>That depends. In rgb-calculations cyan is the opposite of red, if for
instance
>you were using another hightech multimedia-tool like for instance
fingerpaint
>you'd have green as the opposite of red.


This is not entirely true. There is a common misunderstanding, that additive
colors (light) behave different from subtractive (pigments). It is correct
that green is the opposite of red, but the misunderstanding lies in what is
"red" and what is "green".

Here is a show-off from a class I attended once. (This is for information,
and not to make a fool of anyone. It is not easy to come up with all this
one ones own; I know. :) )

Usually, you say that red, blue and yellow are mixed together to make black.
In pigment-theory, yellow is a primary color, which is true, because yellow
pigment is the pigment that reflects everything which is not blue! Red is a
primary color in both systems, however the color is not the same! Red is the
pigment that reflects all colors but green. The red pigment reflects
red+blue light when illuminated with white light, and thus "red" is not
actually red, but red+blue=magenta! "Blue" pigment is really cyan. We have:

"red" (magenta) pigment = <1, 1, 1> - green
yellow pigment = <1, 1, 1> - blue
"blue" (cyan) pigment = <1, 1, 1> - red

The opposite color is the color on the "other side" of the color wheel. Now,
we can see that red is the opposite of green in common language, but it is
actually magenta that is the opposite color of green and vice versa.

If you open the standard color-picking tool in Windows or any graphical
package, you can see the color-wheel, and verify this.

Observe that opposite colors also exists in light-systems, as opposite = <1,
1, 1> - original.

Simen.

Post a reply to this message

Peter Popov wrote:
> 
> On Tue, 28 Sep 1999 14:05:05 +0200, Remco de Korte
> <rem### [at] xs4allnl> wrote:
> 
> >That depends. In rgb-calculations cyan is the opposite of red, if for instance
> >you were using another hightech multimedia-tool like for instance fingerpaint
> >you'd have green as the opposite of red.
> 
> I'm not sure but I think you are talking about the CMY(K) color model
> which is a subtractive one as opposed to RGB which is additive.
> 
> Peter Popov
> ICQ: 15002700

No, not really, although it's close. CMYK is for print as opposed to RGB for
tubes. Obviously print works more or less the same as paint but there are subtle
differences. I guess that has something to do with the tricks of the trade. One
of the most interesting things: paint has mass. But this is totally off topic
here. 8) 

Regards,

Remco

Post a reply to this message

Simen Kvaal wrote:
> 
> >That depends. In rgb-calculations cyan is the opposite of red, if for
> instance
> >you were using another hightech multimedia-tool like for instance
> fingerpaint
> >you'd have green as the opposite of red.
> 
> This is not entirely true. There is a common misunderstanding, that additive
> colors (light) behave different from subtractive (pigments). It is correct
> that green is the opposite of red, but the misunderstanding lies in what is
> "red" and what is "green".
> 
> Here is a show-off from a class I attended once. (This is for information,
> and not to make a fool of anyone. It is not easy to come up with all this
> one ones own; I know. :) )
> 
> Usually, you say that red, blue and yellow are mixed together to make black.
> In pigment-theory, yellow is a primary color, which is true, because yellow
> pigment is the pigment that reflects everything which is not blue! Red is a
> primary color in both systems, however the color is not the same! Red is the
> pigment that reflects all colors but green. The red pigment reflects
> red+blue light when illuminated with white light, and thus "red" is not
> actually red, but red+blue=magenta! "Blue" pigment is really cyan. We have:
> 
> "red" (magenta) pigment = <1, 1, 1> - green
> yellow pigment = <1, 1, 1> - blue
> "blue" (cyan) pigment = <1, 1, 1> - red
> 
> The opposite color is the color on the "other side" of the color wheel. Now,
> we can see that red is the opposite of green in common language, but it is
> actually magenta that is the opposite color of green and vice versa.
> 
> If you open the standard color-picking tool in Windows or any graphical
> package, you can see the color-wheel, and verify this.
> 
> Observe that opposite colors also exists in light-systems, as opposite = <1,
> 1, 1> - original.
> 
> Simen.

