detail in transitions in the horizontal direction, is partially determined by Contrast level. It goes down as contrast goes up. In the video world, horizontal resolution is measured in terms of a distance along the horizontal axis equal to the height of the picture. If we say that a picture has 425 lines of horizontal lines per picture height, 425 lines would be exhibited to about 3/4 of the way across the picture. Horizontal resolution is measured in terms of picture height because the width of the line is 1.33 time the height. Larger numbers in the horizontal direction would be more difficult to interpret in terms of overall picture resolution if they were not expressed in terms of the height. The computer world chooses to specify horizontal resolution across the entire width of the line. A 640 by 480 picture has an equal picture resolution capability in both the horizontal and vertical direction. Who would ever guess that by looking at the numbers? If that were specified the way it is done in the television world, the horizontal resolution would be 480 lines per picture height and the vertical resolution would be 480 lines.