A histogram is a graphical display representing the tones distribution within an image. The horizontal coordinate represents each Pixels are the smallest unit of a digital display or digital image. A raster or bitmap image is made... More value possible from Black is the fourth color in the process of four-color printing. The "K" in CMYK. Black adds tonal d... More to white. The vertical values indicate the number of pixels in the image that occur at each value level.