Science a GoGo's Home Page Forums General Discussion Physics Forum Fab Color Illusion

One of the very best I have ever seen.

It just dos'nt seem credible that A and B are the same color!!!
I suggest you just look,...make up your own mind, go get your
friends opinion....before doing anything else.

(PS.I dont believe it)

http://antwrp.gsfc.nasa.gov/apod/ap070717.html

Too much fun. Even when they are connected they still seem to "fade" from one color to the other.

That's really amazing. I cut and pasted them together, and the colours looked the same. Impossible to see the join.

So, I asked Photoshop for a second opinion. It said the luminosity histograms were identical:

A
Mean: 120.01
Std Dev: 0.28
Median: 120

B
Mean: 119.99
Std Dev: 0.34
Median: 120

wow, thats incredible that our mind could play such horrible tricks on us!
ha, its almost unbeleivable

Mike, that is amazing. I used to be a bit of an artist so I do understand how it works but it's still hard to accept.

I also find it rather hard to accept, Terry.
In fact, maybe we should be be thinking about the shades of the color grey?
Because when I cover the bridge in the second picture with my two fingers.....yes it does revert to two colors! Or is that two shades?

Mike: "two colors! Or is that two shades?"

I was once given an ear-bashing for using the word "beiges" to win a Scrabble game. My opponent insisted that there's only one beige and that variations are 'shades' not colours!

shade: "slightly different color: a color that is a variation on a basic color" - Microsoft® Encarta® 2006

I know that as an artist you accept that our perception of colours is influenced by colours that are nearby. People who make a living through interior decorating presumably use this phenomenon in their work. Rede, it does seem it is "shades" we are talking about here, not "colour" (however we might spell it).

Yes, I think so, but "different colour" means different wavelength. The two shades are actually of the the same (group of) wavelengths at the same energy amplitudes.

Do we, in this case, (falsely) perceive different wavelengths, or different amplitudes, or both?

"Rede, it does seem it is "shades" we are talking about here, not "colour" (however we might spell it)."

Yeah, I think so, too.
P.S. I like spelling it colour, too, even though I'm not a Brit.

Tim: "Yeah, I think so, too."
So, you go with the majority in thinking that we are not perceiving an (apparent) shift in wavelength as well amplitude. Tut-tut, I'm out-voted

No, I dont think we are perceiving a shift in wavelength either.
A shift in wavelength means a shift in colour.
But I have now come to the conclusion that Grey is not a colour?
Black, is not classed as a colour.
And I dont think White is either?
Is'nt Grey, Black with a percentage of White in it or v-versa?
(Pedantic arguement. Hehe)

NASA's cheated us. Therefore, to my mind, A and B show slight differences in amplitude.
B must have a tad more Black in it than A, due to the shadow
cast across it by the green pole? Or am I wrong?

Mike: "Black, is not classed as a colour. And I dont think White is either?"

- 'True black' is possible only in the absence of visible light, and therefore the absence of colour.
- White is the combination of all the colors.

Mike: "But I have now come to the conclusion that Grey is not a colour?...Isn't Grey, Black with a percentage of White in it or v-versa?"

- Since black is the absence of visible light, and white is the combination of all the colors, the grey on your monitor screen is not a mixture black and white - it's a combination of colours, as in white, but at a lesser amplitude.

I contend that the perceived spectral composition of the colours in the squares 'A' and 'B' is not necessarily identical. This, however, could be difficult to prove either way owing to subjectivity.
_____

Mike: "B must have a tad more Black in it than A, due to the shadow cast across it by the green pole? Or am I wrong?"

- A and B are of measurably identical luminosity (see 3rd post from top ^)

"Black, is not classed as a colour. And I dont think White is either?"

Technically, aren't they both colors? I mean, they're both crayons! Look what your'e doing to the children by shifting all that they know! Haha, okay.

Good point Tim, we use the term 'colour' more broadly when referring to colouring agents such as crayons; but in terms of physics, black is not a colour. It's the absence of colour. No photons are radiated in the visible spectrum.

What we call a 'black' crayon appears black because there is very little light energy present. However a spectroscopic analysis of that little bit of light would reveal that it has colour content at either the blue end of the spectrum or the red, or both, but at very low amplitude/energy level. If a crayon radiated no light at all it would have zero colour content, and as mentioned it would not, in terms of physics, be a colour - yet it could be still be called a 'colouring agent'.

A white crayon radiates light at many wavelengths. The spectral analysis in this case would reveal the colours of the rainbow.

Right on. So since we have agreed that Black is not a colour in the scientific sense. Cant we agree that White the exact opposite, since it is composed of an infinite amount of different colours. It cannot be described as any single specific colour. Therefore I dont think White can truthfully be called a colour either? In scientific terms of course.

But I do take your point regarding White and Black crayons, and of the term colour, as used in the 'Colour Illusion.

(This has turned out to be a really interesting topic)

Mike: "So since we have agreed that Black is not a colour in the scientific sense. Cant we agree that White the exact opposite, since it is composed of an infinite amount of different colours. It cannot be described as any single specific colour."

My objection to that is:

Colours are almost never pure. Laser light is an exception. That's to say colours usually consist not of a single wavelength, but of a group of wavelengths. Pastel colours are a clear example. I've never, of course, measured the spectrum of pink, but I'd predict that it contains a broad band of wavelengths, just as white does, but with red dominating.

So, it would seem illogical to exclude white from the colour 'set' on the grounds of the breadth of its spectrum.

I was told in art lessons back in the Cretaceous that neither black nor white were colours. So I guess from an artists point of view this supports what many of you are saying.

Mike's comment, "B must have a tad more Black in it than A, due to the shadow cast across it by the green pole?" is basically correct. You put black into a colour to give the appearance of shadow. The shadow on the light square has made it as dark as the light on the dark square. (I'm of Irish ancestry if you have trouble following that.) Of course purist artists wouldn't use black pigment. They'd mix a brown (the three primary pigments mixed) and add a dark blue. This comes out a more interesting black. I often used to paint using just three primary colours and white.

No, I have to resist that. B is no more black than A. It's the same colour - oh, alright then, it's the same "shade" if you like


- but that's true, even to an Englishman

I'm a co-coordinator of the community outreach program where I work. For the past two years we've put on a "science night" for students, teachers, and administrators in our city. We've had well over 250 students, but lots of parents and teacher attend each year.

This year I put together an optical illusion presentation that included this exact example. I also taped a blank sheet of paper over it, with lift up tabs on the squares A and B. It was a huge hit. Also included other illusions, as well as some autostereograms.