Re: Fwd: re: [cgmo-webcgm] New draft snapshot

[Lofton Henderson <lofton@rockynet.com>]

At 11:22 PM 7/12/2004 -0400, Benoit Bezaire wrote:
>Hi all,
>
>Thank you for the information Don.  What we now have to decide is what
>is 'relative intensity' relative to?  To say "Then the desired
>Relative Intensity replaces the luminance component in calculated HLS"
>might not be specific enough.
>
>Here's an example, let's take purple color RGB(171,73,201) with an HLS
>equivalent of HLS(285,54,54).
>
>If I set the relative intensity to 50%, what is the new HLS value:
>HLS(285,27,54) or HLS(285,50,54)?  In other words, is it relative to
>the initial value or relative to the black(L=0%)-white(L=100%) range?
>Given the name 'relative intensity', I suspect we mean the former, is
>that correct?

Don wrote in his proposal, "Then the desired Relative Intensity replaces 
the luminance component in calculated HLS".  That does not seem ambiguous 
-- it corresponds to the 2nd interpretation.

So the question is ... is this what we want?  I can see pros and cons both 
ways.  On the one hand, "double the intensity" or "halve the intensity" 
seems like a useful capability (1st interpretation, brings clamping issue 
with it).  On the other hand, a scale from 0% (black) to 100% (white) makes 
more sense to me (and avoids the clamping issue).

Forrest proposed a different system:

>         new_color.red    = 0xffff - intensity*(0xffff - old_color.red);
>         new_color.green = 0xffff - intensity*(0xffff - old_color.green);
>         new_color.blue   = 0xffff - intensity*(0xffff - old_color.blue);

I need clarification -- is this about subtractive color (ink) or additive 
(luminous)?  Because I was at first reading (0xffff,0xffff,0xffff) as 
white, in which case minimum intensity (=0) would lead to white and maximum 
intensity (=1) leads to "old_color" -- counter-intuitive.  On the other 
hand, if 0xffff is black, it makes more sense.  0 intensity is black, and 1 
intensity is "old_color".  I.e. with this system, what you do is traverse 
the difference from old_color to 0xffff (black or white).  (If subtractive) 
you can get dimmer than old_color but never brighter.

-Lofton.


>If the answer is that it is relative to the initial value, are we
>allowed to make the color 'whiter' by setting an intensity higher than
>100%, for example setting 150% on that purple would make the HLS
>values(285,81,54).  If this is allowed, I presume we should clamp the
>L value at 255, correct?
>
>Please let me know what's your take on this.
>
>--
>Best regards,
>  Benoit                            mailto:benoit@itedo.com