Digital Prints

120
Mastering Digital Printing
A color space is an abstract, three-dimensional range of colors. Photographer Joseph
Holmes describes it as something like a football standing on its end with white at the top
and black at the bottom. A line drawn top to bottom through the center includes all the
grays. The various hues of the visible spectrum wrap around the ball as the colors go from
gray on the inside to their most colorful (saturated) on the outside.
Color consultant C. David Tobie uses the analogy of a tent. The three corners of the tent
are attached to the ground with three tent pegs: Red, Green, and Blue. How far you move
the pegs out determines the size of the tent or color space. The tent is held up in the center
by a pole, which is its gray axis. Raising or lowering the tent on the pole changes the
gray balance and the white point, which is where the pole supports the top of the tent.
Colors further away from the pole are more saturated, those closer, less.
You’ll notice that the two color space descriptions just given closely match the three color
attributes of hue, saturation, and brightness.
Here are the three most important
color spaces for photographer-artists:
LAB
The original CIE color space
(XYZ) was adopted in 1931, and
it identifies color coordinates in
a three-dimensional curved
space. It was adapted to become
the familiar shark-fin-shaped
CIE xyY Chromaticity Diagram
(see Figure 4.5) for easier displaying
in 2D space. (Chromaticity refers to the color properties of hue and saturation only.)
Between them, “x” and “y” define any color’s hue and fullness of color or saturation. The
“Y” is a little hard to grasp since it runs perpendicular to the plane of view, and it indicates
the lightness or luminance of the color. In this sense, the xy diagram is the color tent
viewed from above.
Because of difficulties with non-uniform color spacing in the XYZ model, improvements
were made, and in 1976, the CIE added the LUV and then the now-famous CIE LAB (or
just “LAB,” also written “Lab”) color space. The type of LAB used in color conversions is
ICC LAB, which defines three variables in three-dimensional space: L* (pronounced “Lstar”),
a*, and b* (see Figure 4.6). L* refers to lightness, ranging from 0 (dark) to 100
(light). a* refers to the “magenta/cyan” axis ranging from -128 to 127; positive numbers
are “magenta-ish,” and negative ones are “cyan-ish.” b* refers to the “yellow/blue” axis also
ranging from -128 to 127; positive numbers are “yellow-ish,” negative ones are “blue-ish.”
(The reason the color words are in quotes is because the terms are loose. One person’s blue
may be another’s cyan. It’s the numbers, not the words, that count.) Any particular color
that you can see can be pinpointed by its three LAB coordinates. For example, a spot of
blue sky could be identified as L* = 64, a* = -15, b* = -42. (If you want to get even more
Somewhere between a football and a
tent, this wire-frame representation of
the sRGB color space shows LAB
coordinates and L-dimension toning.
To get the full effect, ColorThink
(www.chromix.com) allows you to
spin the graph to see the 3D volume
in motion.
Graphing by CHROMiX ColorThink