A Foveon Sensor/Green-Pass Filter Technique for Direct Exposure of Traditional False Color Images

A direct exposure technique to simulate the vegetation red-magenta hues associated with the traditional Kodak Ektachrome Professional Infrared EIR film is proposed. The method uses the Foveon sensor in full spectrum mode as found in Sigma cameras in combination with green-pass filters to reproduce the red-magenta hues of healthy vegetation without resorting to multi-exposures or channel swaps as is the current norm in single sensor cameras. An array of commercially available green-pass filters are analyzed via spectrophotmetric, densitometric and colorimetric measurements. A calibration technique using color-compensating filters is presented such that any green-pass filter will transmit green wavelengths to a set norm and ensure repeatability. A color model for the Foveon/green-pass filter is developed using quantum efficiencies to explain the color effects observed. Color similarities in near-infrared, blue and black and differences in red and green compared with Kodak Ektachrome Infrared film are discussed. Aerial photography examples are discussed, and the technique is proposed as a more direct means of obtaining traditional false color infrared imagery for pictorial and scientific applications when using Foveon type commercially available digital cameras.