We characterize scenes as being very flat if their scene brightness range is
of the order of only ten to one. A very contrasty scene's SBR is about 1000
to one.
(c) When we look at a photographic negative we see the many
different tones, from the darkest to the lightest, in random locations
throughout the image. If we arrange these tones in order from the lightest
to the darkest, we have an arrangement that is much easier to evaluate. The
Sensitometric Step Wedge represents this very arrangement, simulating all
possible SBRs. The lightest to the darkest steps of this step wedge differ
by 1,024 to one, enough to represent any possible SBR found in nature.
(2) Importance of sensitometric monitoring.
As previously stated,
sensitometry may be employed to measure the photographic chemistry's ability
to consistently reproduce predictable processing results.
Sensitometric
monitoring of color processing will not only give you a graphic illustration
of what your process is doing, it will prewarn you of potential problems and
assist you in correcting those problems.
Process monitoring can also be
looked upon as insurance because it prevents the loss of film due to
processing errors.
Process monitoring saves time, materials, and possible
loss of the mission.
(a) The key word in the monitoring of any system is repeatability.
Each time film is processed the results should be the same. To monitor your
process and ensure this repeatability, the first problem encountered is the
chemistry.
When you have the chemistry properly mixed and verified with
correct pH and SG measurements, you will need to process the first control
strip. Pre-exposed control strips (containing 1,024 to 1 SBR densities) may
be purchased from film manufacturers for this purpose.
(b) The first pre-exposed control strip or the processed reference
strip from the manufacturer represents the standard or reference to which
all subsequent control strips will be compared.
The color dye densities
(yellow, magenta, and cyan) from each corresponding emulsion layer are
measured separately with a transmission densitometer. The density readings
are then listed on a Color Process Record Form using either a red, green, or
blue color pencil according to the emulsion's light sensitivity.
2-20
SS0514
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