Method and system for forming an image with enhanced contrast and/or reduced noise

• US 7,796,829 B2
• Filed: 12/10/2008
• Issued: 09/14/2010
• Est. Priority Date: 12/10/2008
• Status: Expired due to Fees

• Current Assignee: United States Of America As Represented By The Secretary Of The Army (Government of the United States of America), The United States of America As Represented By The Secretary of Agriculture
• Original Assignee: The United States Of America As Represented By The Secretary Of The Army
• Inventors: Sichina, Jeffrey P., Nguyen, Lam Huy
• Primary Examiner(s): Tarcza; Thomas H
• Assistant Examiner(s): Brainard; Timothy A
• Application Number:
  US12/331,888
• Publication Number:
  US 20100141508A1
• Time in Patent Office: 643 Days
• Field of Search: 382/260, 342/26.R
• US Class Current: 382/260
• CPC Class Codes: G01S 13/9017 with time domain processing of the SAR signals in azimuth G01S13/9005 takes precedence
• CPC Class Codes: G01S 13/9089 SAR having an irregular aperture

Abstract

A method and system for generating images from projection data; a preferred embodiment comprising inputting projection data from at least one receiving element; generating a first aperture or array of data points containing positional and signal data; arbitrarily and/or randomly removing data points from the first array to form a series of subarrays comprising different sets of data points; generating preliminary images from the subarrays; comparing the corresponding image pixels from two preliminary images to determine for each pixel location the lesser or equal pixel values; forming a merged image from the lesser or equal pixel values; and repeating the comparison of corresponding image pixels of another preliminary image to the merged image to determine the lesser or equal pixel values until a merged image of the desired quality is obtained. A preferred embodiment of the system may comprise at least one processor, comparator and/or image generator.

Claims

1. A method for generating images from projection data comprising:

scanning an area using at least one data receiving element to obtain first values representing combined positional and recorded data;

each of said first values forming a point in an array of k data points;

the first point in the array representing the positional information and the recorded data obtained during the first increment;

the k^th data point in the array representing the combined positional information and recorded data obtained by the at least one data receiving element during the k^th increment;

where k is a number greater than 1;

removing approximately twenty to fifty percent of the data points from the array;

forming a first preliminary bit-mapped image using the reduced array of data points;

forming a second array by removing approximately twenty to fifty percent of the data points from the array;

forming a second preliminary bit-mapped image using the second array of data points;

generating a combined image by comparing each bit-mapped location of the first and second preliminary images and removing any pixel value which is greater in value at respective bit mapped locations to form a merged image of lesser or equal value pixels;

subsequently repeating the steps of removing approximately twenty to fifty percent of the data points from the array to form a reduced array, and forming a subsequent preliminary image from the reduced array, and generating a merged image by comparing the pixel values of the subsequent preliminary image to the preceding merged image, eliminating the greater values, and forming a subsequent combined image from the resulting lesser or equal pixel values;

whereby the steps are repeated over a series of iterations until the desired image resolution is obtained.

2. The method of claim 1 wherein the at least one data receiving element is a radar receiving element and each first value represents a radar return signal obtained by a radar receiving element located at a position represented by the positional data, and wherein the positional data comprises the coordinates of the radar receiving element.

3. The method of claim 1 wherein the array of k data points represents radar data obtained by an array of k radar receivers, each row of data being derived from a separate radar receiver, and wherein columns may be formed in the array comprising data from a different time interval in which data is received by each of the k radar receivers.

4. The method of claim 1 wherein the step of removing twenty to fifty percent of the data points from the array to form a reduced array comprises removing the same predetermined percentage of data points each the time with the selection of the data points subject to removal being computer generated.

5. The method of claim 1 wherein the step of removing twenty to fifty percent of the data points from the array to form a reduced array comprises removing a varying percentage of data points each the time with the selection of the data points subject to removal being random.

6. The method of claim 1 wherein each time the step of removing approximately twenty to fifty percent of the data points from the array comprises removing a predetermined percentage of data points each time from random locations within the array, such that each time the step is performed, substantially the same number of data points at substantially a different set of locations is removed.

7. The method of claim 1 wherein the formation of the bit-mapped image is accomplished using a Fourier transform technique.

