Auto Contrast evaluates the combined grayscale intensity of all three color channels in an image. It adjusts by setting the darkest pixels to pure black and the lightest pixels to pure white, while redistributing the remaining tonal values in between. This process enhances the overall contrast of the image without altering its colors. It simply boosts the overall contrast, making it a good choice for images that don't suffer from any sort of color problems and just need a bit more "pop".