re: [cgmo-webcgm] Relative Intensity

[Don Larson <dlarson@cgmlarson.com>]

Forrest,

  > All,

  > This is what we do to control the intensity of colors:

  > 	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);

  > Where intensity has a value from 0 to 1 and the colors range from 0 to
  >  0xffff.

  > What about adopting this as the color intensity method?
This algorithm appears to be converting the RGB value to CMY colorspace
then applying the intesity to all of the CMY values and then back to RGB 
space. 

This has the inverse affect on the color with respect to intensity.

For example with the HLS method when a 50% is applied to the 
color red (255,0,0) it yields (170,0,0) which is a dark red.

With the CMY method when 50% is applied to the (255,0,)
I get a RGB(255,128,128) which is a light red. 

After some more testing, I discovered a dilemma with the HLS 
method. When 50% is applied to the color black RGB(0,0,0) it 
yields RGB(0,0,0) since it has a luminance value of 0. I'm not 
sure that what we want.

In some respects I like Forrest's method. It's a simpler algorithm 
and less likely to be misinterpreted although it has the inverse effect,
ie. lower relative intensity gives a lighter color.


Don. 

  > Regards
  > Forrest