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Applied Optics

Applied Optics


  • Editor: Joseph N. Mait
  • Vol. 51, Iss. 21 — Jul. 20, 2012
  • pp: 5216–5223

Wavelet power spectrum-based autofocusing algorithm for time delayed and integration charge coupled device space camera

Shuping Tao, Guang Jin, Xuyan Zhang, Hongsong Qu, and Yuan An  »View Author Affiliations

Applied Optics, Vol. 51, Issue 21, pp. 5216-5223 (2012)

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A novel autofocusing algorithm using the directional wavelet power spectrum is proposed for time delayed and integration charge coupled device (TDI CCD) space cameras, which overcomes the difficulty of focus measure for the real-time change of imaging scenes. Using the multiresolution and band-pass characteristics of wavelet transform to improve the power spectrum based on fast Fourier transform (FFT), the wavelet power spectrum is less sensitive to the variance of scenes. Moreover, the new focus measure can effectively eliminate the impact of image motion mismatching by the directional selection. We test the proposed method’s performance on synthetic images as well as a real ground experiment for one TDI CCD prototype camera, and compare it with the focus measure based on the existing FFT spectrum. The simulation results show that the new focus measure can effectively express the defocused states for the real remote sensing images. The error ratio is only 0.112, while the prevalent algorithm based on the FFT spectrum is as high as 0.4. Compared with the FFT-based method, the proposed algorithm performs at a high reliability in the real imaging experiments, where it reduces the instability from 0.600 to 0.161. Two experimental results demonstrate that the proposed algorithm has the characteristics of good monotonicity, high sensitivity, and accuracy. The new algorithm can satisfy the autofocusing requirements for TDI CCD space cameras.

© 2012 Optical Society of America

OCIS Codes
(070.4790) Fourier optics and signal processing : Spectrum analysis
(100.0100) Image processing : Image processing
(100.2960) Image processing : Image analysis
(100.7410) Image processing : Wavelets
(280.0280) Remote sensing and sensors : Remote sensing and sensors

ToC Category:
Image Processing

Original Manuscript: April 13, 2012
Revised Manuscript: June 13, 2012
Manuscript Accepted: June 13, 2012
Published: July 18, 2012

Shuping Tao, Guang Jin, Xuyan Zhang, Hongsong Qu, and Yuan An, "Wavelet power spectrum-based autofocusing algorithm for time delayed and integration charge coupled device space camera," Appl. Opt. 51, 5216-5223 (2012)

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