If you open the standard color-picking tool in Windows you are again relying on
a computerized, scientifically based, interpretation. I'm not debating what
you're saying here. As I already stated: it's not clear what everyone means by
red although there is some common idea about that. If you're looking at the
difference between blue and green it's getting more difficult as a thread in the
binaries.images group illustrates. Apart from the fact that it is sometimes hard
to decide if it's more green or more blue there is also the problem that not
everyone sees it in the same way. A significant part of the male population is
simply colourblind.

It is tempting, if you're working with computers, to pin down colours on their
values, use a scientific approach. I'm not saying there's anything wrong with
that. My point is: colours are a matter of perception. This is not less
scientific as there has been a lot of research on how people react on colours.
The Bauhaus gave a lot of attention to colour-theory, partly based on artistic
principles, but also on psychological research. You could say that that theory
is outdated but I think there's more in those theories than just some
numbercrunching.

Regards,

Remco

Post a reply to this message

I agree, but there is one fact that has to be made clear, and that is that
many colors are "standarized". I believe (but are not sure) that the colors
in "colors.inc" is taken from the international catalog, which states what
blending of frequencies to use for a specific colour. There are standards to
what one should call "aquamarine", "azure" and so forth. "Blue" and "green"
are more diffuse in the meaning. Many would for example say that the sky is
blue, but that might not be the correct technical term to use. I am not very
bewandered with this; i just happen to know the story behind, if you see
what I mean.

Just another point. A curious fact that I guess you are aware of: Many
colors cannot even be displayed on a computer screen, even with 500 billion
zillion shades of red, green and blue, merely because the human eye can
percieve many more colors. For example, if you have a yellow marking pen and
try to recreate the color on the screen, you'll be dissappointed. If you
scan it you might not even see it!

In the future I think we will get new computer screens wich cover more of
the human eyes capability to see colors. Maybe POV-ray should be able to
extend the usual color-system. One could add infra-red channels, for
example. (We cannot see those frequencies, but they might have scientifical
importance. Who knows.)

Simen.

Post a reply to this message

>No, not really, although it's close. CMYK is for print as opposed to RGB
for
>tubes. Obviously print works more or less the same as paint but there are
subtle
>differences. I guess that has something to do with the tricks of the trade.
One
>of the most interesting things: paint has mass. But this is totally off
topic
>here. 8)


Light has mass too! According to Einstein, light has no resting mass, but
relativistic mass. It is easy to verfy. The solar winds, for example, can
make a satelite go off couse. And you cannot have force without mass. But,
as you say, this is off topic.

Simen.

Post a reply to this message

Simen Kvaal wrote:
> 
> I agree, but there is one fact that has to be made clear, and that is that
> many colors are "standarized". 

Uhm, this is way off topic again, but standardization seems to be on of the
major diseases of these times. Or better: not the standardization itself but the
false belief in it. 
This is a computer based platform: that is on of the places were you can
experience the consequences of Standardization all the time. 

I believe (but are not sure) that the colors
> in "colors.inc" is taken from the international catalog, which states what
> blending of frequencies to use for a specific colour. There are standards to
> what one should call "aquamarine", "azure" and so forth. 

Yes there are. 
Kodak tried to set some standards for instance. 
Of course Apple had to define some standards.
There are probably as many colorstandards as there are, just to name a thing,
computerplatforms. 
Luckily you see standards converging, but you can never be sure.
I thought Netscape's 256 color palette was more or less a standard. Who
guarantuees that Microsoft in an attempt to beat its opponents on all fields
won't come up with another standard for Explorer? Well, luckily the 256-colro
days are almost behind us 8)

"Blue" and "green"
> are more diffuse in the meaning. Many would for example say that the sky is
> blue, but that might not be the correct technical term to use. I am not very
> bewandered with this; i just happen to know the story behind, if you see
> what I mean.
> 
> Just another point. A curious fact that I guess you are aware of: Many
> colors cannot even be displayed on a computer screen, even with 500 billion
> zillion shades of red, green and blue, merely because the human eye can
> percieve many more colors. For example, if you have a yellow marking pen and
> try to recreate the color on the screen, you'll be dissappointed. If you
> scan it you might not even see it!

