RE: Eats, Shoots & Leaves page 5

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Evan Kirshenbaum:
[nq:2]The colors you see reflect the relative response of the ... that it will be perceived (by most) as "the same".[/nq]
[nq:1]There are, of course, other models available which ought, in theory, to get closer to reality.[/nq]
I'm not sure what "closer to reality" means here. I'm pretty sure that all of these models are a matrix multiply away from one another. Also, as you note,
[nq:1]The problem is that sooner or later you're going to have to reproduce these colours either on a TV screen or computer model using the RGB model, or in print using the CMYK model.[/nq]
so using anything other than RGB (asuming projection) is going be an approximation that can only lose fidelity.
[nq:1]HSB stands for Hue, Saturation and Brilliance,[/nq]
"Brightness", in my experience. Foley and Van Dam(1) call it "HSV" for Hue, Saturation, and Value. Ah, I see that this one isn't simply a matrix transform away from RGB, although it's still deterministic and computable in constant time. And invertable.
They also talk about "HLS", which is Hue, Lightness, and Saturation; being essentially "a deformation of HSV, in which white is 'pulled' upwards to form the upper hexcone from the V=1 plane." (p. 617)
[nq:1]where "hue" is the colour on a continuous scale from red to violet, and saturation how pure the colour is ... the brilliance. Lab stands for Luminence, a-channel and b-channel, but don't ask me what the heck that's supposed to mean.[/nq]
I suspect that that's what's more commonly known as YIQ and which forms the basis of the US's poor NTSC(2) color television standard. The basic notion is that one component, Y, can be used all by itself as a black-and-white image, while the other two are used to encode the rest of the color.(3) As you might expect, this doesn't do a tremendously good job.
The one thing that it has going for it is that it makes a reasonably good test to see whether you want to put black text or white text on a background of a given color. If you compute the YIQ equivalent of the color and only look at the Y value, it's pretty easy to find a threshold above which black text looks better and below which white text looks better.
(1) J.D. Foley, A. Van Dam, Fundamentals of Interactive Computer Graphics , 1982.
(2) Never Twice the Same Color
(3) If anybody cares:
Y 0.30 0.50 0.11 R
I = 0.60 -0.28 -0.32 * G
Q 0.21 -0.52 0.31 B

Evan Kirshenbaum + HP Laboratories >When you're ready to break a rule,
1501 Page Mill Road, 1U, MS 1141 >you know that you're ready; youPalo Alto, CA 94304 >don't need anyone else to tell

http://www.kirshenbaum.net /
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Michael West:
[nq:1]I suspect that that's what's more commonly known as YIQ and which forms the basis of the US's poor NTSC(2) ... it's pretty easy to find a threshold above which black text looks better and below which white text looks better.[/nq]
Wouldn't testing it for readability make even more sense? So many variables (stroke weight, character spacing, line spacing) are ignored in this formula. I wonder if it is to blame for so many unreadable
web page designs.

Michael West
Melbourne, Australia
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Maria Conlon:
[nq:1]Maria Conlon schrieb:[/nq]
[nq:2]rewboss wrote in part: But I've always heard that the three primary colors are red, *yellow,* and blue. What happened?[/nq]
[nq:1]That's a simplification for the benefit of schoolchildren.[/nq]
Yes, I was a schoolchild when I learned about red, yellow, and blue being the primary colors.
[nq:1]..You were taught about primary colours for pigments, which are actually cyan, magenta and yellow. But cyan looks like sky-blue, and magenta is a sort of purplish red, so your teachers called them "blue" and "red" to avoid confusing you too much.[/nq]
You think? I'm thinking that it was just what was generally accepted at the time. Is that a possibility? (I started first grade in 1949.)

What are schoolchildren taught nowadays? (I guess I should check with my grandson when he gets settled into first grade this fall.)

By the way, thanks to all who answered my question. I never realized that the "primary colors" thing was so complicated!

