Method and apparatus for adjusting contrast of image

• US 20070216956A1
• Filed: 11/02/2006
• Published: 09/20/2007
• Est. Priority Date: 03/16/2006
• Status: Active Grant

• Current Assignee: Quanta Computer
• Original Assignee: Quanta Computer
• Inventors: Hsu, Yung-Sheng, Hsieh, Tung-Lin, Huang, Yu-Wen, Chen, Hsu-Hung
• Granted Patent: US 7,973,860 B2
• Time in Patent Office: Days
• US Class Current: 358/3.210
• CPC Class Codes: G06T 5/40 using histogram techniques
• CPC Class Codes: G06T 5/70 Denoising; Smoothing
• CPC Class Codes: G06T 5/92 based on global image properties

Abstract

This invention relates to an apparatus for processing an input image including M input pixels. Each of the M input pixels respectively has an input gray scale. The apparatus includes a gain generating module, a contrast enhancing module, and a Gamma adjusting module. The gain generating module generates a contrast gain and a minimum input gray scale in accordance with the input gray scales of the M input pixels. The contrast enhancing module adjusts the input gray scales in accordance with the contrast gain and the minimum input gray scale, to generate an intermediate image. The intermediate image includes M intermediate pixels, and each of the M intermediate pixels respectively has an intermediate gray scale. The Gamma adjusting module adjusts the intermediate gray scales lower than a first threshold in accordance with the contrast gain and outputs the adjusted intermediate image as an output image.

Claims

1. An apparatus for processing a target video frame comprised in a video stream comprising M input pixels, M being a positive integer, each of the M input pixels respectively having an input gray scale, said apparatus comprising:

a gain generating module for generating, in accordance with the input gray scales of the M input pixels, a contrast gain and a minimum input gray scale;

a contrast enhancing module for adjusting, in accordance with the contrast gain and the minimum input gray scale, the input gray scales of the M input pixels to generate an intermediate image comprising M intermediate pixels which each respectively has an intermediate gray scale; and

a Gamma adjusting module for adjusting, in accordance with the contrast gain, the intermediate gray scales lower than a first threshold and for outputting the adjusted intermediate image as an output image.

2. The apparatus of claim 1, wherein the gain generating module comprises:

a statistical unit for selecting a maximum input gray scale and the minimum input gray scale from the input gray scales by a statistical approach; and

a generating unit for generating, in accordance with the maximum input gray scale and the minimum input gray scale, the contrast gain.

3. The apparatus of claim 1, wherein the gain generating module comprises:

a smoothing unit for performing a smoothing calculation on the M input gray scales;

a statistical unit for selecting a maximum input gray scale and the minimum input gray scale from the smoothed input gray scales by a statistical approach; and

a generating unit for generating, in accordance with the maximum input gray scale and the minimum input gray scale, the contrast gain.

4. The apparatus of claim 1, wherein in the video stream, the target video frame is adjacent to N adjacent video frames, N being a positive integer, and the gain generating module comprises:

a statistical unit for selecting an initial maximum input gray scale and an initial minimum input gray scale from the input gray scales by a statistical approach;

a generating unit for generating, in accordance with the initial maximum input gray scale and the initial minimum input gray scale, an initial gain; and

an averaging unit for averaging the initial gain and N adjacent gains associated with the N adjacent video frames to generate the contrast gain, the averaging unit further being used for averaging the initial minimum input gray scale and N adjacent minimum gray scales associated with the N adjacent video frames to generate the minimum input gray scale.

5. The apparatus of claim 1, wherein in the video stream, the target video frame is adjacent to N adjacent video frames, N being a positive integer, and the gain generating module comprises:

a smoothing unit for performing a smoothing calculation on the M input gray scales;

a statistical unit for selecting an initial maximum input gray scale and an initial minimum input gray scale from the smoothed input gray scales by a statistical approach;

a generating unit for generating, in accordance with the initial maximum input gray scale and the initial minimum input gray scale, an initial contrast; and

an averaging unit for averaging the initial gain and N adjacent gains associated with the N adjacent video frames to generate the contrast gain, the averaging unit further being used for averaging the initial minimum input gray scale and N adjacent minimum gray scales associated with the N adjacent video frames to generate the minimum input gray scale.

6. The apparatus of claim 1, wherein the Gamma adjusting module comprises:

a selecting unit for selecting, in accordance with the contrast gain, a Gamma curve from a look-up table; and

an adjusting unit for adjusting, in accordance with the Gamma curve, the intermediate gray scales lower than the first threshold.

