4 October 2009 Same Colour Illusion

[Carl Horn]

http://apod.nasa.gov/apod/ap091004.html

G'day, I think I've missed something. It appears that the illusion is trying to tell me that a black square of the 'chess board' is the same colour as a white square. Despite the shadow of the green cylinder, I still think that the colour of square A is different from the colour of square B. What have I missed? Cheers, Carl

[kjardine]

I know it's hard to believe, but the colours of the two squares are exactly the same. You can verify that by copying the image and pasting it into a paint program. If you hover an eyedropper over the squares, you will see that they are both RGB = (120,120,120).

What this shows is that colours as we perceive them are *not* created in the eyes but deep in the brain based upon all kinds of factors and not simply the photons that hit your retina.

Kevin

[lodrigj]

I don't know why this is called the "same color illusion", when it is really just a brightness illusion.

Here is a real "same color illusion"

http://www.purveslab.net/seeforyourself/

It's by Dr. Dale Purves at Duke Universtiy.

Click on the "Brightness Contrast with Color: Cube"

It's the first column, second row, on the left.

Jerry

[JohnD]

Carl,

Go the 'joined up' version, and place your hands on the screen either side of the joined squares, so that the cylinder and other distracting items are covered. The illusion disappears, and the equality of the colour (aka density of the gray) is shown.
Allow a few seconds for your brain to revise its processing!

John

[Carl Horn]

G'day, Thank you, Kevin, Jerry. I now understand what was intended. What was particularly useful was the link you provided, Jerry, which permitted an 'isolation sheet' to cover the background. I got some paper and did the same with the APOD illustration by holding them to the screen and masking everything except the A and B squares. They do appear identical when that is done. And revert back when the paper is removed. Isn't that interesting! Cheers, Carl

[Carl Horn]

And thanks to John, too, for your advice. Cheers, Carl

[jerbil]

The post also refers to the "Moon close to the horizon" illusion, which makes people think that the Moon appears larger than when it is high in the sky. An easy way to show that the illusion is not fact is to stretch ones arm out so that one's thumbnail is visible. The angular size of one's thumbnail always possesses a constant ratio to that of the Moon.

All the same, refraction effects do indeed alter the appearance of the Moon. As some textbooks show, near the horizon the Moon (and also the Sun) appears as an ellipse, with relative major and minor axes of (1-a^2) and (1-a) respectively, where a is a very small constant related to the refraction properties of the atmosphere.

[neufer]

So someone remind me again why we are so adamant about humans out to explore other planets?

They can't smell, taste, hear or feel anything...only use their highly calibrated eyesight.

[rstevenson]

So someone remind me again why we are so adamant about humans out to explore other planets? ...

All of the reasons you might get in response can be boiled down to just one. It's fun.

Rob

[neufer]

So someone remind me again why we are so adamant about humans out to explore other planets? ...

All of the reasons you might get in response can be boiled down to just one. It's fun.

Well, perhaps fun & inspiring. So are the Olympics...but Chicago should be celebrating
that Rio will be paying for the building of a one time only use stadium, pool, velodrome etc.

Lets cheer on the Chinese and any others for catapulting naked apes out into space.

As for me, give me more fancy new telescopes & robot spacecraft thanks.

[obscurechemist]

For me the illusion remains even in the "connected" pic.

[polliwog]

after reading everything you guys wrote, i believe you. but i still dont get it. the chess board has black squares and whites squares. the only difference is the shadow from the cylinder. color is not a thing as much as it is a reflection of light off its surface, right? but we clearly have black squares and white squares. and even the "connected" version shows a distinct merging of the colors. we're not comparing the colors of the letters of the squares, are we?

[soupphysics]

I suggest you print the picture, cut out the two squares, or fold the paper, so you can put the two squares next to each other.

The square with the letter A is the exact same color and shade as the square with the letter B.

They appear different, because of the different surrounding colors/shades, and because how your brain knows that it's suppose to be darker in the shadow, and therefore adjusts, so you perceive it differently.

You can also test it by taking a paper and cover everything except the to squares in question, or use a graphics program to get the values of the colors in the two squares. They are the same.

