DigitalVideoAndHDTVAlgorithmsAndInterfaces.pdf

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1. Wideband filter set
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2. Narrowband filter set
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3. CIE-based filter set
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Figure 21.3 Spectral constraints are associated with scanners and cameras. 1. Wideband filter
set of the top row shows the spectral sensitivity of filters having uniform response across the
shortwave, mediumwave, and longwave regions of the spectrum. Two monochromatic sources
seen by the eye to have different colors – in this case, a saturated orange and a saturated red –
cannot be distinguished by the filter set. 2. Narrowband filter set in the middle row solves that
problem, but creates another: Many monochromatic sources “fall between” the filters, and are
sensed as black. To see color as the eye does, the filter responses must closely relate to the color
response of the eye. 3. CIE-based filter set in the bottom row shows the color-matching functions
(CMFs) of the CIE Standard Observer.
At first glance it may seem that the problem with the
wideband filters is insufficient wavelength discrimination.
The middle row of the example attempts to solve
that problem by using three narrowband filters. The
narrowband set solves one problem, but creates
another: Many monochromatic sources “fall between”
the filters. Here, the orange source reports an RGB
triple of [0, 0, 0], identical to the result of scanning
black.
Although my example is contrived, the problem is not.
Ultimately, the test of whether a camera or scanner is
successful is whether it reports distinct RGB triples if
and only if human vision sees two SPDs as being
CHAPTER 21 THE CIE SYSTEM OF COLORIMETRY 215
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