Television – Pseudo color – Multispectral to color conversion
Reexamination Certificate
1994-12-23
2001-09-18
Le, Vu (Department: 2613)
Television
Pseudo color
Multispectral to color conversion
C348S266000, C348S273000, C250S338100
Reexamination Certificate
active
06292212
ABSTRACT:
FIELD OF THE INVENTION
The invention relates generally to the field of photography, and in particular to multi-spectral photography. More specifically, the invention relates to an electronic color infrared camera.
BACKGROUND OF THE INVENTION
Infrared photography with false color materials offers potential value in a wide range of fields. Applications include medical, reconnaissance, geographical surveys, resource management (roads, buildings, and utilities), law enforcement, environmental and agricultural assessment, art authenticity analysis, forgery investigation, and pictorial applications.
Traditionally, false color images are captured photographically with traditional photographic cameras and infrared-sensitive film. The film products available on the market today are: KODAK Aerochrome Infrared Film 2443; and KODAK Aerochrome Infrared NP Film SO-134. These products are sensitive to light in the green (500-600 nm), red (600-700 nm), and infrared (700-900 nm) portions of the electromagnetic spectrum.
It has been proposed to employ 3 monochromatic video cameras, each having a spectral filter (e.g. green red and infrared centered on 550 nm, 650 nm and 850 nm respectively) and aimed at the same scene to produce a false color digital image signal. See the article “An airborne multi-spectral video/radiometer remote sensing system for natural resource monitoring” by C.M.U. Neale, Thirteenth Biennial Workshop on Color Aerial Photography, Orlando Fla., May 6-9, 1992.
More recently, infrared information has been captured with a panchromatic-infrared electronic camera. In this method, a filter wheel is placed before a panchromatic and infrared sensitive charge coupled device (CCD) array in an electronic camera. An image is acquired by sequentially exposing the CCD through a series of filters, which represent the desired spectral bands of the imagery. When imagery is acquired electronically, it can be easily downloaded from the camera into a computer, where it can be analyzed and displayed. Currently, Eastman Kodak's Professional Digital Camera System (DCS) Model 420 IR operates by this sequential filter wheel technique.
Although these technological options exist to capture infrared-sensitive imagery, they are not without problems. Today's infrared-sensitive films are consumable media and require wet photographic processing. Detailed analysis of the resulting images requires photographic scanning for input into geographic analysis computer software or digital image processing routines, causing a considerable delay in preparing and analyzing time-sensitive data. The infrared imaging systems employing video (as opposed to digital) imaging technology suffer from the problems of low resolution, poor response to relative image/camera motion, and the complexity resulting from the use of a number of cameras.
The state-of-the-art digital electronic technology described above requires a dedicated infrared electronic camera, with a moving filter-wheel assembly, as embodied in the DCS Model 420 IR camera system, with the Kodak Color Filter Wheel Assembly. Because the filter wheel requires sequential capture of the imagery bands (it acquires three bands in 40 seconds), the camera can only be used for still photography applications (i.e. where there is no relative movement between the camera and the scene), and is therefore not useful for aerial photography. Also, the filter wheel increases the complexity of the camera system thereby decreasing the mechanical reliability of the system.
Alternatively, an infrared sensitive electronic camera employing beam splitters and three linear detectors is shown in U.S. Pat. No. 4,170,987, issued Oct. 16, 1979 to Anselmo et al. This approach trades off the high cost and mechanical complexity of the filter wheel for the higher cost of three separate image detectors.
From the foregoing it is seen that there is a need for an improved digital electronic infrared camera to capture near infrared imagery.
SUMMARY OF THE INVENTION
The present invention is directed to overcoming one or more of the problems set forth above. According to one aspect of the invention, an infrared digital electronic camera includes a solid state color image sensor having an array of image sensing elements and an array of color filter elements including infrared color filter elements arranged over the image sensing elements for producing a color image signal. A signal processing circuit processes the color image signals from the image sensor to produce a false color image signal.
According to a further aspect of the invention, a digital electronic camera includes a solid state color image sensor having an array of image sensing elements and an array of red, green and blue color filter elements for producing a color image signal. A package for mounting the solid state color image sensor has a window that blocks blue light and passes infrared light. A signal processing circuit (preferably a programmed microprocessor, or alternatively a custom integrated circuit) processes the color image signals from the image sensor to produce a false color image signal by subtracting an infrared signal from the red and green signals produced by the image sensor. This aspect of the invention has the special advantage of being easily and cost effectively produced in a process that normally produces true color digital image cameras, by merely replacing the window in the package for mounting the image sensor and adding appropriate signal processing, thereby realizing economies of scale in the manufacturing process.
According to a still further aspect of the invention, a digital electronic camera is provided, having: a solid state color image sensor with an array of image sensing elements and an array of color filter elements arranged over the image sensing elements for producing a color image signal. A filter mechanism having an infrared filter portion and a color filter portion is moveable between a first position wherein the infrared filter portion is located to filter light reaching the image sensor, and a second position wherein the color filter portion is located to filter light reaching said image sensor. A signal processing circuit responds to the filter being in the second position for processing the color image signals from the image sensor to produce a false color image signal. This aspect of the invention has the special advantage of being readily convertible between an infrared sensing electronic camera to a true color electronic camera. In a preferred embodiment of this aspect of the invention, the image sensor has red, green and blue sensitive elements, the color filter portion of the filter mechanism is a yellow filter, and the signal processing circuit removes an infrared component from the green and red signal when the yellow filter is over the image sensor. The signal processing circuit causes the green component of the sensed image to be displayed as blue, the red component to be displayed as green, and the infrared to be displayed as red.
The infrared electronic camera of the present invention is advantageous in that all three color bands of information are collected concurrently without the need for a mechanical filter wheel assembly; nor does the camera need multiple cameras, multiple image sensors, or means for image registration between the images from multiple cameras or multiple image sensors. The infrared camera of the present invention is useful for motion or rapid capture applications.
These and other aspects, objects, features and advantages of the present invention will be more clearly understood and appreciated from a review of the following detailed description of the preferred embodiments and appended claims, and by reference to the accompanying drawings.
REFERENCES:
patent: 3566015 (1971-02-01), Watanabe
patent: 3748471 (1973-07-01), Ross et al.
patent: 3806633 (1974-04-01), Coleman
patent: 3935589 (1976-01-01), Ohta
patent: 3971065 (1976-07-01), Bayer
patent: 4016597 (1977-04-01), Dillon et al.
patent: 4170987 (1979-10-01), Anselmo et al.
patent: 4403247 (1983-09-
Holden Carl L.
Schrader Mark E.
Vogel Richard M.
Zigadlo Joseph P.
Close Thomas H.
Eastman Kodak Company
Le Vu
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