METHOD AND APPARATUS FOR PROCESSING IMAGE

• US 20110013048A1
• Filed: 09/03/2010
• Published: 01/20/2011
• Est. Priority Date: 05/13/2008
• Status: Active Grant

• Current Assignee: Honor Device Company Limited
• Original Assignee: Huawei Device Company Limited (Huawei Investment & Holding Co., Ltd.)
• Inventors: Long, Yanbo, Wei, Xiaoxia
• Granted Patent: US 8,334,925 B2
• Time in Patent Office: Days
• US Class Current: 348/234
• CPC Class Codes: G06T 2207/10016 Video; Image sequence
• CPC Class Codes: G06T 2207/20008 Globally adaptive
• CPC Class Codes: G06T 5/009 Global, i.e. based on properties of the image as a whole applied in cameras using an electronic image sensor H04N23/80, H04N23/70
• CPC Class Codes: G06T 5/40 using histogram techniques
• CPC Class Codes: G06T 5/92 based on global image properties
• CPC Class Codes: H04N 23/71 Circuitry for evaluating the brightness variation
• CPC Class Codes: H04N 23/76 by influencing the image signals

Abstract

A method and an apparatus for processing images are disclosed. The method includes: generating an image histogram of an image to be processed; judging whether the image to be processed requires backlight compensation according to the image histogram; if the image to be processed requires backlight compensation, determining a first luminance boundary value A used for deciding whether to perform backlight compensation and a second luminance boundary value C used for deciding whether to perform positive or negative backlight compensation; and performing backlight compensation for the image to be processed according to the first luminance boundary value A and the second luminance boundary value C. The method is simple and universally applicable. After backlight compensation, the contrast of the image is high, and the image is free from background overexposure and image layering. The image photographed in a backlight environment is processed properly.

Claims

1. A method for processing an image, comprising:

generating an image histogram of an image to be processed;

judging whether the image to be processed requires backlight compensation according to the image histogram;

if the image to be processed requires the backlight compensation, determining a first luminance boundary value A used for deciding whether to perform the backlight compensation and a second luminance boundary value C used for deciding whether to perform positive or negative backlight compensation; and

performing backlight compensation for the image to be processed according to the first luminance boundary value A and the second luminance boundary value C.

2. The method for processing an image according to claim 1, further comprising:

detecting whether a scenario of the image to be processed as a current-frame image is different from a scenario of a previous-frame image if the image to be processed requires the backlight compensation.

3. The method for processing an image according to claim 2, further comprising:

if detecting that the scenario of the image to be processed as the current-frame image is the same as the scenario of the previous-frame image, using a first luminance boundary value and a second luminance boundary value of the previous-frame image as a first luminance boundary value and a second luminance boundary value of the current-frame image respectively; and

if detecting that the scenario of the image to be processed as the current-frame image is different from the scenario of the previous-frame image, determining the first luminance boundary value A used for deciding whether to perform the backlight compensation and the second luminance boundary value C used for deciding whether to perform the positive or negative backlight compensation again according to the image histogram of the image to be processed in the current-frame image.

4. The method for processing an image according to claim 1, wherein judging whether the image to be processed requires the backlight compensation includes:

obtaining a luminance level L₁ of a pixel point corresponding to a crest value of a highest peak with a maximum crest luminance and a luminance level L₂ of a pixel point corresponding to a crest value of a second highest peak whose crest luminance level is lower than an average luminance of the image histogram; and

determining that the image to be processed requires the backlight compensation if L₁−

L₂>

K, wherein K is a fixed luminance difference and K>

0.

5. The method for processing an image according to claim 4, further comprising:

performing convolution and operation for a normalized image histogram through a gate sequence, and finding crests of the highest peak and the second highest peak.

6. The method for processing an image according to claim 1, wherein the first luminance boundary value A used for deciding whether to perform the backlight compensation comprises:

using the luminance level greater than luminance of any pixel point of a foreground target in the image to be processed as the first luminance boundary value A.

7. The method for processing an image according to claim 1, wherein the first luminance boundary value A used for deciding whether to perform the backlight compensation comprises:

determining the luminance level is greater than luminance of any pixel point of a foreground target in the image to be processed, and the luminance level is less than luminance of a pixel point corresponding to a crest value of a highest peak in the image histogram of the image to be processed; and

using the luminance level as the first luminance boundary value A.

8. The method for processing an image according to claim 1, wherein the first luminance boundary value A used for deciding whether to perform the backlight compensation comprises:

selecting an x-coordinate corresponding to a minimum value point adjacent to a crest value of a highest peak in the image histogram as the first luminance boundary A, wherein the x-coordinate corresponding to the minimum value point is less than an x-coordinate corresponding to the crest value of the highest peak.

