Autofocus searching method

• US 7,929,044 B2
• Filed: 12/12/2007
• Issued: 04/19/2011
• Est. Priority Date: 12/22/2006
• Status: Active Grant

• Current Assignee: Industrial Technology Research Institute
• Original Assignee: Industrial Technology Research Institute
• Inventors: Chen, Jin-Liang, Chang, Chung Chu, Tung, Chi Hong
• Primary Examiner(s): Ometz; David L
• Assistant Examiner(s): Le; Quang V
• Application Number:
  US11/955,215
• Publication Number:
  US 20080151097A1
• Time in Patent Office: 1,224 Days
• Field of Search: 348/345, 348/349, 348/353, 348/356, 396/82, 396/79
• US Class Current: 348/349
• CPC Class Codes: G02B 7/38 measured at different points on the optical axis , e.g. focussing on two or more planes and comparing image data
• CPC Class Codes: H04N 23/673 based on contrast or high frequency components of image signals, e.g. hill climbing method

Abstract

An autofocus searching method includes the following procedures. First, focus values of images, which are acquired during the movement of the object lens, are calculated, in which the focus value includes at least the intensity value of the image derived from the intensities of the pixels of the image. Next, focus searching is based on a first focus-searching step constant and a first focus-searching direction, in which the first focus-searching step constant is a function, e.g., the multiplication, of the focus value and a focus-searching step size. If the focus searching position moves across a peak of the focus values, it is then amended to be based on a second focus-searching direction and a second focus-searching step constant, in which the second focus-searching step constant is smaller than the first focus-searching step constant, and the second focus-searching direction is opposite to the first focus-searching direction.

Claims

1. An autofocus searching method, comprising:

calculating a focus value of an image according to each position of an object lens in the movement, wherein the focus value comprises at least an intensity value of the image;

performing focus searching based on a first focus-searching step constant and a first focus-searching direction, wherein the first focus-searching step constant is a value of a function of the focus value and a focus-searching step size, and the focus value is inversely proportional to the focus-searching step size; and

performing focus searching based on a second focus-searching direction and a second focus-searching step constant if a focus-searching position moves across a peak of the focus value, wherein the second focus-searching direction is opposite to the first focus-searching direction;

wherein the focus value further comprises at least a contrast value or a definition value of the image,

wherein the definition value of the image is calculated by means of a space differential operation of the image or a frequency domain analysis of the image,

wherein the space differential operation of the definition value of the image comprises;

(a) providing a mask including weight values and weight positions;

(b) multiplying the weight on the mask by a pixel value corresponding to the weight position on the image by convolution;

(c) after adding the multiplication results, moving the mask to the next operation position and performing the operation of the step (b); and

(d) repeating the steps (b) and (c), and adding all the operation results as the definition value of the image.

2. The autofocus searching method of claim 1, wherein the focus-searching step size gradually decreases during focus-searching.

3. The autofocus searching method of claim 1, wherein the second focus-searching step constant is smaller than the first focus-searching step constant.

4. The autofocus searching method of claim 1, wherein the focus value is a combination of the intensity value, a contrast value, and a definition value of the image.

5. The autofocus searching method of claim 1, wherein the function is a multiplication or a square root of the multiplication.

6. The autofocus searching method of claim 1, wherein if the focus-searching position is far away from the peak of the focus value, the intensity value of the image is used as the focus value.

7. The autofocus searching method of claim 1, wherein if the focus-searching position approaches the peak of the focus value, the focus value comprises at least the contrast value or the definition value of the image.

8. The autofocus searching method of claim 1, wherein the step of performing the focus searching based on a first focus-searching step constant and a first focus-searching direction comprises:

dividing the first focus-searching step constant by the focus value corresponding to a position where the object lens is located currently as a focus-searching step size for the next movement of the object lens.

9. The autofocus searching method of claim 1, further comprising:

presetting an initial focus value and an initial focus-searching step size; and

calculating a value of a function of the initial focus value and the initial focus-searching step size as an initial focus-searching step constant.

10. The autofocus searching method of claim 1, wherein the contrast value of the image is calculated through the pixel intensity distribution in the image.

11. The autofocus searching method of claim 10, wherein the calculation of the contrast value of the image comprises:

statistically calculating at least a part of the pixel value distribution of the image by means of a histogram; and

determining the contrast value of the image according to the size of the distribution of the histogram.

12. The autofocus searching method of claim 1, wherein the intensity value of the image is calculated through pixel intensity analysis of the image.

13. The autofocus searching method of claim 1, wherein the intensity value of the image is a maximal brightness value of pixels or an average brightness value of pixels of the image.

14. The autofocus searching method of claim 1, wherein the determination of the focus-searching position comprises:

selecting a plurality of neighboring focus values;

dividing a curve formed by the plurality of focus values into a forepart curve and a back part curve according to the first focus-searching direction, and calculating slopes of the forepart curve and the back part curve; and

indicating that a peak of the focus value is crossed over if the slope of the forepart curve is smaller than that of the back part curve and exceeds a threshold value.

15. The autofocus searching method of claim 14, wherein the number of the plurality of focus values is larger than or equal to 3.