Aha! Now this interesting, also in regard to the original question!
What would be the opposite of ultra-violet? How would you express such a colour
in a vector? Is perhaps the way to define colours as RGB vectors not as perfecet
as we (computer-users) would like to believe?
> 
> In the future I think we will get new computer screens wich cover more of
> the human eyes capability to see colors. Maybe POV-ray should be able to
> extend the usual color-system. One could add infra-red channels, for
> example. (We cannot see those frequencies, but they might have scientifical
> importance. Who knows.)

How about describing light by its frequency?
Now that would be cool. Once POV-Ray could work with that you could even make
EM-raytracings ;)
> 
> Simen.

Have fun!

Remco

Post a reply to this message

Remco de Korte <rem### [at] xs4allnl> schreef in berichtnieuws
37F27701.33A06FB4@xs4all.nl...
>
> How about describing light by its frequency?
> Now that would be cool. Once POV-Ray could work with that you could even
make
> EM-raytracings ;)

The CIE (Commission Internationale de l'Eclairage) standard uses spectrum
measurement to define a colour. IR and UV are not coverd though, they are not
conciderd colour or light. It's the only colour measurement / definition
accepted by ISO. Even in the printing buisiness it's slowly gaining terrain on
pantone etc.

http://www.inforamp.net/~poynton/notes/colour_and_gamma/ColorFAQ.html

http://www.colourware.co.uk/cpfaq.htm

Ingo

Post a reply to this message

Not that it's likely to happen in POV-Ray (I may wish I didn't say that
later, noticing all the changes to POV and it's cousins over the years) it
would be pretty fantastic to see raytracing cover some of the aspects of
light in the realm of wavelength and the corresponding interactions.
Might be neat to see that ultraviolet (well, not see it exactly unless
shifting the spectrum for a fancy render) interact with something and drop
in frequency to emerge as a deep blue indigo or other fluorescent color;
just like certain mineral rocks.
Fact is, as many people must know, the potential for a vast number of
physical realities being simulated always exists given the will and a way.
That's probably the major stumbling block; I know I can't do 1% of the
things I can think of (actual percentage may vary, greatly....) otherwise
I'd be living a dream.

Bob

Remco de Korte <rem### [at] xs4allnl> wrote in message
news:37F27701.33A06FB4@xs4all.nl...
> Simen Kvaal wrote:
> >
> > I agree, but there is one fact that has to be made clear, and that is
that
> > many colors are "standarized".
>
> Uhm, this is way off topic again, but standardization seems to be on of
the
> major diseases of these times. Or better: not the standardization itself
but the
> false belief in it.
> This is a computer based platform: that is on of the places were you can
> experience the consequences of Standardization all the time.
>
> I believe (but are not sure) that the colors
> > in "colors.inc" is taken from the international catalog, which states
what
> > blending of frequencies to use for a specific colour. There are
standards to
> > what one should call "aquamarine", "azure" and so forth.
>
> Yes there are.
> Kodak tried to set some standards for instance.
> Of course Apple had to define some standards.
> There are probably as many colorstandards as there are, just to name a
thing,
> computerplatforms.
> Luckily you see standards converging, but you can never be sure.
> I thought Netscape's 256 color palette was more or less a standard. Who
> guarantuees that Microsoft in an attempt to beat its opponents on all
fields
> won't come up with another standard for Explorer? Well, luckily the
256-colro
> days are almost behind us 8)
>
> "Blue" and "green"
> > are more diffuse in the meaning. Many would for example say that the sky
is
> > blue, but that might not be the correct technical term to use. I am not
very
> > bewandered with this; i just happen to know the story behind, if you see
> > what I mean.
> >
> > Just another point. A curious fact that I guess you are aware of: Many
> > colors cannot even be displayed on a computer screen, even with 500
billion
> > zillion shades of red, green and blue, merely because the human eye can
> > percieve many more colors. For example, if you have a yellow marking pen
and
> > try to recreate the color on the screen, you'll be dissappointed. If you
> > scan it you might not even see it!
>
> Aha! Now this interesting, also in regard to the original question!
> What would be the opposite of ultra-violet? How would you express such a
colour
> in a vector? Is perhaps the way to define colours as RGB vectors not as
perfecet
> as we (computer-users) would like to believe?
> >
> > In the future I think we will get new computer screens wich cover more
of
> > the human eyes capability to see colors. Maybe POV-ray should be able to
> > extend the usual color-system. One could add infra-red channels, for
> > example. (We cannot see those frequencies, but they might have
scientifical
> > importance. Who knows.)
>
> How about describing light by its frequency?
> Now that would be cool. Once POV-Ray could work with that you could even
make
> EM-raytracings ;)
> >
> > Simen.
>
> Have fun!
>
> Remco