[neufer]

after reading everything you guys wrote, i believe you. but i still dont get it. the chess board has black squares and whites squares. the only difference is the shadow from the cylinder. color is not a thing as much as it is a reflection of light off its surface, right? but we clearly have black squares and white squares. and even the "connected" version shows a distinct merging of the colors. we're not comparing the colors of the letters of the squares, are we?

The various shades of gray are colors.

"These gray and dun colors may be also produced by mixing whites and blacks." - Sir I. Newton.
------------------------------------------
Gray, a. [This is probably the name given to the Greeks, on account of their fair complexion compared with the Asiatics and Africans."Keto bore to Phorcus the Graiae with fair cheeks, white from their birth, and hence they were called Graiae." The Greek word is rendered an old woman, and in this passage of Hesiod, is supposed to mean certain deities. The probability is, that it is applied to an old woman, because she is gray. But the fable of Hesiod is easily explained by supposing the author to have had in his mind some imperfect account of the origin of the Greeks.]

"All cats are grey in the dark."

Attributed to Benjamin Franklin, explaining why to take an older woman to bed,
but appears in John Heywood's book of proverbs (1546) as 'When all candles be out, all cats be gray.'

[bystander]

after reading everything you guys wrote, i believe you. but i still dont get it. the chess board has black squares and whites squares. the only difference is the shadow from the cylinder. color is not a thing as much as it is a reflection of light off its surface, right? but we clearly have black squares and white squares. and even the "connected" version shows a distinct merging of the colors. we're not comparing the colors of the letters of the squares, are we?

You could compare the colors of the letters (they are the same), but the point is that black square A and white square B are in fact the same color of grey.

[soupphysics]

Print it and fold the paper so the two squares touch!

That should be the easiest and most convincing way for you.

[polliwog]

thanks guys. i did print it. it matches.

[Storm_norm]

I guess its only truthful and factual to point out that illusions do exist when looking at the sky with the naked eye/through a telescope, etc... and I guess its only logical to NOT misinterpret these illusions so as to better understand our surroundings.

I am thankful, nonetheless, that knowing the truth behind these illusions does not take away my amazement at just how large that full moon looks on the horizon, or how twinkly those stars look peering down on me, or how orange and calm the sun looks at sunset veiled in whispy clouds. forgetting the truth in these cases is sweet bliss on my eyes.

however,

knowing that we can find out the truth behind these illusions is sometimes equally as bliss.

[Hugh]

Kevin and Jerry explain the "color" illusion well. The only confusion is over the term color. Jerry's use of the term "brightness" is more accurate than "color" in this case as it expresses the amount of light or dark to the eye as opposed to the amount ("intensity") of redness or blueness which is what we think of as color. The import of using the term "brightness" is that it can help in further explaining that the illusion, in this case, is a function of the eye chemistry as influenced by the adjacent brightness. Because the B square is surrounded by darker squares (than the A square's surround) it appears that the B square is brighter.
"Color" becomes a useful term when discussing other types of illusions: Say if you surround square "B" with Red, what color would square "B" appear?

[neufer]

The only confusion is over the term color.

There seems to be some confusion over the spelling as well.

<<Most words ending in an unstressed -our in the United Kingdom and Australia (e.g., colour, flavour, honour, neighbour, rumour, labour) end in -or in the United States (e.g., color, flavor, honor, neighbor, rumor, labor). Wherever the vowel is unreduced in pronunciation, this does not occur: contour, velour, paramour, troubadour, are spelled thus the same everywhere, with "contour" being an important technical term in mathematics and meteorology. Most words of this category derive from Latin non-agent nouns having nominative -or; the first such borrowings into English were from early Old French and the ending was -or or -ur. After the Norman Conquest, the termination became -our in Anglo-French in an attempt to represent the Old French pronunciation of words ending in -or, though color has been used occasionally in English since the fifteenth century. The -our ending was not only retained in English borrowings from Anglo-French, but also applied to earlier French borrowings. After the Renaissance, some such borrowings from Latin were taken up with their original -or termination; many words once ending in -our (for example, chancellour and governour) now end in -or everywhere. Many words of the -our/-or group do not have a Latin counterpart; for example, armo(u)r, behavio(u)r, harbo(u)r, neighbo(u)r; also arbo(u)r meaning "shelter", though senses "tree" and "tool" are always arbor, a false cognate of the other word.

