Signal processor for an imaging sensor system

• US 5,083,204 A
• Filed: 10/01/1984
• Issued: 01/21/1992
• Est. Priority Date: 10/01/1984
• Status: Expired due to Term

• Current Assignee: Raytheon Company (Rtx Corporation)
• Original Assignee: Hughes Aircraft Company (Rtx Corporation)
• Inventors: Heard, James L., Scanlan, Larry A., Andrews, Roland L., Berwin, Ted W.
• Primary Examiner(s): Buczinski, Stephen C.
• Application Number:
  US06/656,382
• Time in Patent Office: 2,668 Days
• Field of Search: 358/113, 358/166, 250/332, 340/744
• US Class Current: 348/164
• CPC Class Codes: H04N 25/21 for transforming thermal infrared radiation into image signals
• CPC Class Codes: H04N 25/673 by using reference sources
• CPC Class Codes: H04N 5/208 for compensating for attenuation of high frequency components, e.g. crispening, aperture distortion correction
• CPC Class Codes: H04N 5/33 Transforming infrared radiation cameras or camera modules for generating image signals from infrared radiation H04N23/20; circuitry of SSIS for transforming infrared radiation into image signals H04N25/20

Abstract

A signal processor for use with an imaging sensor system that provides enhanced video imagery. The signal processor may be coupled to a FLIR system, for example, which comprises a plurality of detectors that are scanned across an image scene and reference temperature source during separate portions of each scan cycle. The signal processor comprises an input processor coupled to the imaging sensor system which processes analog signals derived from each of the plurality of detectors. The input processor normalizes the analog signals relative to one another during the active portion of the scan cycle based upon stored data derived from a predetermined sensor responsivity calibration procedure. This normalization function equalizes the gains associated with all channels of the sensor system. The input processor also restores the DC levels of each of the sensor channels to respective DC values related to the reference temperature source during the inactive portion of the scan cycle. This function is performed during the calibration procedure and while the system is in operation. The input processor digitizes the signals which are applied to a scan converter. The scan converter stores the digitized signals and converts the stored signals into signals which are compatible with a video monitor employed to view the image. An output processor is coupled to the scan converter that is employed to process signals in a manner which permits software-controlled digitized image enhancement thereof, and which converts the enhanced signals into analog video output signals compatible with the video monitor.

Claims

1. A signal processor for use with an imaging sensor system that comprises a plurality of detectors which are scanned across an image scene during a first portion of a scan cycle and scanned across a reference temperature source during a second portion of said scan cycle, said signal processor providing video output signals to a video monitor which are representative of said image scene, said signal processor comprising:

input processor means coupled to said imaging sensor system for processing analog signals derived from each of said plurality of detectors in order to equalize the gains of said analog signals relative to one another another during said first portion of said scan cycle based upon stored gain correction signals derived from a predetermined sensor responsivity calibration procedure, for processing said analog signals in order to restore the DC levels of signals derived from each of said detectors to DC values related to said reference temperature source during said second portion of said scan cycle, and for processing the equalized and DC restored signals to provide digitized first output signals from said input processor means, said input processor means including means for generating automatic responsivity equalization factors and DC restoration values including circuit means for correcting errors in said equalization factors resulting from adjustment of said restoration values and for correcting errors in said restoration values resulting from adjustment of said equalization factors;

scan converter means coupled to said input processor means for storing digitized first output signals and processing the stored digitized signals to provide digitized second output signals which are compatible with said video monitor; and

output processor means coupled to said scan converter means for processing said second digitized output signals in a manner which permits software-controlled digitized image enhancement thereof, and for converting the enhanced second digitized output signals into analog video signals compatible with said video monitor.

2. The signal processor of claim 1 wherein said input processor means comprises:

analog to digital conversion means for converting applied analog signals into said digitized first output signals;

summing means for combining said analog signals, said DC restoration signals and said gain correction signals and applying the combined signals to said analog to digital converter; and

computer processor means coupled to said analog to digital conversion means and said summing means for computing said DC level correction signals and for controlling combining of the analog signals, gain correction signals and DC level correction signals in a predetermined manner to provide signals which are digitized by said analog to digital conversion means.

3. The signal processor of claim 2 wherein said computer processor means comprises:

a non-volatile memory for storing gain correction constants derived from said calibration procedure;

first memory means coupled to said summing means for storing said DC restoration signals prior to their application to said summing means;

second memory means coupled to said summing means for storing said gain correction signals prior to their application to said summing means;

a computer processor coupled to said non-volative memory, said first and second memory means and said analog to digital converter for computing said DC restoration signals and storing them in said first memory means, for loading said gain correction signals from said non-volative memory into said second memory means, and for controlling the processing of said analog signals, and said gain correction signals in order to combine said signals in said analog to digital converter.

