Obviously, this "debate" is more-or-less over, as you are doing nothing but spoiling for a fight.

DavidMcC wrote:
I don't "prefer" to call a yellow square "yellow", I just think it is appropriate when the pixels in it are not resolved (unless you use a magnifying glass), so that green and red areas merge to yellow, so that the avearge physicakl colour is yellow.

And you wanted to make a distinction between perceptual and physical colour? All you are saying here is that you want to call it yellow because you aren't looking at the details and it looks yellow to you. Your reply acknowledges that the photons have wavelengths we would perceive as red and green. If the photons aren't the "physical colour" WTF is?

I will credit you with knowing that mixing "red photons" and "green photons" doesn't create "yellow photons".

GrahamH wrote:

DavidMcC wrote:
I don't "prefer" to call a yellow square "yellow", I just think it is appropriate when the pixels in it are not resolved (unless you use a magnifying glass), so that green and red areas merge to yellow, so that the avearge physicakl colour is yellow.

And you wanted to make a distinction between perceptual and physical colour? All you are saying here is that you want to call it yellow because you aren't looking at the details and it looks yellow to you. Your reply acknowledges that the photons have wavelengths we would perceive as red and green. If the photons aren't the "physical colour" WTF is?

I will credit you with knowing that mixing "red photons" and "green photons" doesn't create "yellow photons".

If you do some wavelength arithmetic, they would average to yellow photons, doesn't that count?

scott1328 wrote:

GrahamH wrote:

DavidMcC wrote:
I don't "prefer" to call a yellow square "yellow", I just think it is appropriate when the pixels in it are not resolved (unless you use a magnifying glass), so that green and red areas merge to yellow, so that the avearge physicakl colour is yellow.

And you wanted to make a distinction between perceptual and physical colour? All you are saying here is that you want to call it yellow because you aren't looking at the details and it looks yellow to you. Your reply acknowledges that the photons have wavelengths we would perceive as red and green. If the photons aren't the "physical colour" WTF is?

I will credit you with knowing that mixing "red photons" and "green photons" doesn't create "yellow photons".

If you do some wavelength arithmetic, they would average to yellow photons, doesn't that count?

There would be no yellow photons present. All that counts for perceiving yellow is to have similar excitation of L and M cones and negligible stimulation of S cones, which could result from all sorts of spectra.

GrahamH wrote:

scott1328 wrote:

GrahamH wrote:

DavidMcC wrote:
I don't "prefer" to call a yellow square "yellow", I just think it is appropriate when the pixels in it are not resolved (unless you use a magnifying glass), so that green and red areas merge to yellow, so that the avearge physicakl colour is yellow.

And you wanted to make a distinction between perceptual and physical colour? All you are saying here is that you want to call it yellow because you aren't looking at the details and it looks yellow to you. Your reply acknowledges that the photons have wavelengths we would perceive as red and green. If the photons aren't the "physical colour" WTF is?

I will credit you with knowing that mixing "red photons" and "green photons" doesn't create "yellow photons".

If you do some wavelength arithmetic, they would average to yellow photons, doesn't that count?

There would be no yellow photons present. All that counts for perceiving yellow is to have similar excitation of L and M cones and negligible stimulation of S cones, which could result from all sorts of spectra.

Actually, I was being facetious in my comment, but upon second reading, i can see that my poor attempt at humor was lost.

DavidMcC wrote:
You and Graham seem to be making much of your ignorance of colour displays

Well whatever ignorance I may possess ... at least I did not claim nuclear decay is zero order. And when having your nose rubbed in it you claim it is isn't logical nomenclature when it actually it is.

David, what would you say about the 'physical colours' of the arrowed squares?

Maybe we could call that physical colour 130R 70G 15B and the perceptual colour might be brown or orange, or something else...

GrahamH wrote:

scott1328 wrote:

GrahamH wrote:

DavidMcC wrote:
I don't "prefer" to call a yellow square "yellow", I just think it is appropriate when the pixels in it are not resolved (unless you use a magnifying glass), so that green and red areas merge to yellow, so that the avearge physicakl colour is yellow.

And you wanted to make a distinction between perceptual and physical colour? All you are saying here is that you want to call it yellow because you aren't looking at the details and it looks yellow to you. Your reply acknowledges that the photons have wavelengths we would perceive as red and green. If the photons aren't the "physical colour" WTF is?

Even when there are only photons of "yellow" wavelength, they are only perceived (normally) as yellow because they excite the MW and LW cone cells roughly equally. This can also be achieved by a fine mixture of rd and green. (NB, Forget animals with completely different colour vision - they are irrelevant, even from the POV of the names of physical colours.

I will credit you with knowing that mixing "red photons" and "green photons" doesn't create "yellow photons".

If you do some wavelength arithmetic, they would average to yellow photons, doesn't that count?

There would be no yellow photons present. All that counts for perceiving yellow is to have similar excitation of L and M cones and negligible stimulation of S cones, which could result from all sorts of spectra.

... The different appearance of the different "yellow" squares in the pictue of the cube is actually a distortion of shade perception due to the strong proximity effect of shade - one has a darker appearance than the other, but appear to have approximately the same hue. This effect helps extend edge visibility over a wider range of brightness than otherwise. Thus, it probably evolved to help with predator detection.

