Histogram equalization apparatus for contrast enhancement of moving image and method therefor

• US 6,259,472 B1
• Filed: 04/22/1998
• Issued: 07/10/2001
• Est. Priority Date: 06/20/1996
• Status: Expired due to Fees

• Current Assignee: Samsung Electronics Co. Ltd.
• Original Assignee: Samsung Electronics Co. Ltd.
• Inventors: Park, Yung-jun
• Primary Examiner(s): Kelley, Chris
• Assistant Examiner(s): An, Shawn S.
• Application Number:
  US08/973,968
• Time in Patent Office: 1,175 Days
• Field of Search: 348/28, 348/672, 382/168, 382/6, 382/274, 382/169, 382/171, 382/264, 358/111
• US Class Current: 348/28
• CPC Class Codes: G06T 5/40 using histogram techniques
• CPC Class Codes: G06T 5/92 based on global image properties

Abstract

A histogram equalization apparatus for contrast enhancement of a moving image includes a CDF calculator for counting the number of pixels having a gray level from the minimum to the maximum or less with respect to an input image in a frame unit to calculate a cumulative distribution function (CDF) value of each gray level, and a look-up table for updating histogram-equalized level corresponding to each gray level of the input moving image in a frame unit based on the CDF value of each gray level, and outputting a corresponding histogram-equalized level according to a level of the input moving image. Therefore, the histogram equalization apparatus can perform real-time histogram equalization on a moving image with a simple hardware, without using a frame memory, a probability density function (PDF) calculator and dividers for a cumulative density function (CDF) calculation.

Claims

1. A histogram equalization apparatus for a image expressed by a predetermined number of gray levels, comprising:

a calculator for counting the number of pixels having a gray level from the minimum to the maximum or less with respect to an input image in a screen unit to calculate cumulative distribution function (CDF) values of each gray level; and

a memory for updating histogram-equalized levels corresponding to each gray level of the input image in a screen unit based on the CDF value of each gray level of a previous screen unit, and outputting a corresponding histogram-equalized level according to a level of the input image;

wherein the calculator comprises;

a plurality of comparators for comparing whether the level of the input image is less than or equal to each gray level; and

a plurality of accumulators for accumulating each output of the plurality of comparators to output the CDF values of each gray level from the minimum to the maximum or less per one screen unit.

2. The histogram equalization apparatus of claim 1, wherein the screen unit is a frame.

3. The histogram equalization apparatus of claim 1, wherein each accumulator accumulates the output of each comparator whenever a clock signal is input, and outputs an accumulated value and simultaneously clears the accumulated value according to a frame synchronous signal.

6. The histogram equalization apparatus of claim 1, wherein the histogram-equalized levels stored in the memory are obtained by multiplying the CDF values of each gray level calculated by the calculator by the maximum gray level.

4. A histogram equalization apparatus for a image expressed by a predetermined number of gray levels, comprising:

a calculator for counting the number of pixels having a gray level from the minimum to the maximum or less with respect to an input image in a screen unit to calculate cumulative distribution function (CDF) values of each gray level; and

a memory for updating histogram-equalized levels corresponding to each gray level of the input image in a screen unit based on the CDF value of each gray level, and outputting a corresponding histogram-equalized level according to a level of the input image;

wherein the calculator comprises;

a plurality of comparators for comparing the level of the input image with each gray level; and

a plurality of accumulators for accumulating each output of the plurality of comparators to output the CDF values of each gray level from the minimum to the maximum or less per one screen unit, wherein each accumulator accumulates the output of each comparator whenever a clock signal is input, and outputs an accumulated value and simultaneously clears the accumulated value according to a frame synchronous signal, and wherein the clock signal is generated according to a system clock signal and an area control signal representing a CDF calculation area.

5. The histogram equalization apparatus of claim 4, wherein the number of total pixels of a CDF calculation area is equal to 2^m, where m is an integer.

7. The histogram equalization apparatus of claim 5 wherein the histogram-equalized levels stored in the memory are obtained by shifting the values of each gray level from the minimum to the maximum or less by the number (m) corresponding to the power of radix-2, and then multiplying each shifted result by the maximum gray level.

8. A histogram equalization method for a image expressed by a predetermined number of gray levels, comprising the steps of:

(a) counting the number of pixels having a gray level from the minimum to the maximum or less with respect to an input moving image in a screen unit to output a CDF value of each gray level; and

(b) multiplying the CDF value corresponding to the level of a previous unit of the input moving image by the maximum gray level to output a histogram-equalized level;

wherein the step (a) comprises the sub-steps of;

(a1) comparing whether the level of the input image is less than or equal to each gray level from the minimum to the maximum or less; and

(a2) accumulating compared results of the step (a1) in a screen unit to output all values from the number of pixels having a gray level from the minimum to the maximum or less per screen.

9. The histogram equalization method of claim 8 wherein the number of total pixels of a CDF calculation area is equal to 2^m, where m is an integer.

10. The histogram equalization method of claim 8 wherein the screen unit is a frame.

11. A histogram equalization method for a image expressed by a predetermined number of gray levels, comprising the steps of:

(a) counting the number of pixels having a gray level from the minimum to the maximum or less with respect to an input image in a screen unit to output a CDF value of each gray level; and

(b) multiplying the CDF value corresponding to the level of the input image by the maximum gray level to output a histogram-equalized level, wherein the number of total pixels of a CDF calculation area is equal to 2^m, where m is an integer, and wherein the histogram-equalized levels of the step (b) is obtained by shifting the values of each gray level from the minimum to the maximum or less by the number (m) corresponding to the power of radix-2, and then multiplying each shifted result by the maximum gray level.