4. The signal processor of claim 3 wherein said first memory means comprises:

a clamping voltage reference circuit coupled to said analog to digital converter for processing output signals derived therefrom in order to provide fixed voltage reference signals for the computation of said DC restoration signals; and

a counter circuit for processing to said voltage reference signals in order to provide incrementing and decrementing signals to said first memory means which adjust and normalize said DC restoration signals relative to said fixed voltage reference during each scan cycle.

5. The signal processor of claim 4 wherein said first and second memory means further comprise:

first and second random access memories;

first and second digital to analog converters coupled between said first and second random access memories, respectively, for converting digital signals stored in said memories into analog signals compatible with said analog to digital converter.

6. The signal processor of claims 1, 2, 3, 4, or 5 wherein said scan conversion means comprises:

a scan converter for storing said digitized first output signals; and

interpolation means coupled to said scan converter for converting the digitized first output signals into said digitized second output signals which are compatible with said video monitor.

7. The signal processor of claim 6 wherein said output processor means comprises:

look-up table generation means for computing and storing a look-up table comprising image enhancement correction signals;

digital to analog conversion means coupled to said look-up table generation means for converting signals received from said scan converter means into analog video output signals compatible with said video monitor;

aperture correction means coupled to said digital to analog converter for processing the enhanced signals derived from said look-up table generation means in order to enhance the modulation transfer function of said system; and

computer processor means coupled to said look-up table generation means for computing the signals comprising said look-up table.

8. The signal processor of claim 7 wherein said look-up table generation means comprises:

histogram generation means for generating a histogram of the number of occurrences of said first output signals at each intensity level associated with said sensor;

a look-up table memory for storing said image enhancement signals;

said computer processor means computing said image enhancement correction signals utilizing said histogram and storing said computed signals in said look-up table memory.

9. A signal processor for use with an imaging sensor system that comprises a plurality of detectors which are scanned across an image scene during a first portion of a scan cycle and scanned across a reference temperature source during a second portion of said scan cycle, said signal processor providing video output signals to a video monitor which are representative of said image scene, said signal processor comprising:

input processor means coupled to said imaging sensor system for processing analog signals derived from each of said plurality of detectors in order to equalize the gains of said analog signals relative to one another during said first portion of said scan cycle based upon stored gain correction signals derived from a predetermined sensor responsivity calibration procedure, for processing said analog signals in order to restore the DC levels of signals derived from each of said detectors to DC values related to said reference temperature source during said second portion of said scan cycle, and for processing the equalized and DC restored signals to provide digitized first output signals from said input processor means, said input processor means including means for generating automatic responsivity equalization factors and DC restoration values including circuit means for correcting errors in said equalization factors resulting from adjustment of said restoration values, and for correcting errors in said restoration values resulting from adjustment of said equalization factors.

10. A signal processor for use with an imaging sensor system that comprises a plurality of detectors which are scanned across an image scene during a first portion of a scan cycle and scanned across a reference temperature source during a second portion of said scan cycle, said signal processor providing video output signals to a video monitor which are representative of said image scene, said signal processor comprising:

input processor means coupled to said imaging sensor system for processing analog signals derived from each of said plurality of detectors in order to equalize the gains of said analog signals relative to one another during said first portion of said scan cycle based upon stored gain correction signals derived from a predetermined sensor responsivity calibration procedure, for processing said analog signals in order to restore the DC levels of signals derived from each of said detectors to DC values related to said reference temperature source during said second portion of said scan cycle, and for processing the equalized and DC restored signals to provide digitized first output signals from said input processor means, said input processor means including means for generating automatic responsivity equalization factors and DC restoration values including circuit means for correcting errors in said equalization factors resulting from adjustment of said restoration values, and for correcting errors in said restoration values resulting from adjustment of said equalization factors; and

means for converting and processing said digitized first output signals from input processor means into analog video output signals compatible with said video monitor.

11. A signal processor for use with an imaging sensor system that comprises a plurality of detectors which are scanned across an image scene during a first portion of a scan cycle and scanned across a reference temperature source during a second portion of said scan cycle, said signal processor providing video output signals to a video monitor which are representative of said image scene, said signal processor comprising:

input processor means coupled to said imaging sensor system for processing analog signals derived from each of said plurality of detectors in order to equalize gains of said analog signals relative to one another during said first portion of said scan cycle based upon stored gain correction signals derived from a predetermined sensor responsivity calibration procedure, for processing said analog signals in order to restore the DC levels of signals derived from each of said detectors to DC values related to said reference temperature source during said second portion of said scan cycle, and for processing the equalized and DC restored signals to provide digitized first output signals from said input processor means, said input processor means including means for generating accurate automatic responsivity equalization factors and accurate DC restoration values including means for substantially eliminating offsets in restoration values resulting from adjustment of equalization factors, and vice-versa; and

means for converting and processing said digitized first output signals from said input processor means into analog video output signals compatible with said video monitor.