Post a reply to this message

Simen Kvaal <sim### [at] studentmatnatuiono> wrote:
: Light has mass too! According to Einstein, light has no resting mass, but
: relativistic mass.

  I wouldn't say that light actually has mass.
  AFAIK light has no mass. Period.
  This is only my opinion of what I have understood about physics:
  For some calculations it may be easier to consider the light having mass,
but it's only a mathematical trick. It doesn't really have any mass. The
reason why light bends near massive objects is because the space is curved
there and the light tends to move along the geodesic lines of the space
(which are actually the shortest way from one point to another). The
massive object doesn't attract the light, it's just bending the space.

: It is easy to verfy. The solar winds, for example, can
: make a satelite go off couse. And you cannot have force without mass.

  You are confused here. Solar wind is not light, it's gaseous matter that
the Sun is emitting (mainly ions). See:
http://www-spof.gsfc.nasa.gov/Education/wsolwind.html

-- 
main(i,_){for(_?--i,main(i+2,"FhhQHFIJD|FQTITFN]zRFHhhTBFHhhTBFysdB"[i]
):5;i&&_>1;printf("%s",_-70?_&1?"[]":" ":(_=0,"\n")),_/=2);} /*- Warp -*/

Post a reply to this message

Nieminen Juha skrev i meldingen <37f31566@news.povray.org>...
>Simen Kvaal <sim### [at] studentmatnatuiono> wrote:
>: Light has mass too! According to Einstein, light has no resting mass, but
>: relativistic mass.
>
>  I wouldn't say that light actually has mass.
>  AFAIK light has no mass. Period.
>  This is only my opinion of what I have understood about physics:
>  For some calculations it may be easier to consider the light having mass,
>but it's only a mathematical trick. It doesn't really have any mass. The


Light has mass. Period!! It's not just a mathematical trick. Light *has*
relativistic mass, and so have you. When travelling faster and faster, you
gain weight. You cannot travel at the speed of light, because you'd have
infinite mass:

m = m0 / sqrt(1 - (v*v/c*c))

If m0 is your resting mass, v is your velocity and c is the speed of light,
then relativistic mass (aka REAL mass) is m. You can see from the equation
that when your speed approaches the speed of light, your mass diverges into
infinity. These are the equations Einstein found, and they have been
*empirically* verified!

The reason why light has mass, is Einsteins formula:

E = mc^2.

Light has energy, right? Then, light must have mass. It cannot have resting
mass, because light doesn't rest. But as the light travels at the speed of,
say, light, it must have relativistic mass. The energy of a photon is:

E = f * k

where f is the frequency and k is a constant (which i cannot remember; it's
three years since i learnt this). Put this into the "emc" and you get:

m = f*k/c^2

This is the mass of light. Period.




>reason why light bends near massive objects is because the space is curved
>there and the light tends to move along the geodesic lines of the space
>(which are actually the shortest way from one point to another). The
>massive object doesn't attract the light, it's just bending the space.
>

Correct, afaik.


>
>  You are confused here. Solar wind is not light, it's gaseous matter that
>the Sun is emitting (mainly ions). See:
>http://www-spof.gsfc.nasa.gov/Education/wsolwind.html
>

Okay. I was wrong there. But light has mass! The solar winds was just a
(very) bad example. You can verify that photons actually may cause pressure!
This is the empirical prof of the mass of light. You cannot have pressure
without mass.

Post a reply to this message