This paper proposes a novel projection-based filter, which is applied in the digital image processing. This filter is easy to implement by combining linearly the original image with its horizontal and vertical projections. The principle and property of the proposed filter are discussed in detail, and abundant experiments have been done in digital image filtering. It is proved that the filter can reduce the data and enhance the main feature without losing the information about the original data. We paid more attention to the application of feature enhancement in our experiment.