A wavelet auto-focusing method is proposed to consider the characteristic of the aerial camera CCD mosaicing structure. In order to evaluate the clarity of the image obtained by the aerial camera, an image assessing function is constructed based on the wavelet transform. The evaluation function is constructed by the wavelet coefficients of the image, and the characteristic of the CCD mosaicing structure was taken use to solve the problem that the evaluating values can't be compared for the variable images. On the basis of the wavelet evaluating function, the quality of the image was assessed. Then the CCD mosaicing structure was utilized to perform auto-focusing process, and a simulation was made to validate the novel method in the end. The weights are set according to the characteristic of the human vision system (HVS). In order to make the function adaptive to different images, the properties of the wavelet basis are analyzed. At the same time, the area with high frequency component is chosen as the evaluating area so as to improve the sensitivity of the evaluating function. And the flow chart of the focusing based on this method is described particularly. There are some innovation in this paper, such as: the weights of the wavelet coefficients in the evaluating function were set according to the characteristic of the wavelet transform and HVS, which is close to human subjective feel and insensitive to noise|the properties of the wavelet basis were analyzed so as to make the function adaptive to images with different high-frequency components|the wavelet basis with the best effect is symlet2 and the level of decomposing is three|the problem that auto-focusing of the aerial camera can't use digital images processing directly was solved by making use of the CCD mosaicing structure. All in all, this paper introduces a wavelet auto-focusing method based on digital image processing to aerial camera used the characteristic of CCD mosaicing structure. The function is close to the HVS subjective feeling and adaptive to objects with different frequency components, and this method is more sensitive and adaptive than traditional wavelet methods. It could obtain high image quality, and is suitable to the application in focusing system of the aerial camera.
LI Shanshan, GONG Huili, LIU Yang, HU Zhuowei
. A Wavelet Auto-focusing Method of the Aerial Camera Based on CCD Mosaicing[J]. Journal of Geo-information Science, 2012
, 14(1)
: 101
-108,122
.
DOI: 10.3724/SP.J.1047.2012.00101
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