Maria Conlon
Still humming "Lavender Blue..."
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Evan Kirshenbaum:
[nq:2]The one thing that it has going for it is ... text looks better and below which white text looks better.[/nq]
[nq:1]Wouldn't testing it for readability make even more sense?[/nq]
In between reading the background color from the config file and writing the text to the screen, there's rarely time to run much in the way of human subjects testing.
[nq:1]So many variables (stroke weight, character spacing, line spacing) are ignored in this formula. I wonder if it is to blame for so many unreadable web page designs.[/nq]
I highly doubt it. The only thing it could be blamed for, if anybody used it, was the wrong choice of black or white text against a particular colored background. I used it on fixed-pitch single-font(1) terminals, where people color-coded the background to signal various things and needed to be able to write text that would be readable against whatever color was chosen (on other grounds).

(1) Okay, you had "bold", too.

Evan Kirshenbaum + HP Laboratories >He who will not reason, is a bigot;
1501 Page Mill Road, 1U, MS 1141 >he who cannot is a fool; and he whoPalo Alto, CA 94304 >dares not is a slave.

(650)857-7572
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Steve Hayes:
[nq:1]rewboss wrote in part: [/nq]
[nq:2]Anyway, as I was saying before I so rudely interrupted ... and blue. Everything else is a mixture of these three.[/nq]
[nq:1]But I've always heard that the three primary colors are red, *yellow,* and blue. What happened?[/nq]
It depends on whether you are talking about light or pigments.

Steve Hayes from Tshwane, South Africa
http://www.geocities.com/Athens/7734/stevesig.htm
E-mail - see web page, or parse: shayes at dunelm full stop org full stop uk
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Laura F Spira:
[nq:1]rewboss wrote in part: [/nq]
[nq:2]Anyway, as I was saying before I so rudely interrupted ... and blue. Everything else is a mixture of these three.[/nq]
[nq:1]But I've always heard that the three primary colors are red, *yellow,* and blue. What happened?[/nq]
I'm sure we discussed this about a year ago. I remember being deeply shocked by this apparent change and asking quite a lot of people what they thought were the primary colours. The majority included yellow rather than green which I found reassuring but we are all wrong, it would seem.

Laura
(emulate St. George for email)
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Stewart Gordon:
[nq:1]That's a simplification for the benefit of schoolchildren. You were taught about primary colours for pigments, which are actually cyan, ... is a sort of purplish red, so your teachers called them "blue" and "red" to avoid confusing you too much.[/nq]
At the expense of calling red "orange", blue "violet" and black "brown". Yellow and green are about the only ones they get right..

Stewart.

My e-mail is valid but not my primary mailbox, aside from its being the unfortunate victim of intensive mail-bombing at the moment. Please keep replies on the 'group where everyone may benefit.
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Evan Kirshenbaum:
[nq:2]rewboss wrote in part: But I've always heard that the three primary colors are red, *yellow,* and blue. What happened?[/nq]
[nq:1]That's a simplification for the benefit of schoolchildren. You were taught about primary colours for pigments, which are actually cyan, ... is a sort of purplish red, so your teachers called them "blue" and "red" to avoid confusing you too much.[/nq]
There's an interesting history of color at
http://www.coloryourcarpet.com/History/ColorHistory.html

It implies that CMY is very recent (1990), although I know it was treated in graphics texts by the early '80s, so I don't know how much credence to lend it. Treating red, yellow, and blue as primary appears to go back to 1613. Painters evidently simply moved their "red" and "blue" closer to to magenta and cyan with the introduction of things like "Prussian blue".

Evan Kirshenbaum + HP Laboratories >So when can we quit passing laws and
1501 Page Mill Road, 1U, MS 1141 >raising taxes? When can we say ofPalo Alto, CA 94304 >our political system, "Stick a fork

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Sara Lorimer:
[nq:1]I don't believe in purple...if it's qualitatively different from blue, an awful lot of things called green need to have names of their own as well..[/nq]
My 19-month-old son thinks all colors are purple ("puh-puh").

SML
http://pirate-women.com
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