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