A key question of multi-focus image fusion is how to decide the clarity of the source images. To solve this problem

a new focus measure is proposed. The new focus measure based on properties of local extrema is proposed

namely

the normalized structure extrema. We propose a fast image fusion method based on the new focus measure and a quick estimation of the fusion decision matrix. With the new criterion of image clarity and the fusion method introduced in the paper

multi-focus image fusion yield superior performance than the conventional approaches in terms of the test results. Normalized structure extrema number is a new focus measure that can judge the clarity of a region effectively and more robustly against pulse noise. Compared with some traditional methods of multi-focus image fusion on both the subjective visual effect and objective evaluation

it indicates that the presented method improves the fused results and efficiency saliently.