1 of 4
1
Primary Colors
Posted: 04 January 2009 11:11 PM   [ Ignore ]
Sr. Member
Avatar
RankRankRankRankRankRankRankRankRankRank
Total Posts:  633
Joined  2007-12-10

We all know that primary colors are red, yellow, blue, and you can mix them to get the secondary colors green, purple, and orange. This is a result of our minds averaging the intensity and wavelength of the primary colors to create a secondary color.

Why cant our mind average the intensity and wavelength of secondary colors to make a primary? Or am I missing something else?

 Signature 

Dan

Profile
 
 
Posted: 05 January 2009 12:55 AM   [ Ignore ]   [ # 1 ]
Moderator
RankRankRankRankRankRankRankRankRankRank
Total Posts:  5508
Joined  2006-10-22

You can, but the colors are usually muddy.  One problem is if you are using pure pigments or if you are using premixed colors.  For example, if you mix a red pigment with a yellow one, you get orange.  If you mix a good, clean magenta pigment with a clean orange one, you will get a decent red.  But if you mix orange paint that’s been premixed from red and yellow with a magenta paint that’s been premixed from red and blue, you get a muddy one, sort of a reddish brown, because of the blue. 

Another problem is is whether you are doing it by subtraction or addition.  The above were subtraction.  Instead, if you shine a spectrally pure red light and a yellow light on a white surface you will get what appears to be a light orange.  If you shine a magenta and an orange you’ll get a light pink. 

I recall that I was sure that olive drab was mostly a green pigment.  I was surprised to see that it was mostly yellow and black with a bit of red thrown in.

Occam

Profile
 
 
Posted: 05 January 2009 08:08 AM   [ Ignore ]   [ # 2 ]
Sr. Member
Avatar
RankRankRankRankRankRankRankRankRankRank
Total Posts:  9301
Joined  2006-08-29

Primary colors are magenta (pink), cyan (light blue), and yellow. Secondary colors are red, blue (dark blue) and green. I don’t understand your question, but one way to get primary colors out of secondary is in light (in comparison to solid colors). Red, blue and green are the primary colors of light. If you mix all of the light colors you get white, no light will give you black. This is again reversed in solid colors where mixing all colors will produce black, no color is white.

I never actually understood how this works if all we see is light.

Profile
 
 
Posted: 05 January 2009 09:30 AM   [ Ignore ]   [ # 3 ]
Sr. Member
Avatar
RankRankRankRankRankRankRankRankRankRank
Total Posts:  1995
Joined  2008-09-18

This is difficult for me to explain, because I myself don’t have a complete understanding of the issues, but here goes:

The concept of primary colors is misleading. Remember, we’re just talking about light, and all it has are wavelengths. This suggests that any color can be specified by a single number: the wavelength. However, it’s more complicated than that, because what we see is usually a combination of many different wavelengths, which our brain then interprets. We have learned that these combinations can be specified with just three numbers. But there are many fundamentally different sets of three numbers that will do the job, and various specialists prefer different sets. Among these are RGB (red, green, blue); HSB (hue, saturation, brightness); the system George pointed out, whose acronym I don’t recall; and a couple of minor ones.

There is no fundamental superiority of any one system over any other; however, different applications work better with different systems. For example, when you’re adding light, as with computer monitors, RGB is most convenient. But when you’re subtracting light, as with inks, George’s system works best.

But again, there’s nothing physically fundamental about any of these sets. I could create a set based on orange, purple, and mauve, and it would work (assuming those three colors are pure colors; i.e., that each can be represented by light of a single wavelength.)

I hope I haven’t made matters even more confusing.

Profile
 
 
Posted: 05 January 2009 09:38 AM   [ Ignore ]   [ # 4 ]
Moderator
Avatar
RankRankRankRankRankRankRankRankRankRank
Total Posts:  4108
Joined  2006-11-28

I think an important facet of the problem not yet mentioned is the system we have for seeing colors (i.e. wavelengths) in the eye (Color Vision). It’s not jjust the brain, which manipulates input in complex and subtle ways, it’s the retina. The sense of three primary colors is mostly based on the fact that we have three types of color receptors (cones) with specific and relatively narrow ranges of wavelength sensitivities. So we see discrete colors not just because our brain “averages” wavelnegths seen, but primarily because our retinas only respond to specific parts of the visible light spectrum.

