DIGITAL IMAGE PROCESSING METHOD FOR OVER AND UNDER EXPOSED PHOTOGRAPHIC IMAGES

In a method of digital image processing employing a tone reproduction function generated by normalizing the histogram of a sample of tone values selected from the image, it is an object to automatically detect images that were derived from over or under exposed photographic originals and to adjust the tone scale of such images to improve their appearance. The invention achieves this objective by testing the skewness of the sample of tone values of the image and if the amount of skewness exceeds a predetermined amount, adjusting the contrast of the processed image by an amount equal to the value of a standard variate computed for the sample at a mean tone value of the sample minus the value of a standard variate computed for the sample at a mode of the tone values of the sample.