8. The method of claim 1 wherein a target can be located by inputting data from two receiving elements, determining the respective angles from signals reflected from the target obtained by both receiving elements, and determining the target location based upon the angles at which the signals are reflected, the time at which the signal is received, and the positional information of the receiving elements.

9. The method of claim 1 wherein each data receiving element scans substantially the same area and three dimensional images are obtained using signal data from each receiving element that includes the magnitude of the signal, the angle from which the signal was derived, the time of receipt, and the positional information of the receiving element.

10. The method of claim 1 wherein the at least one data receiving element comprises an array of receiving elements that scan substantially the same area during a second time period, said second time period substantially overlaps the first time period, and wherein the step of forming a preliminary image comprises forming a preliminary image using a regenerative technique.

11. The method of claim 10 wherein each time the step of removing approximately twenty to fifty percent of the data points from the array comprises removing a predetermined percentage of data points each time from random locations within the array, such that each time the step is performed, substantially the same number of data points at substantially a different set of locations is removed.

12. The method of claim 1 wherein the image is developed from the image points using back projection.

13. The method of claim 1 wherein the electromagnetic signals used to generate the image are susceptible to internal and external noise sources, and when a transmitted electromagnetic signal encounters a physical element within the targeted area, the resulting image comprises at least one response lobe and side lobes from the physical element, and noise signals.

14. The method of claim 13 wherein the reduction of noise is achieved by reducing the level of the sidelobes and noise signals.

15. The method of claim 14 wherein the at least one data receiving element comprises multiple receiving elements and the reception of signals varying in intensity from different combinations of receiver elements and location changes results in variances in the sidelobes and noise signals while the at east one response lobe from the physical element remains substantially unchanged;

whereby the removal of the data points from each array and the generating of merged images using pixel values of lesser or equal values effectively diminish the effect of the sidelobes and noise signals in the resulting image.

16. A signal processing system for removing unwanted noise in the generation of an image using electromagnetic signals comprising:

at least one receiving element for receiving signal data at different positions 1 though k;

a processor for forming a first array of data points 1 though k;

each data point comprising positional information representing the location of the at least one receiving element and signal data received by the at least one receiving element;

the processor operating to remove a percentage of the data points from the first array in the range of approximately 20 to 50 percent to form a second array, and generate a first preliminary image from the second array;

the processor operating to randomly or arbitrarily remove a percentage of data points in the range of 20 to 50 percent from the first array to form a series of arrays, each array in the series generally containing a substantially different set of data points;

an image generator for generating preliminary images from each array in the series of arrays;

a comparator for comparing the pixel values at each bitmapped location for at least two preliminary images and outputting the lesser or equal pixel value for each respective bitmapped location;

the image generator operating to generate a merged image from the output of the comparator;

the comparator further operating to compare a series of preliminary images with a merged image iteratively;

each time outputting the lesser or equal pixel value for each respective bitmapped location to form a merged image and iteratively comparing another in the series of preliminary images with the merged image;

a display for displaying the merged image.

17. The system of claim 16 wherein the electromagnetic signals are radar signals and when a transmitted electromagnetic signal encounters a physical element within the targeted area, the resulting image comprises at least one response lobe and side lobes from the physical element, and noise signals, and wherein the comparator operates to reduce the noise by diminishing the effect of the sidelobes and noise signals.

18. The system of claim 17 wherein the image generator utilizes a back projection method and wherein the at least one data receiving element comprises an array of receiving elements that scan substantially the same area.

19. A method for generating images from projection data comprising:

inputting projection data from at least one receiving element;

generating a first array comprising data points containing positional and signal data received from the at least one receiving element;

arbitrarily removing data points from the first array to form a series of subarrays;

each subarray generally being composed of different sets of data points;

generating preliminary images from the subarrays;

comparing the corresponding bitmapped locations from two preliminary images to determine bitmapped locations to determine the lesser or equal pixel values;

forming a merged image from the lesser or equal pixel values;

comparing the corresponding bitmapped locations of another preliminary image to the merged image to determine the lesser or equal pixel values; and

forming a merged image from the lesser or equal pixel values;

repeating the comparing of corresponding bitmapped locations of another preliminary image to the last merged image to form a subsequent merged image until the desired image quality is obtained.

20. The method of claim 19 wherein the projection data is in the form of electromagnetic signals.