Adaptive local contrast enhancement method for medical images displayed on a video monitor.

It is known that light-box luminance is an important factor in the detection of objects on radiographs. Existing methods for image contrast enhancement do not consider the luminance effect so that the enhancement may be inappropriate for the processed image displayed on a video monitor. Based on the properties of human visual system (HVS), an adaptive local contrast enhancement (ALCE) method was developed to enhance the medical image displayed on the video monitor by investigating the influence on human eyes of display luminance difference between a conventional light-box and a video monitor. The HVS model indicated parts of a radiograph unclear to human eyes at a given display luminance. By calculating the contrast of the image pixel by pixel, we found the parts of an image that are needed to be amplified at low display luminance and provided these parts with adequate enhancement. The processed image displayed on a video monitor was visually equivalent to the raw radiograph displayed on a light-box. A quantitative evaluation method of image quality assessment was used to compare the ALCE-processed image with others.