digital Artform wrote:

So lets talk about light, then.

Unfortunately I have to run. But I'm happy to resume later.

Challenge me on some point and I'll see if I can answer it after my shower but before I leave.

And when you do answer this.....

Why do you see white on your CRT monitor?
and why do you see white in a bright white paper?

What is the difference between the two situation?

Chris Macan wrote:
And when you do answer this.....

Why do you see white on your CRT monitor?
and why do you see white in a bright white paper?

What is the difference between the two situation?

Sorry, I came in late.

Is this a rhetorical question or do you really want an answer?

EDIT:  Looks rhetorical.  Riddle me this, then:

Magenta and purple are on the color wheel but not on the spectrum.  Discuss.

Alexander Image wrote:
Yes! Changed! Changed! Changed!
Why???
Because the filter subtracted some colors of the WHITE light!

Change 'subtracted' to 'multiplied by a fraction between 0 and 100%' and you've got it

Monad Studios wrote:
Sorry, I came in late.

Is this a rhetorical question or do you really want an answer?

EDIT:  Looks rhetorical.  Riddle me this, then:

Magenta and purple are on the color wheel but not on the spectrum.  Discuss.

because the prism doesn't bend short wavelengths in the same vicinity as long ones - and it doesn't 'wrap around' - hence no magenta

except on my shiny CD, wher it does seem to repeat spectrum patterns and therefore 'wrap around'

digital Artform wrote:
Instead of multiplicative color?

Sandwiching two colored filters together is simulated by the 'multiply' blend mode in Photoshop. If subtraction were occurring then it would matter which layer was on top since A - B does not equal B - A.

"Mixing colored dyes is commonly called subtractive color mixing, but properly it should be called multiplicative color mixing instead, for the following reason: Suppose you know a certain amount of ink attenuates a certain wavelength by a factor of X. If you have twice as much ink, the attenuation will be X2, not 2X."

http://www.av8n.com/imaging/dye-spectra.htm

See kiddies... this is what happens when you spend too much time on them new fangled interwebs... now run along and play.

Seriously... I understand what you are getting at with the whole a-b not being equal to b-a.
But, you are aware that you are try to mix apples with orangutans to produce an inorganic compound.... right?

digital Artform wrote:

Change 'subtracted' to 'multiplied by a fraction between 0 and 100%' and you've got it

"Subtracted" refers to real, physical light, and "multiplied" refers here to numbers represented in a computer that's simulating the subtraction of light.

NewBoldPhoto wrote:

See kiddies... this is what happens when you spend too much time on them new fangled interwebs... now run along and play.

Seriously... I understand what you are getting at with the whole a-b not being equal to b-a.
But, you are aware that you are try to mix apples with orangutans to produce an inorganic compound.... right?

No.

The math is the math. How do you think Photoshop can represent CMYK work? Because the math is worked out. And it ain't SUBTRACTIVE

digital Artform wrote:

because the prism doesn't bend short wavelengths in the same vicinity as long ones - and it doesn't 'wrap around' - hence no magenta

except on my shiny CD, wher it does seem to repeat spectrum patterns and therefore 'wrap around'

There are no purple or magenta wavelengths.

Monad Studios wrote:

"Subtracted" refers to real, physical light, and "multiplied" refers here to numbers represented in a computer that's simulating the subtraction of light.

The last thing real physical light does is subtract. Try to shine or produce some negative light and see.

Monad Studios wrote:
There are no purple or magenta wavelengths.

True. It mixes in your brain when long and short wavelengths come togther

Monad Studios wrote:
There are no purple or magenta wavelengths.

Technically there aren't even red wavelengths. Just short visible ones. The 'redness' is defined in the brain.

digital Artform wrote:
The last thing real physical light does is subtract. Try to shine or produce some negative light and see.

Light can also be added to light.  Shine a red light and a green light at the same spot.  You're adding red light to green light.  That's what's meant by additive mixing.

Additive mixing:  Red + Green = Yellow

Subtractive mixing:  Red + Blue = Purple

EDIT:  Sorry, misread.  Light doesn't subtract.  But filters and reflective surfaces do remove some light while passing on other light.  "Subtract" is the conventional word for that removal.

digital Artform wrote:

Technically there aren't even red wavelengths. Just short visible ones. The 'redness' is defined in the brain.

Technically we're taking all kinds of explanatory shortcuts here.

But there is pure red light:  light that is a single wavelength and is perceived as red.

There is no pure purple light.

Chris Macan wrote:

And when you do answer this.....

Why do you see white on your CRT monitor?
and why do you see white in a bright white paper?

