A Bayes-spectral-entropy-based measure of camera focus using a discrete cosine transform

Authors:
Matej Kristan;Janez Perš;Matej Perše;Stanislav Kovačič
Affiliations:
Faculty of Electrical Engineering, University of Ljubljana, Traška 25, 1001 Ljubljana, Slovenia;Faculty of Electrical Engineering, University of Ljubljana, Traška 25, 1001 Ljubljana, Slovenia;Faculty of Electrical Engineering, University of Ljubljana, Traška 25, 1001 Ljubljana, Slovenia;Faculty of Electrical Engineering, University of Ljubljana, Traška 25, 1001 Ljubljana, Slovenia
Venue:
Pattern Recognition Letters
Year:
2006

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Abstract

In this paper we present a novel measure of camera focus based on the Bayes spectral entropy of an image spectrum. In order to estimate the degree of focus, the image is divided into non-overlapping sub-images of 8x8 pixels. Next, sharpness values are calculated separately for each sub-image and their mean is taken as a measure of the overall focus. The sub-image spectra are obtained by an 8x8 discrete cosine transform (DCT). Comparisons were made against four well-known measures that were chosen as reference, on images captured with a standard visible-light camera and a thermal camera. The proposed measure outperformed the reference measures by exhibiting a wider working range and a smaller failure rate. To assess its robustness to noise, additional tests were conducted with noisy images.