By the use of high performance solid-state infrared emitting diodes, matched infrared detectors, and a single chip 8-bit microprocessor, an in-process infrared densitometer has been designed and constructed. The device is capable of recording the build-up of optical transmission density on an exposed film sample as it develops, with no effect on the normal development process. The most novel feature of this system is a special development chamber with eleven built-in infrared densitometers. These densitometers are located as to read every other step of a standard Kodak #2 step-tablet exposure, and to allow the passage of developer across the film sample. As an example, every other step of a 21-step exposure can be measured to produce a series of eleven density readings in approximately 22 milliseconds. These measurements can be repeated from once every second to once per minute at any time during the development process. The microprocessor that controls the infrared densitometer has memory capacity to store the data required to generate 187 complete D-Log exposure curves. At the completion of processing, the density readings recorded earlier are available for user viewing on a large seven segment digital display system, or can be reproduced on a line printer. D-Log exposure curves obtained from the device are in good agreement with curves obtained by conventional means. The device has a useful range of 0 to 3.00 density units with an accuracy of +/- .02 density units
