Real-time digital color processor for a programmable high-resolution CCD camera with high colorimetric accuracy

摘要

In the course of ESPRIT II project No. 2103 (MASCOT) a high performance color CCD camera was developed. It is based on a 1K $MUL 1K frame-transfer CCD imager whose pixels are covered with an optimized dielectric filter stripe pattern. A microscanning optical unit is employed to displace the image, with a reproducibility of 1/200th of the pixel period, for programmable color image acquisition with a maximum resolution of 3K $MUL 3K color (RGB, XYZ, etc.) pixels. The CCD's output is immediately digitized to 10 bits using an in-house developed ADC subsystem whose performance of 67 dB S/N at 20 MHz is ideal for this application. The data is stored in one of three fast framestores. The raw data is read out simultaneously from these three framestores at a data rate of 30 MBytes per second and processed, fully digitally, in a special color processor. After non-linear transformations to compensate for detector non-linearities, color matrixing is carried out using one set of 16 matrix parameters which have been optimized for different illumination conditions and color temperatures. They also enable the selection of the type of output data to be generated e.g., RGB for specific phosphors, CIE XYZ tristimulus values, etc. After matrixing, a non-linear table-lookup can be used to introduce gamma correction or other calibration functions. The color processor produces 8- bit color pixels at a rate of 20 MBytes per second, writing these data directly into an 8 MBytes commercial framestore plugged into a PC/AT.