Method and apparatus for performing image enhancement

• US 5,949,918 A
• Filed: 08/18/1997
• Issued: 09/07/1999
• Est. Priority Date: 05/21/1997
• Status: Expired due to Term

• Current Assignee: RPX Corporation
• Original Assignee: Sarnoff Corporation (SRI International, Inc.)
• Inventors: McCaffrey, Nathaniel Joseph
• Primary Examiner(s): Lee, Thomas D.
• Assistant Examiner(s): BRINICH, STEPHEN M
• Application Number:
  US08/912,660
• Time in Patent Office: 750 Days
• Field of Search: 358/518, 358/520, 358/447, 382/254, 382/274, 382/271, 382/162, 382/167
• US Class Current: 382/274
• CPC Class Codes: G06T 2207/10016 Video; Image sequence
• CPC Class Codes: G06T 5/92 based on global image properties
• CPC Class Codes: H04N 1/4072 dependent on the contents of the original
• CPC Class Codes: H04N 5/20 Circuitry for controlling amplitude response

Abstract

A method and apparatus for processing an image stream to enhance a parameter of the image. The image stream comprises a plurality of picture elements (pixels), each of which include a characteristic related to the image parameter to be enhanced. The pixels are processed according to a controllable function to produce a processed image stream. A statistical distribution of the pixel characteristic of interest is determined, optimized and used to generate control information to modify the operation of the controllable function.

Claims

1. A method for processing an image stream to enhance a parameter of an image, said image comprising a plurality of picture elements (pixels), each of said pixels including a characteristic related to said image parameter, said method comprising the steps of:

(a) processing each of said pixels of said image stream according to a controllable function to produce a processed image stream;

(b) determining a statistical distribution of said pixel characteristic in said image stream, said statistical distribution representative of said parameter of said image;

(c) generating at least one function coefficient for optimizing said determined statistical distribution; and

(d) modifying said controllable function using said at least one function coefficient;

wherein

said controllable function is a remapping function and said at least one function coefficient is a lookup value.

2. The method of claim 1, wherein:

said image parameter is a luminance parameter, said pixel characteristic is an intensity level, and one of N possible intensity levels are associated with each of said pixels, and wherein;

said step of determining a distribution of said intensity levels comprises the step of counting, for a predetermined number of pixels, the number of pixels having each of said N possible intensity levels.

3. The method of claim 1 wherein said step of generating one or more function coefficients comprises the steps of:

sequentially adding to an accumulator a determined pixel count representative of the number of pixels having an intensity level from a first intensity level to said Nth intensity level; and

generating a function coefficient during each sequential addition by dividing the accumulated total by N.

4. A method for processing an image stream to enhance a parameter of an image, said image comprising a plurality of picture elements (pixels), each of said pixels including a characteristic related to said image parameter, said method comprising the steps of:

(a) processing each of said pixels of said image stream according to a controllable function to produce a processed image stream;

(b) determining a statistical distribution of said pixel characteristic in said image stream, said statistical distribution representative of said parameter of said image;

(c) generating at least one function coefficient for optimizing said determined statistical distribution; and

(d) modifying said controllable function using said at least one function coefficient;

wherein

said step of determining further comprises the steps of;

identifying pixels within said image that represent motion within the image; and

emphasizing the statistical significance of said pixel characteristics associated with said identified pixels.

5. A method for processing an image stream to enhance a parameter of an image, said image comprising a plurality of picture elements (pixels), each of said pixels including a characteristic related to said image parameter, said method comprising the steps of:

(a) processing each of said pixels of said image stream according to a controllable function to produce a processed image stream;

(b) determining a statistical distribution of said pixel characteristic in said image stream, said statistical distribution representative of said parameter of said image;

(c) generating at least one function coefficient for optimizing said determined statistical distribution; and

(d) modifying said controllable function using said at least one function coefficient;

wherein

said image parameter is a color parameter, said pixel characteristic is a color saturation level, and one of N possible color saturation levels are associated with each of said pixels, and wherein;

said step of determining a distribution of said color saturation levels comprises the step of counting, for a predetermined number of pixels, the number of pixels having each of said N possible color saturation levels.

6. The method of claim 5 wherein said step of generating one or more function coefficients comprises the steps of:

sequentially adding to an accumulator a determined pixel count representative of the number of pixels having an color saturation level from a first color saturation level to said Nth color saturation level; and

generating a function coefficient during each sequential addition by dividing the accumulated total by N.

7. The method of claim 5, wherein said controllable function is a remapping function and said at least one function coefficient is a lookup value.