7. The apparatus of claim 6, wherein the Gamma curve comprises a first sub-curve and a second sub-curve, the adjusting unit adjusts, in accordance with the first sub-curve, the intermediate gray scales lower than a second threshold, and the adjusting unit further adjusts, in accordance with the second sub-curve, the intermediate gray scales between the first threshold and the second threshold, the second threshold being smaller than the first threshold.

8. An apparatus for processing an input image comprising M input pixels, M being a positive integer, each of the M input pixels respectively having an input gray scale, said apparatus comprising:

a gain generating module for generating, in accordance with the input gray scales of the M input pixels, a contrast gain;

a contrast enhancing module for adjusting, in accordance with the contrast gain, the input gray scales of the M input pixels to generate an intermediate image comprising M intermediate pixels which each respectively has an intermediate gray scale; and

a Gamma adjusting module for adjusting, in accordance with the contrast gain, the intermediate gray scales lower than a first threshold and for outputting the adjusted intermediate image as an output image.

9. A method for processing a target video frame comprised in a video stream comprising M input pixels, M being a positive integer, each of the M input pixels respectively having an input gray scale, said method comprising:

(a) generating a contrast gain and a minimum input gray scale in accordance with the input gray scales of the M input pixels;

(b) generating an intermediate image comprising M intermediate pixels which each respectively has an intermediate gray scale in accordance with the contrast gain and the minimum input gray scale; and

(c) adjusting the intermediate gray scales lower than a first threshold and outputting the adjusted intermediate image as an output image in accordance with the contrast gain;

10. The method of claim 9, wherein the step (a) comprises the sub-steps of:

(a1) selecting a maximum input gray scale and the minimum input gray scale from the input gray scales by a statistical approach; and

(a2) generating the contrast gain in accordance with the maximum input gray scale and the minimum input gray scale.

11. The method of claim 9, wherein the step (a) comprises the sub-steps of:

(a1) performing a smoothing calculation on the M input gray scales;

(a2) selecting a maximum input gray scale and the minimum input gray scale from the smoothed input gray scales by a statistical approach; and

(a3) generating the contrast gain in accordance with the maximum input gray scale and the minimum input gray scale.

12. The method of claim 9, wherein in the video stream, the target video frame is adjacent to N adjacent video frames, N being a positive integer, and the step (a) comprises the sub-steps of:

(a1) selecting an initial maximum input gray scale and an initial minimum input gray scale from the input gray scales by a statistical approach;

(a2) generating an initial gain in accordance with the initial maximum input gray scale and the initial minimum input gray scale; and

(a3) averaging the initial gain and N adjacent gains associated with the N adjacent video frames to generate the contrast gain, and further averaging the initial minimum input gray scale and N adjacent minimum gray scales associated with the N adjacent video frames to generate the minimum input gray scale.

13. The method of claim 9, wherein in the video stream, the target video frame is adjacent to N adjacent video frames, N being a positive integer, and the step (a) comprises the sub-steps of:

(a1) performing a smoothing calculation on the M input gray scales;

(a2) selecting an initial maximum input gray scale and an initial minimum input gray scale from the smoothed input gray scales by a statistical approach;

(a3) generating an initial gain in accordance with the initial maximum input gray scale and the initial minimum input gray scale; and

(a4) averaging the initial gain and N adjacent gains associated with the N adjacent video frames to generate the contrast gain, and further averaging the initial minimum input gray scale and N adjacent minimum gray scales associated with the N adjacent video frames to generate the minimum input gray scale.

14. The method of claim 9, wherein the step (c) comprises the sub-steps of:

(c1) selecting a Gamma curve from a look-up table in accordance with the contrast gain; and

(c2) adjusting the intermediate gray scales lower than the first threshold in accordance with the Gamma curve.

15. The method of claim 14, wherein the Gamma curve comprises a first sub-curve and a second sub-curve, the step (c2) adjusts the intermediate gray scales lower than a second threshold in accordance with the first sub-curve, the step (c2) further adjusts the intermediate gray scales between the first threshold and the second threshold in accordance with the second sub-curve, and the second threshold is smaller than the first threshold.

16. A method for processing an input image comprising M input pixels, M being a positive integer, each of the M input pixels respectively having an input gray scale, said method comprising the steps of:

generating a contrast gain in accordance with the input gray scales of the M input pixels;

generating an intermediate image comprising M intermediate pixels which each respectively has an intermediate gray scale, in accordance with the contrast gain; and

adjusting the intermediate gray scales lower than a first threshold and outputting the adjusted intermediate image as an output image in accordance with the contrast gain.