|Recently purcased the book "Illumination and Color in Computer Generated
|Imagery" by Roy Hall. Great book. In this book, he gives the color
|coordinates of each square of the Macbeth ColorChecker(r) chart using
|CIE 1931 XYZ coordinates. I ran out & bought one of these charts at
|my local camera store, and started writing a program to calibrate my
|computer's display. The chart came with a leaflet which lists the
|color coordinates of each square on the chart, but it contains different
|numbers! It also claims to be using the CIE 1931 system, but the three
|columns are labelled " x y Y " instead of " X Y Z ". Anybody know what's
|going on here?
The "x y Y" system is a normalized form of the
"X Y Z" color coordinate space.
x = ---------
X + Y + Z
y = ---------
X + Y + Z
Note that x + y <= 1.0 in this system, and that the
locus x = 1/3, y = 1/3 exhibits equal energy contribution
from each part of the visible spectrum. The Y component
in both systems represents the luminosity function, which
is a measure of perceived brightness independent of color.
Because the "x y Y" system is normalized, Y can be scaled
to any arbitrary reference value.
,u, Bruce Becker Toronto, Ontario
`\o\-e UUCP: ...!uunet!mnetor!becker!bdb
_< /_ "I still have my phil-os-o-phy" - Meredith Monk