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Multi-stage automatic focusing method according to time-frequency domain catched by iris picture

An iris image and auto-focus technology, applied in the field of biometric identification, can solve the problems of unfavorable quasi-focus search and search direction judgment, and achieve the effects of high sensitivity to texture details, high robustness, and good monotonicity

Inactive Publication Date: 2007-01-10
NANJING UNIV
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AI Technical Summary

Problems solved by technology

Therefore, using the commonly used image sharpness evaluation method is not conducive to quasi-focus search and search direction judgment in a large range

Method used

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  • Multi-stage automatic focusing method according to time-frequency domain catched by iris picture
  • Multi-stage automatic focusing method according to time-frequency domain catched by iris picture
  • Multi-stage automatic focusing method according to time-frequency domain catched by iris picture

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Embodiment Construction

[0020] The present invention will be described in detail below in conjunction with the accompanying drawings.

[0021] A kind of multi-stage iris auto-focus method process combining frequency domain and time domain according to the present invention, see figure 1 . In the specific implementation process, the telephoto lens is connected with the CCD sensor, and the captured image is input into the PC through the image acquisition card for sharpness evaluation; the PC sends an action command to the stepping motor according to the evaluation result, and drives the zoom mechanism to move. The frame rate of the image acquisition card is 30, and the image resolution is 320×240. It consists of the following steps:

[0022] (1) Coarse focus throughout

[0023] The requirements for the ideal full-range evaluation method are: the lateral range of the peak should be large, so that real-time search can be carried out in a larger range; the fluctuation of the curve on both sides of the ...

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Abstract

The present invention discloses multistage irides image automatical focusing method combining frequency domain and time domain, method key being the image definition. It contains judging aerodynamic center position through image resolution evaluation function, driving executing structure adjusting optical system focus point to form one automatical focusing closed loop control system. Said Automatical focusing process includes two stages: rough focusing stage adopting downsampling FFT low frequency coefficient evaluation procedure determining search direction and focus point adjacent region; fine focusing stage adopting global gradient sum evaluation procedure accuracy positioning focus point. Optimized control strategy uses improved blindman hill climbing method hill climbing method to execute stepwise image evaluation procedure, adopting different scouting speed further raising said invention real time property. Said invention overcomes tradition single evaluation procedure shortage, capable of realizing rapid and precise focusing.

Description

technical field [0001] The invention relates to iris recognition and image acquisition in the field of biological feature recognition, and relates to an iris image autofocus method used in a non-invasive iris autofocus recognition system. Background technique [0002] With the rapid development of the information society, the application fields of biometric identification technology are becoming more and more extensive. The use of human biometrics to identify personal identities will become an important innovation in the information industry in the next few years. Among them, iris recognition is a technology that is easy to operate, high in precision and has broad market prospects in current biometric technology. In the iris image acquisition system, the autofocus method is used to adjust the optical system components so that the reflected light of the human eye passes through the optical system to form a clear focused image on the image sensor (such as a CCD image sensor) ...

Claims

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Application Information

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IPC IPC(8): G03B13/36G06K9/00
Inventor 都思丹李杨李华王荣昌罗浩薛卫叶迎宪赵康僆朱欢欢严惠琼刘红星
Owner NANJING UNIV
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