Re: Percent of what? A proposal

On Wed, 17 May 2006 10:46:37 +0800 ironcorona <iron.corona@xxxxxxxxx> wrote:
| phil-news-nospam@xxxxxxxx wrote:
|
|> |> "Vague"? OK, maybe I meant that %'s meaning is too dependent on the
|> |> context in which it is used,
|> |
|> | They have to be dependent on the context in which they're used. They
|> | are fractions of something. What they are fractions of dependents on
|> | what they are and on where they are in relation to something else.
|>
|> And you have to know that in order to do the calculation correctly.
|
| So you're saying it would be better to have 18 new values ALL of which
| can only be used in certain contexts. Surely you'd have to be aware of
| where it's appropriate to use each of the new values too. Which means
| you have exactly the same problem but now you can choose from one of
| eighteen different solutions.

What 18 values? The gamma curves for monitors? Did you make up "18"?

Two values need to be known. One is the default gamma that values which
already have the gamma correction applied used. For sources based on
PCs of "IBM compatibility" fame, that's about 2.2. The other value that
needs to be known is what the actual monitor in use has. The windowing
system should know that, and making available to the browser. Then the
browser will perform the correct calculations based on knowing these two
values. CSS's role is to not make the mistake of specifying that the
coded color values are assumed to be linear. If it were to make such a
mistake, we'd have browsers doing the calculations wrong, more meseed up
colors, and more hacks of people trying a variet of different non-standard
ways to compensate for such a mistake.

Assuming 2.2 for the gamma value of the coded colors is relatively safe.
Color values from the Macintosh world might not be so safe. What CSS
could do is provide a means to specify, broadly, or specifically, what
gamma value applies to the coded color values in a given .CSS file.
It probably should default to 2.2. But it provies a means for the
developer that uses other gamma values (assuming the developer even
understands what this is ... apparently way too many don't) to say
what they are. You could read the PNG image format specs to see how
they handle this (GIF didn't handle it at all).

Armed with the two values (which might be the same) the browser can then
correctly perform percentage of color type calculations by first converting
all values to linear using the source gamma value, then converting to gamma
corrected values again using the system display gamma value.

BTW, if there are no percentages of colors being applied, and if the source
gamma and display gamma are the same, no conversion calculations are needed.


|> |> Gamma correction: do some research if you don't know what it's about.
|> |> Check out http://www.geocities.com/therealbirdin/Standards/#sRGB where
|> |> I think I did a semi-decent job of explaining why it's important.
|> |
|> | Why are people giving me pointers to gamma correction? I never asked.
|> | The % value isn't to do with gamma it's simply to do with a percentage
|> | of an 8 bit number.
|>
|> Which is a totally assinine way to calculate intensity values.
|
| Why, semantically it's perfectly correct. It's like saying that a 50%
| of a box of width:300px; is 150px. You don't need to be concerned about
| the area. You don't need to be concerned about the position of the
| moon. Everyone understands that 50% of the width value means the width
| value divided by 2.

You need to be concerned with gamma correction if you want to do the color
calculations correctly. Ignore gamma and you could be doing it wrong.


|> You would
|> know that if you understood gamma correction and how calculations that do
|> not take it into consideration affect chromaticity.
|
| You would know if you understood the spec what it's actually a
| percentage of. Every time you mention gamma it's still not about gamma.
| You could just reply to EVERY post with the words "GAMMA GAMMA GAMMA"
| and it still wouldn't be about gamma. It's not about gamma. How don't
| you understand that.

You are so ignorant about how video works it's shameful.


|> This is why I asked my question of you in the first case. I want to see
|> if you genuinely understand color, and how gamma correction affects it.
|> I'll try the question in a different way: If your intention is to get a
|> gray value which is exactly half the intensity of the color #ffffff, what
|> will be the code you would expect to see as a result?
|
| I wouldn't be. I never even think of the colour intensity. If I want a
| gray value I'll go into paint, double-click gray, move the lum pointer
| up and down until I get a colour I like, translate the rgb values into
| hex and there it is.

If you use a WYSIWYG color selector, you can get what you want. But if
you want to take percentages of those colors, you need to apply that in
the linear value domain, NOT in the coded value domain that you see in
expressions like "#ffffff". Do the calculations for me and see what you
get ... your source gamma is 2.2, your display gamma is 2.45, you want a
50% intensity of #ffffff, what do you get? I'll bet you either won't, or
can't, do this calculation yourself, correctly.

--
-----------------------------------------------------------------------------
| Phil Howard KA9WGN | http://linuxhomepage.com/ http://ham.org/ |
| (first name) at ipal.net | http://phil.ipal.org/ http://ka9wgn.ham.org/ |
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.

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