9. The method for processing an image according to claim 1, wherein the second luminance boundary value C used for deciding whether to perform the positive or negative backlight compensation comprises:

determining the luminance level less than luminance of any pixel point of a foreground target in the image to be processed as the second luminance boundary value C.

10. The method for processing an image according to claim 9, wherein the luminance level less than the luminance of any pixel point of the foreground target in the image to be processed is determined as the second luminance boundary value C comprises:

determining the second luminance boundary value C as L₂−

Δ

L, wherein Δ

L is a fixed luminance level offset.

11. The method for processing an image according to claim 1, wherein the performing backlight compensation for the image to be processed according to the first luminance boundary value A and the second luminance boundary value C comprises:

performing backlight compensation for pixel points whose luminance level falls within [0, C] and (C, A] in the image to be processed.

12. The method for processing an image according to claim 11, wherein the backlight compensation for the pixel points whose luminance level falls within [0, C] and (C, A] in the image to be processed comprises:

obtaining a first compensation function ƒ

₁(x) for performing the backlight compensation for the pixel points whose luminance level falls within [0, C] in the image to be processed;

obtaining a second compensation function ƒ

₂(x) for performing the backlight compensation for the pixel points whose luminance level falls within (C, A] in the image to be processed;

performing the backlight compensation for the pixel points whose luminance level falls within [0, C] according to the first compensation function ƒ

₂(x); and

performing the backlight compensation for the pixel points whose luminance level falls within (C, A] according to the second compensation function ƒ

₂(x).

13. The method for processing an image according to claim 12, wherein:

the first compensation function ƒ

₁(x) and the second compensation function ƒ

₂(x) are power functions.

14. The method for processing an image according to claim 12, wherein:

the first compensation function ƒ

₁(x) and the second compensation function ƒ

₂(x) are high-order functions.

15. The method for processing an image according to claim 12, wherein the first compensation function and the second compensation function are obtained in the following way:

determining values of parameters other than non-independent variables in the first compensation function ƒ

₁(x) and the second compensation function ƒ

₂(x) according to conditions of ƒ

₁(C)=C, ƒ

₂(A)=A, and ƒ

₁(C)=ƒ

₂(C).

16. The method for processing an image according to claim 15, wherein:

the first compensation function is;

17. An apparatus for processing an image, comprising:

an image histogram generating unit, adapted to generate an image histogram of an image to be processed;

a backlight compensation judging unit, adapted to judge whether the image to be processed requires backlight compensation according to the image histogram of the image to be processed;

a backlight compensation parameter generating unit, adapted to generate a first luminance boundary value A and a second luminance boundary value C for the backlight compensation if the backlight compensation judging unit determines that the image to be processed requires the backlight compensation; and

a backlight compensation unit, adapted to perform the backlight compensation for the image to be processed according to the first luminance boundary value A and the second luminance boundary value C generated by the backlight compensation parameter generating unit.

18. The apparatus for processing an image according to claim 17, wherein the backlight compensation parameter generating unit comprises:

a first boundary value generating unit, connected to the backlight compensation judging unit and the backlight compensation unit, and adapted to generate the first luminance boundary value A and the second luminance boundary value C according to the image histogram; and

a first function generating unit, connected to the first boundary value generating unit and the backlight compensation unit, and adapted to generate a first compensation function and a second compensation function according to the first luminance boundary value A and the second luminance boundary value C generated by the first boundary value generating unit, wherein the first compensation function and the second compensation function are designed to perform the backlight compensation for the image to be processed.

19. The apparatus for processing an image according to claim 17, further comprising:

a scenario change detecting unit, connected to the backlight compensation parameter generating unit, and adapted to detect whether a scenario of the image to be processed as a current-frame image is different from a scenario of a previous-frame image, and adapted to perform functions of the backlight compensation parameter generating unit if detecting that the scenario is different.

20. The apparatus for processing an image according to claim 19, wherein the backlight compensation parameter generating unit comprises:

a storing unit, adapted to store backlight compensation parameters of an image before the current-frame image, namely, a first luminance boundary value and a second luminance boundary value applied in processing the image before the current-frame image;

a second boundary value generating unit, connected to the storing unit, the scenario change detecting unit, the backlight compensation judging unit, and the backlight compensation unit, and adapted to generate a first luminance boundary value and a second luminance boundary value of the current-frame image according to a judgment result of the backlight compensation judging unit and a detection result of the scenario change detecting unit, or determine a first luminance boundary value and a second luminance boundary value of the previous-frame image as the first luminance boundary value and the second luminance boundary value of the current-frame image respectively; and

a second function generating unit, connected to the second boundary value generating unit and the backlight compensation unit, and adapted to generate a first compensation function and a second compensation function according to the first luminance boundary value and the second luminance boundary value generated by the second boundary value generating unit, wherein the first compensation function and the second compensation function are designed to perform the backlight compensation for the image to be processed.