Chapter 1 Measuring Color
Light Sources: What we see is light that has been refle
cted from or transmitted through the objects.
Comparison of the relative spectral distributions for typical tungste
n (dotted line) and fluorescent (solid line) light sources.
Relative spectral power distributions for three of many ty
pes of day-light illumination. It can vary greatly dependin
g on solar altitude, weather, and atmospheric conditions.
In this imaging system, there are six different light s
ources that contribute to the recording, reproduction,
and viewing of colors.
Objects
Spectral reflection of a red Cortland apple. The apple
generally is seen as red because it reflects a greater f
raction of red light that of green light or blue light.
Spectral reflectance of an ageratum. The flower appears b
lue, even though it seems to have more red-light reflecta
nce than blue-light reflectance.
Spectral reflectance of a particular fabric sample. The
fabric appears green, despite its having spectral char
acteristics that seem to indicate otherwise.
Color Stimuli
Spectral power distribution for a Cortland apple, illuminat
ed with a fluorescent light source. In color science, such p
ower distributions are called color stimuli.
Calculation of the spectral power distribution of a color sti
mulus. The distribution is the product of the spectral pow
er distribution of the light source and the spectral reflecta
nce of the object.
Comparison of the spectral power distributions for the tw
o stimuli-an apple illuminated by a tungsten light source (
dotted line) and the same apple illuminated by a fluoresc
ent light source (solid line).
Human Color Vision
Color theory explained - An eye for color tutorial - YouTube.url
Estimated spectral sensitivities,
,
of the three ty
pes of photoreceptors of the human eye.
The sensitivity of the human visual system rapidly
decreases above 650nm, so the flower looks blue despite its
reflectance at longer wavelength.
The fabric looks green despite its high reflectance at shor
ter and longer wavelength.
An example pair of metameric color stimuli. The two stim
uli produce equivalent stimulations of the eye’s photorece
ptors. Metameric stimuli match in color appearance when
viewed under identical conditions, but they have different
spectral power distributions.
Spectral power distributions for an original color stimulus
and a metameric (visually equivalent) color stimulus prod
uced by a CRT.
CIE Colorimetry
Figure 1.18
Calculation of CIE
XYZ tristimulus
values.
Other Color Measurements