Algorithm for calculating high accuracy image slopes

• US 9,218,641 B1
• Filed: 06/19/2012
• Issued: 12/22/2015
• Est. Priority Date: 06/19/2012
• Status: Active Grant

• Current Assignee: Harris Corporation (L3Harris Technologies, Inc.)
• Original Assignee: Exelis Incorporated (L3Harris Technologies, Inc.)
• Inventors: Ellis, Kenneth K.
• Primary Examiner(s): Vaughn, Jr., William C
• Assistant Examiner(s): PEREZ FUENTES, LUIS M
• Application Number:
  US13/526,799
• Time in Patent Office: 1,281 Days
• Field of Search: 382/181, 348/144
• US Class Current: 1/1
• CPC Class Codes: G01C 11/02 Picture taking arrangements specially adapted for photogrammetry or photographic surveying, e.g. controlling overlapping of pictures
• CPC Class Codes: G01C 11/025 by scanning the object
• CPC Class Codes: G06T 3/08 Projecting images onto non-planar surfaces, e.g. geodetic screens
• CPC Class Codes: G06T 3/4007 based on interpolation, e.g. bilinear interpolation image demosaicing G06T3/4015; edge-driven or edge-based scaling G06T3/403
• CPC Class Codes: H04N 7/005 using at least one opto-electrical conversion device

Abstract

A method of determining slope of pixel intensities in an image includes the following steps: (a) receiving, from an imaging device, input pixel samples of a region of interest; (b) forming an impulse response function (IPR) for use in resampling the input pixel samples into output pixel intensities; and (c) calculating a derivative of the IPR. Also included is the step of convolving the derivative of the IPR with the input pixel samples to determine the slope of the output pixel intensities in the region of interest. In addition, the input pixel samples are generated in a first coordinate system by the imaging device, and the output pixel intensities are generated in a second coordinate system.

Claims

1. A method of determining slope of pixel intensities in an image, comprising the steps of:

receiving, from an imaging device, input pixel samples of a region of interest;

resampling the received input pixel sample into output pixel intensities using an impulse response function (IPR);

calculating a derivative of the IPR; and

convolving the derivative of the IPR with the input pixel samples to determine the slope of the output pixel intensities in the region of interest wherein the step of convolving is defined by the following equation;

s′

(x)=r′

(x)®

h(x)®

u(x)

 

where;

s(x) is the output pixel intensities in the region of interest,

s′

(x) is the slope of the output pixel intensities in the region of interest,

h(x) is an impulse response of the imaging device,

u(x) is scene intensity, r(x) is the IPR, r′

(x) is the derivative of the IPR.

2. The method of claim 1 wherein the input pixel samples are generated in a first coordinate system by the imaging device, and the output pixel intensities are generated in a second coordinate system.

3. The method of claim 1 wherein the input pixel samples are formed along a first axis in a first coordinate system, and the output pixel intensities are formed along a second axis in a second coordinate system;

and

the step of convolving includes the following sub-steps;

placing the first axis and the second axis along a common axis;

centering the derivative of the IPR at a point along the second axis;

obtaining samples of the derivative of the IPR at points along the first axis;

multiplying each sample of the derivative of the IPR by a corresponding input pixel sample at corresponding points along the first axis; and

summing results of the multiplying step.

4. The method of claim 1 wherein the imaging device includes

at least one of a night vision infrared camera,

a visible camera, or an ultraviolet camera, and

the method includes the step of:

providing the output pixel intensities to at least one of a display or a storage device.

5. The method of claim 1 wherein the region of interest is an edge in the image.

6. The method of claim 5 wherein the edge includes at least one of a geographic feature, a pattern in a database of patterns, or a segment of an image.

7. The method of claim 1 wherein the region of interest is a knife-edge target in the image, and the knife-edge target is used for calculating an optical transfer function (OTF) of the image.

8. A method of determining slope of a region of interest in an image, the method comprising the steps of:

receiving input pixel samples of the region of interest from an imager, the input pixel samples imaged in a first coordinate system;

forming a first function representing the input pixel samples, defined along a first axis in the first coordinate system;

resampling the input pixel samples into output pixel intensities using an impulse response function (IPR) in which the output pixel intensities are defined along a second axis in a second coordinate system;

calculating a derivative of the IPR, defined as a second function along the second axis; and

convolving the first function with the second function to determine the slope of output pixel intensities in the region of interest, wherein

the first function is defined as f(x), and

the second function is defined as g′

(x), and

the convolving is defined by the following equation;

f(x)×

g′

(x).

9. The method of claim 8 wherein the input pixel samples are generated by the imager viewing a scene in an imager-centered coordinate system, defined as the first coordinate system;

and

the output pixel intensities are generated for display by a user viewing the scene in an earth-centered coordinate system, defined as the second coordinate system.

10. The method of claim 8 wherein convolving includes the sub-steps of:

placing the first axis and the second axis along a common axis;

centering the second function at a point along the second axis;

obtaining samples of the second function at points along the first axis;

multiplying each sample of the second function by a corresponding input pixel sample at corresponding points along the first axis; and

summing results of the multiplying step.

11. The method of claim 8 wherein the slope of the output pixel intensities defines an edge in the region of interest of the image.

12. The method of claim 8 wherein the slope of the output pixel intensities in the region of interest defines a knife-edge target in the image.

13. A system of determining slope of pixel intensities in an image comprising:

an imager for viewing a region of interest in a scene and obtaining input pixel samples in a first coordinate system,

a display for viewing the scene in a second coordinate system, and

a processor configured to;

resample the input pixel samples into output pixel intensities in the second coordinate system using an impulse response function;

calculate a derivative of the impulse response function; and

calculate the slope of the output pixel intensities in the second coordinate system by convolving the derivative of the impulse response function with the input pixel samples, wherein the single operation is expressed by the following equation;

s′

(x)=r′

(x)®

h(x)®

u(x)

 

where;

s(x) is the output pixel intensities in the region of interest,

s′

(x) is the slope of the output pixel intensities in the region of interest,

h(x) is an impulse response of the imaging device,

u(x) is scene intensity,

r(x) is the impulse response function,

r′

(x) is the derivative of the impulse response function.

14. The system of claim 13 wherein the processor is further configured to resample the input pixels samples from the first coordinate system to the second coordinate system and calculate the slope of the output pixel intensities using a single operation.

15. The system of claim 13 wherein the imager is disposed in an airborne platform, and the scene includes a geographic location on the Earth.

16. The system of claim 15 wherein

the first coordinate system is centered about the airborne platform;

and

the second coordinate system is centered about the Earth.

17. The system of claim 13, wherein the processor is further configured to:

calculate an optical transfer function (OTF) of the image based on the determined slope of the output pixel intensities.