Specifications

CHAPTER 3
Application Program Interface
VPTEngine Component 33
circuitry also allows the host CPU to calculate the observed color of any pixel on the
screen.
Ambient Light 3
Ambient light is the light surrounding your display, and it makes a difference to the way
colors appear on the screen. Ambient light may be normal window light, sunlight,
incandescent light, fluorescent light, and so on. To get a true color rendering, you should
first set the white point for the display and then correct for ambient light.
VPTEngine Component Data Types 3
This section describes the data structures unique to the VPTEngine component. They are
Tristim (XYZ) , CIE1976 (u’v’) , CIE1960 (uv) , CIE1931 (xy) , Kelvin , and
VPTGamma .
These data structures define the “color space ” of the display. Over the years, a number
of notations for colors have been developed. Most of these notations are considered to be
color spaces because they define absolute three-dimensional spaces where colors reside.
The standard RGB notation used on the Macintosh (and on many other computers) is not
a real color space because it has no absolute representation. In other words, if R, G, and B
are all set to maximum, you usually get white. However, these settings do not define
exactly the shade of white you get, since there are many definitions of white.
The Commission International de l’Eclairage, also known as the International
Commission on Illumination, and referred to in this developer note as the CIE
Committee, has created some of the most useful color standards. These are the color
space standards referenced in the following sections.
Tristim (XYZ) 3
This data structure is used to represent the Tristimulus color space. This color space was
first defined in 1931 by the CIE committee.
typedef struct Tristim
{
doubleX;
doubleY;
doubleZ;
} Tristim;
X, Y, Z Standard elements of the Tristimulus (XYZ) notation.