A system and process for improving the uniformity of the exposure and tone of a digital image

摘要

A system and method for manipulating a set of images of a static scene captured at different exposures (i.e., "bracketed" images) to yield a composite image with improved uniformity in exposure and tone. In general, the aforementioned goal can be achieved by analyzing a set of bracketed images using a multi-dimensional histogram and merging the images via an approach that projects pixels onto a curve that fits the data. However, it has been found that the desired composite image can be produced in a simpler manner by summing the pixel brightness levels across the multiple images, followed by an equalization process. One possible equalization process involves simply averaging the summed pixel brightness values by dividing the summed value of each pixel set (i.e., groups of corresponding pixels from the bracketed images) by the number of bracketed images. An even better result can be achieved using a histogram equalization process. In essence, this histogram equalization involves creating a count of the number of pixels sets having the same summed brightness level. From this count, a cumulative distribution function is computed and normalized to a maximum value corresponding to the maximum summed brightness level. The cumulative distribution function is then used to determine new pixel brightness levels for use in generating the composite image.