The present invention is directed to a digital image content-adaptive contrast improving method. The method includes forming a piecewise linear tone remapping function for a digital image according to the histogram thereof. The piecewise linear tone remapping function is formed by repeatedly performing a first and a second step. The first step determines a starting linear tone mapping function for a specific range of luminance values. The second step generates a new tone mapping function for the specific range of luminance values based on the starting linear tone mapping function and the histogram. An apparatus for implementing the method is also provided.