 Signature 

The SkeptVet Blog
You cannot reason a person out of a position he did not reason himself into in the first place. 
Johnathan Swift

Profile
 
 
Posted: 05 January 2009 09:45 AM   [ Ignore ]   [ # 5 ]
Administrator
Avatar
RankRankRankRankRankRankRankRankRankRank
Total Posts:  15435
Joined  2006-02-14
mckenzievmd - 05 January 2009 09:38 AM

I think an important facet of the problem not yet mentioned is the system we have for seeing colors (i.e. wavelengths) in the eye (Color Vision). It’s not jjust the brain, which manipulates input in complex and subtle ways, it’s the retina. The sense of three primary colors is mostly based on the fact that we have three types of color receptors (cones) with specific and relatively narrow ranges of wavelength sensitivities. So we see discrete colors not just because our brain “averages” wavelnegths seen, but primarily because our retinas only respond to specific parts of the visible light spectrum.

Right. The phenomenon of having “three primary colors” (whereby any color experience can be perfectly replicated by mixing three colored lights in different intensities) is an artifact of our retinal structure—most humans are “trichromats”, which is to say they have three types of cones, each one sensitive to a particular wavelength of light. Red/green colorblind people only have two sorts of cones. Birds have FOUR sorts of cones, and hence are “tetrachromats”. They have a wider qualitative color space than humans do, and it’s not the case that any three differently colored lights could reproduce all the colors they can see. If you were to make a TV screen for a bird, you would need four sorts of phosphors.

 Signature 

Doug

-:- -:—:- -:—:- -:—:- -:—:- -:—:-

El sueño de la razón produce monstruos

Profile
 
 
Posted: 05 January 2009 09:53 AM   [ Ignore ]   [ # 6 ]
Sr. Member
Avatar
RankRankRankRankRankRankRankRankRankRank
Total Posts:  9301
Joined  2006-08-29
dougsmith - 05 January 2009 09:45 AM

If you were to make a TV screen for a bird, you would need four sorts of phosphors.

And if you were to make a strip club for the birds, it would have to be the guys to do the dancing.  cheese  (Sorry, I couldn’t resist.)

Profile
 
 
Posted: 05 January 2009 10:00 AM   [ Ignore ]   [ # 7 ]
Moderator
Avatar
RankRankRankRankRankRankRankRankRankRank
Total Posts:  4108
Joined  2006-11-28

And if you were to make a strip club for the birds, it would have to be the guys to do the dancing.

LOL

 Signature 

The SkeptVet Blog
You cannot reason a person out of a position he did not reason himself into in the first place. 
Johnathan Swift

Profile
 
 
Posted: 05 January 2009 10:18 AM   [ Ignore ]   [ # 8 ]
Sr. Member
RankRankRankRankRankRankRankRankRankRank
Total Posts:  6195
Joined  2006-12-20
mckenzievmd - 05 January 2009 09:38 AM

The sense of three primary colors is mostly based on the fact that we have three types of color receptors (cones) with specific and relatively narrow ranges of wavelength sensitivities. So we see discrete colors not just because our brain “averages” wavelnegths seen, but primarily because our retinas only respond to specific parts of the visible light spectrum.

When you talk about the visible light spectrum does that mean visible to us? (as I tend to suppose)

We can imagine an environment in which we or other creatures would evolve to see colours at a higher or lower frequency than the visible light spectrum.

Stephen

Profile
 
 
Posted: 05 January 2009 10:54 AM   [ Ignore ]   [ # 9 ]
Sr. Member
Avatar
RankRankRankRankRankRankRankRankRankRank
Total Posts:  1995
Joined  2008-09-18

There’s not a lot of range for broadening of the visible light spectrum. At the red end, quantum efficiencies go down fast, so that you need pretty specialized receptors to perceive infrared. Moreover, thermal radiation starts intruding. That is, you start seeing any hot object as bright. This would be really great if you’re hunting warm-blooded animals, but it would blind you to finer color distinctions for hot objects. In other words,  you might not be able to the tell the difference between a hot ripe fruit and a hot unripe fruit.

