Much of the material discussed previously about quality assurance is carried over to understand color quality assurance. However, color processing quality assurance is more critical than QA used for conventional black-and-white film, particularly because color balance must be considered.

As with black-and-white QA, color QA procedures begin with a series of controlled exposures, but on color film. These exposures are measured with a color densitometer and then the red, green, and blue densities are recorded on a graph. Control strips for color processing are produced by the manufacturer.

The materials used in color process monitoring are as follows:

Monitoring manuals

Control strips and reference strips

Color densitometer

Control charts

Processing records of mechanical and chemical variables

MONITORING MANUALS

Since the details of the monitoring procedure change with each color process, process-monitoring manuals, such as Kodak's Z-series, are necessary supplements to a color process-monitoring system. The monitoring manuals describe the process, the specific control strip to use, the steps to read, the calculation of reference values and control values, the specific plot patterns, and the plot-pattern interpretation.

CONTROL STRIPS

Control strips for color process monitoring are supplied by the manufacturer of the color light-sensitive material or process. The most common control strips used in Navy imaging facilities are Kodak process-control strips. Like black-and-white control strips, color control strips have a series of neutral-density steps. Process monitoring relies primarily on the measurement of densities of the steps.

It is important to measure the minimum density and, usually, two steps representing intermediate tones. Monitoring D-max is also desirable for color reversal film and paper. The relationship among the three color measurements of a step is used to monitor color balance. The difference in the readings from the two steps (HD-LD) provides measurements of red, green, and blue contrast.

Control strips must be stored at 0F (-18C) or lower to minimize color shifts. The strips are stabilized and given an expiration date, so they provide a reliable tool to monitor processes. The strips should be removed from the freezer, one at a time, as they are needed.

A number of control strips from each control-strip batch are processed by the manufacturer. One of the processed strips is included with each package of control strips. These processed strips are called reference strips. The reference strips provide a means for imaging facilities to determine a process standard in terms of densitometer readings.

By reading these reference strips and applying correction factors (supplied with the control strips) to specified steps, you can determine the initial reference, mean, or aim values.