For determining the optimum parameters of the transformation function in nonlinear image enhancement processingintelligent optimization algorithm is usually used for automatic optimizationin which the fitness function has great influence on the optimizing performance and image enhancement effect.Generallyonly image energy is included in fitness function for image quality assessment.In factthere are several other important factors as information entropyfirmnessthe change between signal and noiseand pixel difference and so on.Taking full account of the 5 factors above and considering both the global and local imageboth the whole structure and small detailswe designed a new fitness function.The new fitness function was used in genetic algorithm and particle swarm optimization to enhance the imageand the experiment results showed that the algorithm has fine selfadaptabilityand the enhancing quality is improved significantly.