What is the difference between the two situation?

There is no important difference.

In the case of a monitor a wide spread of wavelengths, some from a red emitter, some from a green emitter, and some from a blue emitter come together in your brain. The wide variety of apparently equal strength wavelengths stimulates the perception of white.

On paper a wide spread of wavelengthsis reflected into your eyes where it comes together in your brain. The wide variety of apparently equal strength wavelengths stimulates the perception of white.

Monad Studios wrote:

Technically we're taking all kinds of explanatory shortcuts here.

But there is pure red light:  light that is a single wavelength and is perceived as red.

There is no pure purple light.

Yes, so you only see it when two spectra are laid down side by side causing a wraparound, such as what happens on the bottom of an audio CD, where I DO see magenta.

digital Artform wrote:

There is no important difference.

In the case of a monitor a wide spread of wavelengths, some from a red emitter, some from a green emitter, and some from a blue emitter come together in your brain. The wide variety of apparently equal strength wavelengths stimulates the perception of white.

On paper a wide spread of wavelengthsis reflected into your eyes where it comes together in your brain. The wide variety of apparently equal strength wavelengths stimulates the perception of white.

Wrong.  There are several important differences.

But before we can answer your question you have to tell us what kind of light is illuminating the paper:  sunlight?  neon?  the glow from a computer monitor?

digital Artform wrote:

Yes, so you only see it when two spectra are laid down side by side causing a wraparound, such as what happens on the bottom of an audio CD, where I DO see magenta.

That's nonsense on stilts.  Explain this "wraparound" of yours.

Monad Studios wrote:
Subtractive mixing:  start with all colors (e.g. white) light and subtract some to make a new color.  If you "mix" in a yellow filter (i.e. a filter that subtracts blue light) you create the perception of yellow light. 

Then mix in a magenta filter (a filter that subtracts green photons) and we see red light.

Additive mixing: start with no light (e.g. black) and add some to make a new color.  If you add some red light and then add some green light you create the perception of yellow.

"Multiplicative mixing"  No, not really.  Now we're talking real, actual, physical photons vs. numbers in a computer.

That is the way many people understand it. Yes.

It's just false.

Monad Studios wrote:

Technically we're taking all kinds of explanatory shortcuts here.

But there is pure red light:  light that is a single wavelength and is perceived as red.

There is no pure purple light.

?

What happened to roygbIV?

Monad Studios wrote:

That's nonsense on stilts.  Explain this "wraparound" of yours.

A rainbow laying exactly next to a rainbow.

Do you have a CD?

Look at it. Make magenta.

digital Artform wrote:

That is the way many people understand it. Yes.

It's just false.

Which part is wrong?

Monad Studios wrote:

Wrong.  There are several important differences.

But before we can answer your question you have to tell us what kind of light is illuminating the paper:  sunlight?  neon?  the glow from a computer monitor?

You are really out on a tangent if you are trying to muddle the discussion with white balance issues.

Dobias Fine Art Photo wrote:

?

What happened to roygbIV?

That's it: that's the spectrum.  (Isaac Newton put indigo in there because he had a mystical belief that categories come in sevens.)

Important point here is that the spectrum runs from red to violet; there's no magenta or purple there.

digital Artform wrote:
You are really out on a tangent if you are trying to muddle the discussion with white balance issues.

WB has nothing to do with what I said.

A monitor doesn't produce broad-spectrum light.  Its spectrum has big spikes at red, green, and blue, and doesn't have much in between.

Sunlight has a broad smooth spectrum.

Neon light has a single wavelength, i.e. a spectrum with one big spike.

Monad Studios wrote:

Which part is wrong?

I've explained my position in great detail throughout the thread already.

If ND filters didn't multiply 50% - if they subtracted instead, then they would hardly effect bright light and they would potentially send dim light negative.

Monad Studios wrote:

WB has nothing to do with what I said.

A monitor doesn't produce broad-spectrum light.  It's spectrum has big spikes at red, green, and blue, and doesn't have much in between.

Sunlight has a broad smooth spectrum.

Neon light has a single wavelength, i.e. a spectrum with one big spike.

Who cares? What bearing does that have on anything?

digital Artform wrote:


Through Photoshop multiplication (not subtraction) cerulean blue and hansa yellow make green.

And if you want to review SPIKES, review this diagram

digital Artform wrote:

I've explained my position in great detail throughout the thread already.

If ND filters didn't multiply 50% - if they subtracted instead, then they would hardly effect bright light and they would potentially send dim light negative.

I didn't ask you to explain your position.  I asked you to point to what was wrong with what I said.

