American Cinematographer - December 2006 - 129

Committee

meetings who hear anybody

say the word linear' now know whether
it's being misused, and that's a big

improvement. It's important that people
understand when they are dealing with
linear light and linear energy, when
'linear' actually means video gamma
and 'logarithmic' can mean pure loga¬
rithmic, film density as in printing
density or Status M, or quasi-log as in
the Viper camera."
Reisner: "The terms 'linear' and

logarithmic' have been used very casu¬
ally. When all imaging elements came

pretty significant, I thought. We've put a
lot of

emphasis on spectral radiometry."
Reisner: "In spectral radiometry,
you take light and break it up into little
bands by frequency, covering the whole
range of human vision, and measure the
strength of each band. The list of
strengths of light in each band is the
spectral measurement you get from
a
spectroradiometer. Trichromatic
systems that we use very commonly in
motion-picture and other imaging, like
CIE 1931, use just three 'primary' colors
of light, instead of keeping track of, say,

from and went to film emulsions with

72 bands. Because of the structure of

known characteristics and known

the human eye

photo¬
chemical processes, people were able
to get away with it. But with hybrid and
digital imaging chains, there is a lot of
opportunity to come in from one direc¬
tion and leave in another. That also

applies to color gamut. With all these
different representation issues, there is
a lot of room for error. But keeping track
of these issues has a big impact on the
results of the Dl and visual-effects

especially when work is
being done at multiple houses."
processes,

Demos: "For basic color encod¬

ing, there

was a lot of assuming about
the CIE1931 color system. We definitely

have raised

awareness

that it contains

potential weaknesses. It needs further
examination, and it might not be the
way to go. There was a sense that it
was a panacea because so much color
science is based

on

it.

"We've also been flagging some
things that come along, such as the fact
that CRT color displays are disappearing
and those are what we've been using as
a

reference that

we

trust. We started

testing other technologies - flat
panels, plasmas, various projectors and
other things. We uncovered all kinds of
issues there, and we also were able to

strongly measure why we trust the CRT.
The CRT had certain consistent proper¬
ties that our measurements helped us
characterize and

quantify that

the other devices

seem

least not have to the

none

of

to have or at

degree of the cath¬
tube. The CRT has many other
weaknesses, but its strengths affected
its use in color judgment. That was
ode ray

120 December 2006

and visual system, light
just three colors can cause a color
experience very like the full spectrum,
even though that trichromatic represen¬
tation is far from physical reality. Using
just three color primaries, you can do a
pretty good job of getting the responses
you want from the eye and brain.
"When you look at something
that is orange in the real world, you get
light at all the different frequencies. But
if you look at that on a movie screen
with either film or digital projection,
you're getting a highly simplified version
of those frequencies - just a combina¬
tion of the three primary color light
sources, which may not be so simple or
pure. But you can get about the same
perception of color.
at

"Different combinations of the

green and blue, into a spectrum, and the
CIE 1931 two-degree Standard Colorimet¬

ric Observer is

a way of doing that. But it's
only way. There also is a CIE 1964
10-degree Supplementary Standard

not the

Colorimetric Observer.
"We invited
radiometer

work. We studied the instrument itself
we

can

expect? How much accuracy is it provid¬
ing? That's been ongoing. If you take
multiple meters, all of which are suppos¬
edly calibrated, you find that there are
slight differences in the measurements.
We are using multiple meters and are
starting to use multiple brands of meters
as

well to learn

about this and

see

they are."
Reisner: "Our goals encompass
both basic scientific understanding and
helping the industry produce better
results more consistently and more effec¬
tively. But the ultimate goal of any of this
helping people understand and deal
correctly with linear and logarithmic
representations, or understanding the

-

characteristics of the CIE trichromatic

systems and how they affect our image
processing - is to enable movie makers

give audiences the intended experi¬
That's always the ultimate goal."

Light by Numbers
by Jay Holben

Supplemen¬

tary Standard Colorimetric Observer
were developed. Trichromatic systems
are very practical but they are not

perfect, for example different observers
may perceive different colors. Gary has
been one of the leading people in our
industry digging into if or in what cases
the known problems with the CIE
systems may have an effect in creating
and exhibiting motion pictures."
Demos: "You have to have
way to map

more

how consistent

ence.

Observer and the CIE 1964

so

understand how accurate and

precise a measurement of the radiometric
spectrum it provides. If we use a particu¬
lar instrument, what accuracy should we

to

Standard Colorimetric

Photo

and tell how
they calibrate their instruments, how they

orange

the CIE 1931

of the spectral

Research to present to us

three

primaries may represent an
that feels the same to the
viewer. Two independent spectra that
are perceived as the same color are
called metamers. Color matching exper¬
iments looking at those issues are how

one

manufacturers,

some

the three colors like red,

Behind the
Men lurked

scenes

of Children of

unassuming light-control
console that might be best described as a
dimmer board on steroids. During its
development, Chris Gilbertson's Light by
Numbers system was brought in for the
major sets on Children of Men and
several other features shot on stages in
England, including Charlie and the Choco¬
late Factory (see AC My '05) and Alexan¬
der (AC Nov. '04). The basis of the system
is a standard ETC Insight board, but
an
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