Some 16th and early 17th century British scholars indeed insisted that -or be used for words of Latin origin (e.g. color) and -our for French loans; but in many cases the etymology was not completely clear, and therefore some scholars advocated -or only and others -our only.

Webster's 1828 dictionary featured only -or and is generally given much of the credit for the adoption of this form in the United States. By contrast, Dr Johnson's 1755 dictionary used the -our spelling for all words still so spelled in Britain, as well as for emperour, errour, governour, horrour, tenour, terrour, and tremour, where the u has since been dropped. Johnson, unlike Webster, was not an advocate of spelling reform, but selected the version best-derived, as he saw it, from among the variations in his sources: he favoured French over Latin spellings because, as he put it, "the French generally supplied us." Those English speakers who began to move across the Atlantic would have taken these habits with them and H L Mencken makes the point that, "honor appears in the Declaration of Independence, but it seems to have got there rather by accident than by design. In Jefferson’s original draft it is spelled honour." Examples such as color, flavor, behavior, harbor, or neighbor scarcely appear in the Old Bailey's court records from the 17th and 18th century, whereas examples of their -our counterparts are numbered in thousands. One notable exception is honor: honor and honour were equally frequent down to the 17th century, Honor still is, in the U.K., the normal spelling as a person's name.

Derivatives and inflected forms. In derivatives and inflected forms of the -our/or words, in British usage the u is kept before English suffixes that are freely attachable to English words (neighbourhood, humourless, savoury) and suffixes of Greek or Latin origin that have been naturalized (favourite, honourable, behaviourism); before Latin suffixes that are not freely attachable to English words, the u can be dropped (honorific, honorist, vigorous, humorous, laborious, invigorate), can be either dropped or retained (colo(u)ration, colo(u)rize), or can be retained (colourist). In American usage, derivatives and inflected forms are built by simply adding the suffix in all environments (favorite, savory, etc.) since the u is absent to begin with.

Exceptions. American usage in most cases retains the u in the word glamour, which comes from Scots, not Latin or French. "Glamor" is occasionally used in imitation of the spelling reform of other -our words to -or. The adjective "glamorous" omits the first "u". Saviour is a somewhat common variant of savior in the United States. The British spelling is very common for "honour" (and "favour") in the stilted language of wedding invitations in the United States. The name of the Space Shuttle Endeavour has a u in it since this spacecraft was named for Captain James Cook's ship, the HMS Endeavour.

The name of the herb savory is thus spelled everywhere, although the probably related adjective savo(u)ry, like savour, has a u in the U.K.. Honor (the name) and arbor (the tool) have -or in Britain, as mentioned above. As a general noun, rigour (/ˈrɪɡər/) has a u in the U.K.; the medical term rigor (often pronounced /ˈraɪɡɔr/) does not. Words with the ending -irior, -erior or similar are spelled thus everywhere and have never had a "u", for example inferior or exterior.

Commonwealth usage. Commonwealth countries normally follow British usage. In Canada -or endings are not uncommon, particularly in the Prairie Provinces, though they are rarer in Eastern Canada. In Australia, -or terminations enjoyed some use in the 19th century, and now are sporadically found in some regions, usually in local and regional newspapers, though -our is almost universal. The name of the Australian Labor Party, founded in 1891, is a remnant of this trend.

New Zealand English (e.g., Carl Horn) , while sharing some words and syntax with Australian English, follows British usage.>>

[readm]

Small point: you could have also seen this same APOD on July 17, 2007

[neufer]

Small point: you could have also seen this same APOD on July 17, 2007

So the illusion is time invariant.

[Rob_K]

Nice illusion & seen many times before, but tried something new with it. Head sideways, cross eyes, move square A over square B, and run them around a little so there's a bit of overlap. Voila, the illusion is maintained, at least in my eyes!! One dark, one bright - any explanations? (optical please, I know that they're the same).

Cheers -

Rob

[neufer]

Nice illusion & seen many times before, but tried something new with it.

Head sideways, cross eyes, move square A over square B, and run them around a little so there's a bit of overlap.

Warning: This procedure is not recommended if you are pregnant,
planning to become pregnant, or could become pregnant during this procedure.

[DavidLeodis]

Is there a particular reason why the green cylinder is there (assuming it is green and not an illusion! ) as the illusion works without it.