8. The method of claim 5, wherein said step of determining further comprises the steps of:

identifying pixels within said image that represent motion within the image; and

emphasizing the statistical significance of said pixel characteristics associated with said identified pixels.

9. Apparatus processing an image stream to enhance a parameter of an image, said image comprising a plurality of picture elements (pixels), each of said pixels including a characteristic related to said image parameter, said apparatus comprising:

a pixel processor, receiving said image stream at an input and producing a processed image stream at an output, said pixel processor processing each received pixel of said image stream according to a controllable function;

a controller, coupled to said pixel processor and receiving said digital video signal at an input, said controller determining a statistical distribution of said pixel characteristic in said image stream and generating at least one function coefficient for optimizing said determined statistical distribution;

a motion detector, receiving said image stream at an input and producing an indicium of detected motion at an output, said motion detector identifying pixels within said image stream that represent motion within the image; and

a priority adjuster, coupled to said motion detector, for emphasizing the statistical significance of said pixel characteristics associated with said pixels within said image stream that represent motion within the image;

said pixel processor, in response to a control signal from said controller, modifying said controllable function using said at least one function coefficient.

10. The apparatus of claim 9, wherein

said image parameter and said pixel characteristic comprises either a luminance parameter and a respective intensity level, or a color parameter and a respective color saturation level;

one of N possible intensity levels or color saturation levels are associated with each of said pixels, and

said controller determines said distribution of said intensity levels or color saturation levels by counting, for a predetermined number of pixels, the number of pixels having each of said N possible intensity levels or color saturation levels.

11. The apparatus of claim 9, wherein said controller generates said one or more function coefficients by sequentially adding to an accumulator a determined pixel count representative of the number of pixels having a color saturation level from a first color saturation level to said Nth color saturation level, said controller generating a function coefficient during each sequential addition by dividing the accumulated total by N.

12. Apparatus processing an image stream to enhance a parameter of an image, said image comprising a plurality of picture elements (pixels), each of said pixels including a characteristic related to said image parameter, said apparatus comprising:

a pixel processor, receiving said image stream at an input and producing a processed image stream at an output, said pixel processor processing each received pixel of said image stream according to a controllable function; and

a controller, coupled to said pixel processor and receiving said digital video signal at an input, said controller determining a statistical distribution of said pixel characteristic in said image stream and generating at least one function coefficient for optimizing said determined statistical distribution;

said pixel processor, in response to a control signal from said controller, modifying said controllable function using said at least one function coefficient;

wherein said controllable function is a remapping function and said at least one function coefficient is a lookup value.

13. The apparatus of claim 12, further comprising:

a motion detector, receiving said image stream at an input and producing an indicium of detected motion at an output, said motion detector identifying pixels within said image stream that represent motion within the image; and

a priority adjuster, coupled to said motion detector, for emphasizing the statistical significance of said pixel characteristics associated with said pixels within said image stream that represent motion within the image.

14. The apparatus of claim 12, wherein said controller generates said one or more function coefficients by sequentially adding to an accumulator a determined pixel count representative of the number of pixels having a color saturation level from a first color saturation level to said Nth color saturation level, said controller generating a function coefficient during each sequential addition by dividing the accumulated total by N.

15. Apparatus for contrast-enhancing a digital video signal, said digital video signal comprising a sequence of picture elements (pixels), each of said pixels having an associated intensity level, said apparatus comprising:

a pixel processor, receiving said digital video signal at an input, and in response to each received pixel providing at an output a pixel having an intensity level derived from a lookup table, said lookup table having one element representing each of N possible intensity levels; and

a controller, coupled to said pixel processor and receiving said digital video signal at an input, said controller statistically determining a luminance profile of said digital video signal, adjusting said statistically determined luminance profile to provide an enhanced contrast luminance profile, and coupling said enhanced contrast luminance profile to said pixel processor;

said pixel processor selectively adjusting said lookup table elements in response to said enhanced contrast luminance profile;

said controller statistically determining said luminance profile of said digital video signal by counting the number of M pixels having each of said N possible intensity levels; and

said controller generates said one or more function coefficients by sequentially adding to an accumulator a determined pixel count representative of the number of pixels having an intensity level from a first intensity level to said Nth intensity level, said controller generating a function coefficient during each sequential addition by dividing the accumulated total by N.

16. The apparatus of claim 15, further comprising:

a motion detector, coupled to said controller, for determining which pixels represent motion in the image;

said pixel processor emphasizing the statistical significance of said pixel characteristics associated with pixels representing motion in the image.