Anyway the subtraction/multiplication issue really is applies and oranges.

The multiplication you're referring to is the arithmatic you or PS does in calculating the level of light.

The subtraction that people are talking about is the removal (by absorbtion) of physical light.

digital Artform wrote:

No.

The math is the math. How do you think Photoshop can represent CMYK work? Because the math is worked out. And it ain't SUBTRACTIVE

Alright I'm done laughing...whooo
You are aware that math is a theoretical model of the real world.
And I do still agree with you that it seems a silly name in term of photoshops mathematical model. Which to you think came first: Color Theory or Photoshop?

digital Artform wrote:

Who cares? What bearing does that have on anything?

The relationships of colors to each other can vary depending on the spectrum of the light (and of the photographic material or sensor, and of the ink or monitor).

This is independent of white balance.  Even if everything is perfectly white balanced it is still the case.

NewBoldPhoto wrote:

Alright I'm done laughing...whooo
You are aware that math is a theoretical model of the real world.
And I do still agree with you that it seems a silly name in term of photoshops mathematical model. Which to you think came first: Color Theory or Photoshop?

I have to run for now,

But (even though I already explained this)

Take a 50% red filter and subtract out the OTHER 50% with an identical filter and you get black, right?

Maybe in your world.

In MY world you get a 50% of 50% (multiplied) dark red.

digital Artform wrote:
And if spikes existed in pigments:

Blue and Yellow Dont Make Green (Paperback)
by Michael Wilcox
http://www.amazon.com/Blue-Yellow-Dont- … 0967962870

Your theory seems to depend on this "wraparound" thing.  Please do explain.

Monad Studios wrote:

The relationships of colors to each other can vary depending on the spectrum of the light (and of the photographic material or sensor, and of the ink or monitor).

This is independent of white balance.  Even if everything is perfectly white balanced it is still the case.

Awesome. Now use that to introduce the concept of subtraction into the discussion.

NewBoldPhoto wrote:

Alright I'm done laughing...whooo
You are aware that math is a theoretical model of the real world.
And I do still agree with you that it seems a silly name in term of photoshops mathematical model. Which to you think came first: Color Theory or Photoshop?

Ah, thanks, dude.  I was starting to think I was the only one here who didn't believe in the multiplication of light.

Monad Studios wrote:

Your theory seems to depend on this "wraparound" thing.  Please do explain.

Have you ever seen red laid down close to green, say like in pixels in a monitor? Where the result is YELLOW in your brain, even though no yellow wavelength was present?

That's 'wraparound,' since you seem so attached to the word. Or better, that's juxtaposition.

Monad Studios wrote:

NewBoldPhoto wrote:
Alright I'm done laughing...whooo
You are aware that math is a theoretical model of the real world.
And I do still agree with you that it seems a silly name in term of photoshops mathematical model. Which to you think came first: Color Theory or Photoshop?

Ah, thanks, dude.  I was starting to think I was the only one here who didn't believe in the multiplication of light.

Are you not reading this thread very carefully?

digital Artform wrote:

I have to run for now,

But (even though I already explained this)

Take a 50% red filter and subtract out the OTHER 50% with an identical filter and you get black, right?

Maybe in your world.

In MY world you get a 50% of 50% (multiplied) dark red.

NewBoldPhoto wrote:

Alright I'm done laughing...whooo
You are aware that math is a theoretical model of the real world.
And I do still agree with you that it seems a silly name in term of photoshops mathematical model. Which to you think came first: Color Theory or Photoshop?

I think physics came first. And multiplication describes the process better than subtraction does.

digital Artform wrote:
There is no important difference.

In the case of a monitor a wide spread of wavelengths, some from a red emitter, some from a green emitter, and some from a blue emitter come together in your brain. The wide variety of apparently equal strength wavelengths stimulates the perception of white.

On paper a wide spread of wavelengthsis reflected into your eyes where it comes together in your brain. The wide variety of apparently equal strength wavelengths stimulates the perception of white.

Wrong.....

the CRT monitor is mixing RGB light to creat white,
The paper is reflecting white light.

The important difference is the reason that printers work in CMY and CRT Monitors work in RGB.

The CRT starts with a black tube
and through the introduction or red, green and blue light creates all the colors you see on the screen including white.
This is an example is additive color

Printers work in CMY because they are starting with a white base and they need to trick you eye into seeing all the colors it expects. You can do this with CMY because you can systematically subtract the light reflected to create the illusion of a full tone image. The reflective model that printers and photo printing paper uses works much like the subtractive theory of light.