# US 8,571,403 B2 · Autofocus system

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- Number: US 8,571,403 B2
- Document ID: US8571403B2
- Status: Granted
- Kind: B2
- Application number: 13/491,409
- Filed: 2012-06-07
- Published: 2012-09-27
- Granted: 2013-10-29
- Earliest claimed: 2010-05-14
- Assignees: National Taiwan University
- Applicants: Tung-Chan Tsai; Homer H. Chen
- Inventors: Tung-Chan Tsai; Homer H. Chen
- Web page: https://patentgrep.com/patent/US8571403B2

## CPC

- G03B 13/36: Autofocus systems
- H04N 23/673: {based on contrast or high frequency components of image signals, e.g. hill climbing method}
- G03B: APPARATUS OR ARRANGEMENTS FOR TAKING PHOTOGRAPHS OR FOR PROJECTING OR VIEWING THEM; APPARATUS OR ARRANGEMENTS EMPLOYING ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ACCESSORIES THEREFOR (optical parts of such apparatus G02B; photosensitive materials or processes for photographic purposes G03C; apparatus for processing exposed photographic materials G03D)
- H04N: PICTORIAL COMMUNICATION, e.g. TELEVISION

## Abstract

In an autofocus system, a focus measurement unit receives an image, and accordingly generates an associated focus value. A focus transform unit receives and then transforms the focus value provided by the focus measurement unit, therefore generating an associated transformed focus value. An in-focus position estimation unit obtains an in-focus position, in an analytical manner, according to some transformed focus values and some associated lens positions.

## Claims

### Claim 1

An autofocus system, comprising:
a focus measurement unit configured to receive an image and accordingly generate an associated focus value;
a focus transform unit configured to receive the focus value provided by the focus measurement unit and then transform the focus value, thereby generating an associated transformed focus value; and
an in-focus position estimation unit configured to obtain an in-focus position, in an analytical manner, according to a plurality of the transformed focus values and a plurality of associated lens positions.

### Claim 2 (depends on 1)

The system of claim 1, further comprising:
a transform construction unit configured to receive a focus profile provided by the focus measurement unit, and transform the focus profile to generate a transformed focus profile, which is then provided to the focus transform unit to perform transformation on the focus value.

### Claim 3 (depends on 2)

The system of claim 2, wherein the transformed focus profile is described by an analytical mathematical expression.

### Claim 4 (depends on 2)

The system of claim 2, wherein the transformed focus profile is expressed by a numerical table that keeps a record of the focus values and the associated transformed focus values.

### Claim 5 (depends on 4)

The system of claim 4, wherein, the numerical table is stored in a memory device of an image capture device.

### Claim 6 (depends on 1)

The system of claim 1, further comprising:
a driving unit configured to move a lens to a lens position to capture an associated image, according to which the focus measurement unit generates the associated focus value.

### Claim 7 (depends on 1)

The system of claim 1 is adapted to a still camera.

### Claim 8 (depends on 1)

The system of claim 1 is adapted to a video camera.

### Claim 9 (depends on 1)

The system of claim 1, wherein, the focus measurement unit comprises a high-pass filter.

### Claim 10

An autofocus method, comprising:
receiving an image and accordingly generating an associated focus value;
receiving the focus value and then transforming the focus value, thereby generating an associated transformed focus value; and
obtaining an in-focus position, in an analytical manner, according to a plurality of the transformed focus values and a plurality of associated lens positions.

### Claim 11 (depends on 10)

The method of claim 10, further comprising:
receiving a focus profile by collecting the focus values and the associated lens positions, and transforming the focus profile to generate a transformed focus profile, which is then used to perform transformation on the focus value.

### Claim 12 (depends on 11)

The method of claim 11, wherein the transformed focus profile is described by an analytical mathematical expression.

### Claim 13 (depends on 11)

The method of claim 11, wherein the transformed focus profile is expressed by a numerical table that keeps a record of the focus values and the associated transformed focus values.

### Claim 14 (depends on 13)

The method of claim 13, wherein the numerical table is stored in a memory device of an image capture device.

### Claim 15 (depends on 10)

The method of claim 10, further comprising:
driving to move a lens to a lens position to capture an associated image, according to which the associated focus value is generated.

### Claim 16 (depends on 10)

The method of claim 10 is adapted to a still camera.

### Claim 17 (depends on 10)

The method of claim 10 is adapted to a video camera.

### Claim 18 (depends on 10)

The method of claim 10, wherein the step of generating the focus value is performed by high-pass filtering.