near zero? Saturated colours are rare in everyday scenes.

In the real world, when we made a change to one color, actually the other colors are affected as well by this change, but not in the same manner. Imagine we have sliders (values) for each color, and when you move one slider, the other sliders (values) will also start to move/change. So in the real world it is impossible to change just one color. For example, if you want to make a color redder, by adding red the green will be strongly affected, the violet will be a bit affected, the only one that won't be affected is the black, which has a kind of color inertia. When you look at such color charts, if you think you can move on one axis, in reality you can't, and you will move on two or more axes, creating a bit of a mess.

@Charles Link
I think the CIE graph has one big hole, namely the lack of black (or perhaps "darkness"? ) that appears in CIE Lab space as negative L, which reduces virtually any color, see this relatively accurate representation (others are not so good)

Why black (color) matters? Because using white and black you can produce 3D effects (and this might be quite interesting for physics, even thinking about black holes) and without black it does not work very well.
So many posts, and you haven't even scratched the surface of this interesting topic. You should be bolder.

 

[Charles Link]

@blue raven The Physics Forums rules only allow for mainstream physics, and do not allow for any personal theories where we are creating things that are outside of the realm of what has been established as credible science.

 

[sophiecentaur]

In the real world, when we made a change to one color, actually the other colors are affected as well

I think you need to re-think this. You would need to specify which part of the 'real world' you are discussing. Are you talking in terms of Analysis or Synthesis?

Synthesis: It's easy to vary the R primary signal to the display without changing the G and B primary voltages and you would get a result that lies along a line between the white point and one side of the triangle.

Analysis: It would be very difficult to change the pigment / paint / filter to change just one of the tristimulus values.

namely the lack of black

Your worry is misplaced. The whole point of the CIE (chrominance)chart is that it is independent of the Luminance. I mentioned earlier that 'skin tones' are virtually identical for pale skinned Nordics and very dark skinned Africans. The RGB signals have more or less the same ratios for both skins. You can have a lot of fun with a colour picker, writing down the RGB values for various faces in a crowd.

If you look at the old PAL / NTSC coding you see the levels of luminance , varying over each tv line andthe phase carrying a high frequency chrominance subcarrier signal which varies in amplitude (saturation) and

'hue (the phase of the subcarrier). This colour bar signal uses very saturated bars.

 

[blue raven]

@blue raven The Physics Forums rules only allow for mainstream physics, and do not allow for any personal theories where we are creating things that are outside of the realm of what has been established as credible science.

I don't recall such a topic "Mixing light colors" in theoretical physics, but in 2014 the Nobel Prize in Physics was awarded for the invention of the blue LED, and there you might find some related topics that can be explored without being accused of drifting apart from mainstream physics, such as how a photon is produced, the energy of a photon in quantum mechanics, valence, conduction and gap bands, see this video


You might find also interesting the topic about fluorescent and phosphorescent colors
https://en.wikipedia.org/wiki/Luminous_paint

 

[sophiecentaur]

I don't recall such a topic "Mixing light colors" in theoretical physics

Colourimetry is not 'theoretical' it's to do with very much applied Physics.

accused of drifting apart from mainstream physics

Who would be 'accusing' anyone? PF has a foot in all fields.

 

[hutchphd]

The "physics" of colorimetry is rather straightforward. The eyes report the "color" based upon the integrated intensity from several differently sensitive chromophors in the eye. (Note that this depends upon both the illuminant and the object under study, thus allowing metamerism) The assignment of color to an object is not therefore unique. In addition the reduction of a spectrum to a handfull of data is very "lossy". These are "known unknowns".
In addition there are a host of "physiologic" unknowns that have to do with processing this data into what we call "color". Many of these are "unknown unknowns".( https://en.wikipedia.org/wiki/There_are_unknown_unknowns)
But it represents a relatively arcane corner of physics (which paid my bills for quite a span)

 

[blue raven]

Synthesis: It's easy to vary the R primary signal to the display without changing the G and B primary voltages and you would get a result that lies along a line between the white point and one side of the triangle.

Analysis: It would be very difficult to change the pigment / paint / filter to change just one of the tristimulus values.

If you look at the old PAL / NTSC coding you see the levels of luminance , varying over each tv line andthe phase carrying a high frequency chrominance subcarrier signal which varies in amplitude (saturation) and

'hue (the phase of the subcarrier). This colour bar signal uses very saturated bars.View attachment 355873View attachment 355874

And have you wondered how accurate these colors were reproduced on the screen? Back in time, it was common knowledge that screens didn't accurately reproduce colors to match a quality print. There was quite a difference between the image on the screen and the print.
Any change at the input must be measured at the output, using a device such as a spectrophotometer like this one, X-rite i1 or cheaper ones. Nowadays, good monitors can be calibrated in the range of an acceptable error Delta E, where this error is given by the deviations from the target color on the color map/space, see what Delta E is. A calibrated monitor comes with a report that shows the values of this Delta E error for each color, if I remember correctly. So the challenge is to keep all errors below Delta E<1.5, this error is good, in this case you can be sure that all colors displayed on the screen will match a quality print, which also can be verified using a spectrophotometer.

