Li-qiang GUO, Lian LIU. Image focus measure based on slant transform and variance. [J]. Optics and Precision Engineering 29(7):1731-1739(2021)
DOI:
Li-qiang GUO, Lian LIU. Image focus measure based on slant transform and variance. [J]. Optics and Precision Engineering 29(7):1731-1739(2021) DOI: 10.37188/OPE.2020.0555.
Image focus measure based on slant transform and variance
Focus measure is easy to be interfered by the noise in the autofocusing process for a camera and electronic microscope. In order to solve this problem, we combine the slant transform in image processing with the variance in statistics to propose a novel focusing measure with noise robustness. First, the image is divided into small blocks to facilitate the subsequent acquisition of the sharpness index of each local sub image. Then, we perform the slant transform on each sub image to obtain the frequency coefficients. In the transform domain, we calculate the absolute value of the mid-frequency coefficient, and perform the summation operation to obtain the sharpness index of each sub image. Finally, the variance of each sub image sharpness index is calculated, and the result is taken as the final focus measure of the whole image. By extracting the mid-frequency information of local sub images and solving the global variance, the proposed focus measure has strong noise robustness. The experiments on LIVE image database indicate that compared with the typical focus measure, the noise robustness of the proposed method is better than the existing classical algorithms, where the sharpness detection ability (SDA) and the discreteness evaluation indexes are improved by 20.27% and 125.61% averagely.
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