A weighted averaging algorithm of image zooming-out based on image sub-block information is presented in this paper. This algorithm overcomes the shortcoming of some common algorithms of image zooming-out that will lead to image visible distortion. First

according to the scale-down proportion the sub-block of every pixel at zoomed-out image is obtained from original image

and then the value of every pixel can be calculated based on corresponding sub-block by the method of weighted averaging. In the process of zooming-out the whole image information is reserved to the greatest degree

and the image after zoomed-out shows good integrity. The algorithm is simple

effective and rapid. The experimental results show that the advantage is evident compared with the common algorithms especially at image integrity. But the contrast of the image is reduced. To solve this problem the paper advances an extension of gray-scale method to improve the quality of zoomed-out image in the end of the paper. The experiments have verified the effectivity of the algorithm in this paper.