In this paper, we propose an efficient algorithm for the measure of contrast in digital images. It applies locally, at various sub-sampled levels, a simplified computation of local contrast and finally it recombines all the values to obtain a global measure; in this way, this measure has a computational complexity lower than alternative local methods, keeping a comparable level of correctness in the contrast estimate. In order to test the soundness of our method, we have carried out two kinds of test: objective and subjective. Then the results have been compared with those of the algorithms proposed by other researchers. Tests and results are presented and discussed in detail.