At the UV end, your problem is atmospheric absorption, which would impose range limits on your vision. It’s fine for insects, who work at very short visual ranges, but for larger animals, UV is less informative.

Profile
 
 
Posted: 05 January 2009 11:08 AM   [ Ignore ]   [ # 10 ]
Sr. Member
RankRankRankRankRankRankRankRankRankRank
Total Posts:  6195
Joined  2006-12-20
Chris Crawford - 05 January 2009 10:54 AM

There’s not a lot of range for broadening of the visible light spectrum. At the red end, quantum efficiencies go down fast, so that you need pretty specialized receptors to perceive infrared. Moreover, thermal radiation starts intruding. That is, you start seeing any hot object as bright. This would be really great if you’re hunting warm-blooded animals, but it would blind you to finer color distinctions for hot objects. In other words,  you might not be able to the tell the difference between a hot ripe fruit and a hot unripe fruit.

At the UV end, your problem is atmospheric absorption, which would impose range limits on your vision. It’s fine for insects, who work at very short visual ranges, but for larger animals, UV is less informative.

Interesting thanks Chris,

Do insects see UV?

Stephen

Profile
 
 
Posted: 05 January 2009 11:19 AM   [ Ignore ]   [ # 11 ]
Moderator
Avatar
RankRankRankRankRankRankRankRankRankRank
Total Posts:  4108
Joined  2006-11-28

Yes, Chris is right on here. Snakes “see” in infrared, which helps to locate rodents underground but wouldn’t be useful out on the savanna in daytime. Many insectes see in UV, and there are great sets of UV photos of flowers which show very different patterns from those we see, some that look like nothing less than “landing lights” guiding the bees in!

 Signature 

The SkeptVet Blog
You cannot reason a person out of a position he did not reason himself into in the first place. 
Johnathan Swift

Profile
 
 
Posted: 05 January 2009 11:58 AM   [ Ignore ]   [ # 12 ]
Moderator
RankRankRankRankRankRankRankRankRankRank
Total Posts:  5508
Joined  2006-10-22

Chris, it’s the Munsell system that defines colors by hue, chroma, and value. 

George, a good way to envision the way the colors work is to use three clear filters (red, yellow, blue or magenta. cyan, yellow).  If you have one white light source and put one filter in front of it, you get that color, if you then slip another different color filter in front of it, you get the colors that fit in our visual spectrum between the other two.  Then if you slip the third color filter in front of them, you get nothing, that is, black. — Subtraction

If, however, you use three light sources and put one filter on each light source and shine the three spots on a white paper, where the three intersect you’ll get white. — Addition

Occam

Profile
 
 
Posted: 05 January 2009 01:17 PM   [ Ignore ]   [ # 13 ]
Sr. Member
Avatar
RankRankRankRankRankRankRankRankRankRank
Total Posts:  9301
Joined  2006-08-29

Occam,

Is it because the objects in the first example absorb all the light until there is nothing left?

Profile
 
 
Posted: 05 January 2009 01:19 PM   [ Ignore ]   [ # 14 ]
Sr. Member
RankRankRankRankRankRankRankRankRankRank
Total Posts:  6195
Joined  2006-12-20
mckenzievmd - 05 January 2009 11:19 AM

Yes, Chris is right on here. Snakes “see” in infrared, which helps to locate rodents underground but wouldn’t be useful out on the savanna in daytime. Many insectes see in UV, and there are great sets of UV photos of flowers which show very different patterns from those we see, some that look like nothing less than “landing lights” guiding the bees in!

Wow v interesting, TY.

Stephen

Profile
 
 
Posted: 05 January 2009 01:51 PM   [ Ignore ]   [ # 15 ]
Sr. Member
Avatar
RankRankRankRankRankRankRankRankRankRank
Total Posts:  9301
Joined  2006-08-29

I guess the dark matter then must be some sort of a matter after all, since the universe appears dark. Because if this matter didn’t exist, and was not therefore absorbing the light from the stars, the universe would be filled with light. No?

Watch out! A graphic designer playing an astrophysicist…  grin

Profile
 
 
   
1 of 4
1
 
‹‹ Madoff, Ponzi schemes, and religion      Joke ››