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Name: Red
Status: other
Age: 30s
Location: N/A
Country: N/A
Date: 1999-2001


Question:
Is it true that black is an absence of color (technically NOT a color) and white is a combination of all colors? (Your answer will help my debate with my wife....)


Replies:
Our eyes react to different shades of light, and what we determine as colors are different wavelengths of light. When we say an object is a certain color, it is because it is reflecting more of a certain wavelength light. For example red objects reflect "red" light, or light with a longer wavelength (lower frequency) better than other types of light.

So, we determine the color by the primary type of light the object reflects (or emits if it is a light).

We also perceive other properties of colors, and that is lightness or darkness. A light colored object may reflect one color especially well, but also reflect other colors as well. A very light green object, for example, reflects green very well, but also reflects most other colors, just not as well.

Dark objects tend not to reflect light very well at all, even if it reflects one color better than the other.

White objects, tend to reflect all types of light equally well, and tend to reflect most of the light cast on it.

Black objects also, tend to reflect all types of light equally, they just dont reflect much of the light cast on them.

In computer graphics, we use combinations of just three lights to produce the colors on a screen, red, green, and blue. We also use different systems for calculating colors. One of those is hue, saturation, and lightness. This system is more accurate in describing how we perceive colors. The hue is what we call color--red, brown, white, etc. The saturation is how much of the other colors is present, and the lightness is how bright the color is.

The interesting thing about this system is, white and black have the same hue and saturation, the lightness is all that is different.

Anyway, what all this boils down to, is the answer to your question simply depends on how you look at the problem.

On one level, you are right. Black doesn't reflect light, and white reflects all colors. On the other hand, if you are talking to someone like me who deals with generating colors on a computer screen, black and white are exactly the same color, one is just brighter than the other.

I hope this helps your discussion.

Eric Tolman
Computer Scientist


Well, I think color is best defined as a human sensation. That is, we should define color as that property of visual impression which evokes the word ``red'' when looking at the setting sun and ``blue'' when looking at the daytime sky. From that point of view, white and black are both single, real colors, no less than red or blue or chartreuse.

You may be thinking of defining color in terms of the frequency of the electromagnetic radiation involved, i.e. green light is that of wavelength 5000 angstroms, red light is that of 7000 angstroms wavelength, and so forth. Part of the problem with this definition is that the human eye does not simply analyze the frequencies of incoming light when it perceives color. There are far too few visual pigments for that. Hence the color we perceive does not always correspond to the color of the light received.

For example, an object will be perceived as yellow if it reflects primarily yellow light, BUT ALSO if it reflects not one photon of yellow light but reflects red and green light equally. Furthermore, most people would want to call this object yellow, suggesting the key defining question for color is: how does the eye perceive it?

We run into problems with your definitions of black and white if we try to define color as frequency, also. A certain object may reflect quite strongly in the infrared or ultraviolet, outside the range of human vision, but not at all in the visible. Such an object hardly meets the criterion of reflecting no light of any color, yet it would *look* black, and be called black by any ordinary person looking at it. By the same token, an object could reflect radiation equally across the visible spectrum, and yet have a very complicated dependence on color of its reflectance outside this narrow region. Such an object would *look* and be called white, but does not meet your criterion of reflecting radiation equally at all frequencies (colors).

We cannot even standardize the ``visible'' region. Not all living creatures see in the same color range we do. Spiders see into the infrared and bees into the ultraviolet, and so there are objects that look black to us which are NOT black to spiders, and objects that look white to us that are NOT white to bees. Individual human beings presumably also have some variation in how far up and down in color they can see, just as there is variation in how high and low you can hear.

So I think it is futile to try to match the usual, everyday sense of the word color to anything other than the human sensation in the eye. And by this token black and white share equal status with red and blue.

Let me also mention that a black object has a few definitions, some of which may surprise you. A black hole, for example, is an object that emits no radiation whatsoever. This is close to your meaning, I think. But on the other hand, a black body is one which emits and absorbs radiation of all frequencies equally well. The Sun, for example, is a black body. A rather white and glowing black body, it turns out.

Grayce


Red (interesting name considering your question!),

We call an object 'black' if visible light hitting its surface is not reflected...that is, the light is absorbed by the object and our eyes do not see a color reflected from the surface. We see a plant as green because the plant absorbs wavelengths of visible light including all but green, which is reflected back and is what we see. The same goes for all other colors.

Since we have defined 'color' as the wavelength(s) of visible light reflected from an object, with the remainder being absorbed, a black object has no 'color' by our definition. An object we call 'white' reflects all wavelengths of visible light and therefore could be considered all-colored.

Good luck in your upcoming debate. :)

Thanks for using NEWTON!

Richard R. Rupnik
Internal Quality Auditor
Lucent Technologies


White light contains light of all frequencies. In that sense, white is a combination of all colors. Black objects absorb light of all frequencies. This means that very little light is reflected from them. Black is the absence of light.

As far as the absence of color is concerned... you know that if you combine pigments or dyes of different colors, you don't end up with white. Dyes and pigments work by absorbing light in certain frequency ranges, and transmitting or reflecting light of other frequencies. If two different dyes are combined, the mixture absorbs light characteristic of BOTH dyes, and transmits light of the remaining frequencies. If you mix togtether dyes that are truly complementary, the mixture will absorb light of all frequencies, and thus be black. (In practice the best you can do is get a muddy brown, because the different dyes are only approximately complementary.) So it depends on what you mean by "absence of color."

We perceive colors because we have three types of "cone" cells in our retinas, each of which is most sensitive to certain frequency ranges. These ranges correspond pretty much to red, green, and blue. Our brain interprets the different intensities of the signals from each type of cone cell to decide what color it sees.

Richard E. Barrans Jr.


Light travels in waves and is made up of all of the colors of the spectrum. You can see this when light is bent through the use of a prism. When light hits an object 3 things can happen: it can be absorbed, it can be reflected or it can be transmitted (or shine right through). When white light hits an object, usually some of the light's energy is absorbed by the object. Any part of the spectrum (energy) that is not used by the object is reflected back. The portion of the spectrum that is reflected back is the color that you actually see. For example, the reason that green plants are green is that chlorophyll absorbs light in the blue and red and reflects light in the green and yellow. So black is actually when all the light energy is absorbed and no light is being reflected back. So it isn't really the absence of color, its the absence of any reflected light. White is actually when all of the light is reflected and none of it is absorbed. So it is still made up of all of the colors of the spectrum.

Van Hoeck



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