EDIT: Thus, some kinds of brown can look yellow if they are surrounded by even darker shades.

BTW, re yesterday's spat over my wording for the description of the "yellowish" square: I was trying to generalise, but I admit that it came out sounding rather abstruse. To clarify, by "local microcolour", I meant the RGB co-ordinates of the individual pixel (or rather, sub-pixel) elements. As it is part of an emissive display, these would represent the actual brightness of light entering the eye, rather than any reflectivity colour.

DavidMcC wrote:... The different appearance of the different "yellow" squares..

...is an appearance (i.e. "perceptual colour")

GrahamH wrote:

DavidMcC wrote:... The different appearance of the different "yellow" squares..

...is an appearance (i.e. "perceptual colour")

Acually, it's more a matter of shade than hue. The "brown" and "yelllow" squares do not look like very different hues, just very diffeent shades.
I suppose you can define "colour" as including shade as well as hue.

DavidMcC wrote:

GrahamH wrote:

DavidMcC wrote:... The different appearance of the different "yellow" squares..

...is an appearance (i.e. "perceptual colour")

Acually, it's more a matter of shade than hue. The "brown" and "yelllow" squares do not look like very different hues, just very diffeent shades.
I suppose you can define "colour" as including shade as well as hue.

I think that having a different name for a colour is sufficient difference.

What do you say about the "physical colour" of those squares? Is there one colour, or two (brown and yellow?) to match the "perceptual colours"?

GrahamH wrote:

DavidMcC wrote:

GrahamH wrote:

DavidMcC wrote:... The different appearance of the different "yellow" squares..

...is an appearance (i.e. "perceptual colour")

Acually, it's more a matter of shade than hue. The "brown" and "yelllow" squares do not look like very different hues, just very diffeent shades.
I suppose you can define "colour" as including shade as well as hue.

I think that having a different name for a colour is sufficient difference.

What do you say about the "physical colour" of those squares? Is there one colour, or two (brown and yellow?) to match the "perceptual colours"?

Definitely only one physical colour, but two perceptual colours, based on post-processing of cone cell signals in some part or other of the visual cortex.

DavidMcC wrote:

GrahamH wrote:

DavidMcC wrote:

GrahamH wrote:

...is an appearance (i.e. "perceptual colour")

Acually, it's more a matter of shade than hue. The "brown" and "yelllow" squares do not look like very different hues, just very diffeent shades.
I suppose you can define "colour" as including shade as well as hue.

I think that having a different name for a colour is sufficient difference.

What do you say about the "physical colour" of those squares? Is there one colour, or two (brown and yellow?) to match the "perceptual colours"?

Definitely only one physical colour, but two perceptual colours, based on post-processing of cone cell signals in some part or other of the visual cortex.

OK, so 1:2 physical : perceptual is easy. What about the red, green, yellow square. Isn't that 2:1, two physical colours and one perceptual colour?

GrahamH wrote:

DavidMcC wrote:

GrahamH wrote:

DavidMcC wrote:
Acually, it's more a matter of shade than hue. The "brown" and "yelllow" squares do not look like very different hues, just very diffeent shades.
I suppose you can define "colour" as including shade as well as hue.

I think that having a different name for a colour is sufficient difference.

What do you say about the "physical colour" of those squares? Is there one colour, or two (brown and yellow?) to match the "perceptual colours"?

Definitely only one physical colour, but two perceptual colours, based on post-processing of cone cell signals in some part or other of the visual cortex.

OK, so 1:2 physical : perceptual is easy. What about the red, green, yellow square. Isn't that 2:1, two physical colours and one perceptual colour?

Absolutely!
Two or more physical colouyrs can be merged into ne if they are close enough and small enough, yet the final perceived colour is subject to adjustment in the VC, probably to get the best edge visibility.

DavidMcC wrote:

romansh wrote:Last time I did these standardized tests .. I did rather well ... and your point is?

It can't have involved understanding colour vision, then!

Where have I incorrectly represented colour from a technical point of view?

DavidMcC wrote:
Definitely only one physical colour, but two perceptual colours, based on post-processing of cone cell signals in some part or other of the visual cortex.

Which one is the correct perceptual colour?

romansh wrote:

DavidMcC wrote:
Definitely only one physical colour, but two perceptual colours, based on post-processing of cone cell signals in some part or other of the visual cortex.

Which one is the correct perceptual colour?

AFAIAC, there is no "correct" perceptual colour. There is, however, the perceptual colour under standard conditions, such as when it is surrounded only by a wide, white border, and nothing else. This would make the brownish appearance more standard than the yellowish one. However, this is only a matter of convention.

EDIT: If you used a wide, black border instead, the hue would look more-or-less the same, but the shade would seem much brighter.

romansh wrote:

DavidMcC wrote:

romansh wrote:Last time I did these standardized tests .. I did rather well ... and your point is?

It can't have involved understanding colour vision, then!

Where have I incorrectly represented colour from a technical point of view?

Where you claimed that it didn't exist.