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A warning about what we perceive

November 29, 2014

Nell Greenfieldboyce, an NPR science correspondent, has an interesting article in one of the National Public Radio blogs. We should see it for its cautionary value to us when we look at the shroud.

These X’s Are The Same Shade, So What Does That Say About Color?,” she proclaims in the title. They are:

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Nell goes on to write:

Mark Fairchild, who studies color and vision science at the Rochester Institute of Technology, says that even physicists get it wrong when they confidently assert that color is just a wavelength of light.

"My usual quick answer to that is I can take any wavelength and make it appear almost any color," says Fairchild.

That’s because color is not something out there in the world, separate from us.

"The agreed-upon technical definition of color," says Fairchild, "is that it’s a visual perception."

So don’t try to tell Fairchild an apple is red. He’ll say, no it’s not, technically — red is just your perception.

"I could change the color of illumination on that apple and make it look green or blue or something completely different," he says. "The redness isn’t a property of the apple. It’s a property of the apple in combination with a particular lighting that’s on it and a particular observer looking at it."

All three of those elements are critical to the idea of "red" or any other color, he says. "You have to have somebody looking at that in order to combine all that information and produce a perception."

Fairchild likes to tell this story:

One night, when his daughter was young, he and his wife decided to have dinner by candlelight. They fed their daughter first, and his wife served macaroni and cheese.

The table was set, the candles were lit. But his daughter took one look and recoiled from her food’s color.

"She started almost crying and getting very upset and yelling at us because we gave her the white macaroni and cheese and not the yellow macaroni and cheese," says Fairchild. "Her favorite is the yellow macaroni and cheese."

Because he studies color perception, Fairchild immediately realized what was going on.

"I said ‘Hold on, stay right there. I can magically turn it into yellow macaroni and cheese,’ " he recalls, "and I walked across the room and I flipped on the lights."

The mac and cheese in her bowl, it turned out was, indeed, yellow. But when it was only illuminated by the candlelight, which is very yellow, the light reflecting off her food had looked almost identical to the light reflecting off the white bowl.

"She just responded to what her eyes created there, the perception her eyes created," Fairchild says. "She thought it was white because it matched the bowl."

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  1. anoxie
    November 29, 2014 at 6:03 am

    “I could change the color of illumination on that apple and make it look green or blue or something completely different,” he says. “The redness isn’t a property of the apple. It’s a property of the apple in combination with a particular lighting that’s on it and a particular observer looking at it.”

    Or if you don’t illuminate that apple, it still glows in the infrared…

  2. November 29, 2014 at 9:02 am

    I’d have swore those X’s were different shades. That’s amazing.

    • clublu22014
      November 29, 2014 at 11:31 am

      Me too… we must be in the same light, Dave.

  3. daveb of wellington nz
    November 29, 2014 at 2:09 pm

    There seem to be at least three elements involved: The mix of light frequencies of illumination; the absorption spectrum of the illuminated object; the perception experience of the observer; possibly a fourth as here, absorption spectrum of object’s surrounds.

    Isaac Newton’s prism experiment was conducted in a dark room with only a narrow beam of incident sunlight focused on his prism and then projected onto a screen. What would he have seen if he had decided he needed a candle to see what he was doing? Would he have not seen the yellow band? Check Google Search on “Images prism light experiment” – there are several examples.

    Nevertheless there are still those who deny the validity of the experiment because of the subjective perceptions and brain chemistry of the observer. And one does not need to be colour blind to deny it.

    • anoxie
      November 29, 2014 at 2:15 pm

      Isaac Newton knew he didn’t need a candle to see what he was doing. He knew what he was doing.

  4. anoxie
    November 30, 2014 at 5:38 am

    Back to the Shroud, from the beginning, filters have been used to enhance details.

    It has always been the basis for image analysis, since the beginning of space exploration, and keep in mind Don Lynn was an image analyst at JPL.

    That’s why physicists and scientists speak of “natural” color, meaning under sunlight.

    See Mars’ images from Olivier de Coursac or more recently, an image from Europa:
    http://www.pasadenanow.com/main/mapping-the-chemistry-needed-for-life-at-europa

  5. November 30, 2014 at 9:08 am

    On the bottom of the Xs, where they cross from yellow to gray, the color of the X appears to change. How could it be measured by an instrument that would prove the assertion?

  6. November 30, 2014 at 2:10 pm

    Print the image out, then cut up the sections and compare them.

    • November 30, 2014 at 2:34 pm

      There’s a quicker way: upload to MS Paint, then frame with white surrounds:

  7. anoxie
    December 4, 2014 at 4:50 am

    “On the bottom of the Xs, where they cross from yellow to gray, the color of the X appears to change. How could it be measured by an instrument that would prove the assertion?”

    Andy, the physical attributes of color doesn’t change.

    The warning points precisely to this distinction between our perception of color (physiologically based- center-surround organization of the receptive fields in the retina) and the physical attributes of color (wavelength-brightness…).

    Then, what happens when you try to compare distant color? You’re doomed. It turns out our eyes are sensitive to local contrast variations but rather ineffective to compare distant points.

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