 

[pinball1970]

And have you wondered how accurate these colors were reproduced on the screen? Back in time, it was common knowledge that screens didn't accurately reproduce colors to match a quality print. There was quite a difference between the image on the screen and the print.
Any change at the input must be measured at the output, using a device such as a spectrophotometer like this one, X-rite i1 or cheaper ones. Nowadays, good monitors can be calibrated in the range of an acceptable error Delta E, where this error is given by the deviations from the target color on the color map/space, see what Delta E is. A calibrated monitor comes with a report that shows the values of this Delta E error for each color, if I remember correctly. So the challenge is to keep all errors below Delta E<1.5, this error is good, in this case you can be sure that all colors displayed on the screen will match a quality print, which also can be verified using a spectrophotometer.

1.5 is huge EDIT: Big

 

[Charles Link]

@blue raven The video in post 191 is interesting, but there is a big step I am missing that I mentioned also in post 176=how do we go from having just one of these blue LED's to suddenly being able to manufacture millions of them on a computer screen? There seems to be some way of copying things atom by atom that was never taught in the classroom to students of my generation. That is in a way getting off topic, but at the same time it is relevant to this topic and would bring it up to date to how things are presently being done.

 

[sophiecentaur]

Back in time, it was common knowledge that screens didn't accurately reproduce colors to match a quality print.

It's an on-going problem I think. A "quality " print is a bit of an oxymoron. A printed image of a familiar object (or have the object and print side by side) will often be a disappointment and that's even when not through a TV. I have used the word "illuminant" frequently in this thread and it's essential to include the lighting in reliable colour matching. Most quality prints on people's walls have to take what they get in the way of room lighting.
Colour films seen in the cinema had dreadful colour fidelity. But they used to get away with it because cinema lights were switched off for viewing so your eye had nothing to judge the colour against except the 'integrates to grey' of the whole scene. And people were a lot less fussy than when sitting in their home with some lights on, watching TV. Nowadays, the owner of a $1k tv will never criticise what they paid that money for.

 

[sophiecentaur]

That is in a way getting off topic,

It certainly is. lol. Why not start a new thread? I can see you have already found a Google page for information.

 

[sophiecentaur]

all colors displayed on the screen will match a quality print,

You are comparing apples with oranges here. A "quality print" will have the benefit of human intervention and a choice of many pigments; it's a one off. A TV / camera system has to deal with everything that's thrown at it, once the illuminant has been added into the mix.

However many times it's mentioned that Colour is not Wavelength there seems to be a background routine in people's minds that rejects that idea. Primaries - whether pigments or phosphors- are colours; each manufacturer can use any spectra to produce a given 'colour' of primary. Two layers of 'primary' filters can produce black (if there is no overlap in responses) or something like the primary colour that sits between them. Colour wheel diagrams seem to ignore this entirely. Printed results can be exquisite but it all a depends on skill and experience of the expert printer (person).

The rot starts to set in at Primary School in Art classes. But. hell, teacher training can't have a colourimetry class squeezed into the teaching course curiculum.

 

[.Scott]

It's always risky to pipe in this late in a discussion. But I think that there are two items that have not been covered.
First, when color/intensity comparisons are done, they are most precise when the two samples adjoin each other. So, in the original experiment, I suggest that the both the pure tone color and the two-tone metamer be projected side by side with a hard transition between them - and with mechanisms to adjust the brightness of all three tones so that a very close match can be perceived. It would then be interesting to make comparisons among several observers - perhaps we would find "metamer twins".

The other issue is relates to color perception. It isn't just the "pixel readout" of the rods and cones that makes the color. Edges detected in the visual field by the brain are categorized as either "illumination edges" or "reflection edges". Illumination edges are caused by changes in those "pixel values" across the visual field due to differences in the lighting and orientation of the subjects being viewed. So, for example, if you are looking at a red car on a sunny day, the actual "pixel values" across the car will be different depending on whether they are facing the sun, directly reflecting the suns image, or in a shaded spot. But, as long as we recognize that all of those changes are due to illumination, we will see only a single color.

A better example is looking at the same object in ambient lighting with different color tints. To the extent possible, the brain will attempt to compensate. Of course, there are limits. If you look at a parking lot illuminated only by Sodium or Xenon lighting, you'll likely notice that some car colors are missing from the lot.

There were a lot of these kind of experiments in the 1980s. (Sorry for the lack of citations. I don't have access to that kind of library here). One experiment is to look through a tube (like a cardboard paper towel tube) at one spot in the visual field - so that the brain doesn't have enough context to recognize illumination factors. So, for example, looking through a blue-tinted bottle without the tube allows you to correctly ID colors. But looking through the tube at the same spot forces you into "pixel" mode.