Method for controlling exposure time of high dynamic range image

• US 9,131,160 B2
• Filed: 11/06/2013
• Issued: 09/08/2015
• Est. Priority Date: 08/08/2013
• Status: Active Grant

• Current Assignee: Quanta Computer
• Original Assignee: Quanta Computer
• Inventors: Chen, Hsin-Yu, Lin, Keng-Sheng, Cheng, Chih-Chi, Li, Chung-Te, Yang, Wen-Chu
• Primary Examiner(s): Giles, Nicholas
• Assistant Examiner(s): Tissire, Abdelaaziz
• Application Number:
  US14/073,067
• Publication Number:
  US 20150042836A1
• Time in Patent Office: 671 Days
• US Class Current: 1/1
• CPC Class Codes: H04N 23/73 by influencing the exposure time
• CPC Class Codes: H04N 23/741 by increasing the dynamic range of the image compared to the dynamic range of the electronic image sensors
• CPC Class Codes: H04N 23/743 Bracketing, i.e. taking a series of images with varying exposure conditions
• CPC Class Codes: H04N 25/57 Control of the dynamic range
• CPC Class Codes: H04N 25/58 involving two or more exposures
• CPC Class Codes: H04N 25/589 with different integration times, e.g. short and long exposures

Abstract

A method for controlling an exposure duration of a high dynamic range image, including: consecutively generating a first high dynamic range image having a first exposure duration ratio and a second high dynamic range image having a second exposure duration ratio greater than the first exposure duration ratio; performing image quality evaluations on both the first high dynamic range image and the second high dynamic range image to obtain a first image quality and a second image quality, respectively; and determining whether the second image quality is better than the first image quality; if yes, generating a third high dynamic range image having a third exposure duration ratio greater than the second exposure duration ratio; if not, generating the third high dynamic range image having the first exposure duration ratio and setting the first exposure duration ration as the optimal exposure duration ratio.

Claims

1. A method for controlling exposure time of high dynamic range images, comprising steps of:

using an image sensor to respectively shoot a first long exposure time image and a first short exposure time image for being merged to generate a first high dynamic range image having a first exposure duration ratio, wherein the first exposure duration ratio is a ratio of an exposure duration of the first long exposure time image to an exposure duration of the first short exposure time image;

using the image sensor to respectively shoot a second long exposure time image and a second short exposure time image for being merged to generate a second high dynamic range image having a second exposure duration ratio after shooting the first long exposure time image and the first short exposure time image, wherein the second exposure duration ratio is a ratio of an exposure duration of the second long exposure time image to an exposure duration of the second short exposure time image, wherein the second exposure duration ratio is greater than the first exposure duration ratio;

performing an image quality evaluation for the first high dynamic range image to obtain a first image quality, and performing an image quality evaluation for the second high dynamic range image to obtain a second image quality; and

comparing the second image quality with the first image quality;

if the second image quality is superior to the first image quality, using a third exposure duration ratio to shoot a third high dynamic range image, wherein the third exposure duration ratio is greater than the second exposure duration ratio;

if the second image quality is not superior to the first image quality, using the first exposure duration ratio of the first high dynamic range image to shoot the third high dynamic range image and setting the first exposure duration ratio as an optimal exposure duration ratio.

2. The method of claim 1, wherein each exposure duration ratio corresponds to an exposure duration, and an average of the exposure durations of the long exposure time image and the short exposure time image is equal to the exposure duration.

3. The method of claim 2, wherein the evaluation process of the image quality comprises a formula to calculate entropy, the equation is

4. The method of claim 2, wherein the evaluation process of the image quality comprises a step of calculating a sum of edges, and the greater sum of edges represents the better quality of the corresponding image.

5. The method of claim 2, wherein the evaluation process of the image quality further comprises a step of computing the ratio of over-exposure to under-exposure.

6. The method of claim 2, further comprising following steps of:

using the optimal exposure duration ratio to shoot a fourth high dynamic range image and a fifth high dynamic range image;

performing the image quality evaluation for the fourth high dynamic range image to obtain a fourth image quality;

performing the image quality evaluation for the fifth high dynamic range image to obtain a fifth image quality;

judging whether the fifth image quality is the same as the fourth image quality;

maintaining the optimal exposure duration ratio to sustainably shoot high dynamic range images if the fifth image quality is equal to the fourth image quality; and

clearing the optimal exposure duration ratio and using an initial exposure duration ratio to restart searching for the optimal exposure duration ratio if the fifth image quality is not equal to the fourth image quality.

7. The method of claim 6, wherein the fifth image quality and the fourth image quality are defined to be equal if a difference between the fifth image quality and the fourth image quality is within the range of ±

5% or ±

10%.

8. The method of claim 7, wherein the exposure duration ratio is an integer within the range of 1 to 64.