RE intensity

[Forrest Carpenter <forrest@sdicgm.com>]

All,

My understanding was that we wanted to make some APS fade in color
(go toward white) so other objects would stand out more in the image.
So an intensity of 1 would not change the color and an intensity of 0 would
make it white. Internally  in our applications we convert all colors to a range
from 0 to 0xffff where (0xffff,0xffff,0xffff) is white. If we are going the 
other way
how do you make red more intense, make it black?

Forrest



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.