Intensity-pair distribution was recently proposed to enhance the contrast of an image. There are several parameters provided in that algorithm for users to control the enhancement. With a proper combination of parameters, the algorithm provides satisfying contrast enhancement without noise amplification, unnatural look, and other common drawbacks that are seen in previous work, but there is no effective method of parameter selection mentioned. In this paper, we proposed an effective criterion based on human visual system to decide a proper combination of parameters. With an appropriate combination of parameters, we can take the most advantage of that algorithm. Automation of parameter selection can easily be done by iteratively using the proposed algorithm. We presented experimental results to compare results of contrast enhancement with proper and improper combinations of parameters.