Settings for contrast (white levels) and brightness (black levels) are critical to the proper viewing of a picture on a video monitor or television.
The blacker the blacks and the whiter the whites the better the contrast ratio. If misadjusted, the picture looks too washed out or bright objects smear or bloom. The best balance is achieved by careful analysis of your monitor’s performance by providing controlled signals representing the “whitest white” and “blackest black”. Always keep in mind that the room environment will affect these settings. Making adjustments in a sunny room will result in a brighter setting than if adjustments are made in the evening. So it’s wise to make adjustments under the viewing conditions likely to exist when you watch the movie. Motion pictures are mastered in a room that’s moderately dark. White levels (contrast) are adjusted to 35-foot lamberts using a light meter and a signal very much like what’s provided by THX Optimizer. We don’t expect you to use a light meter, but the THX Optimizer test has been designed to deliver results very close to what’s achieved during mastering.
Video is measured on expensive test equipment during the post production process. The scale on a waveform monitor is graduated in IRE units (Institute of Radio Engineers, the group that set this measurement standard). For DVD component video, the useful picture content of the video signal is measured as a percentage, where 0% represents black and 100% is white. With VHS, Broadcast and the composite video output of your DVD player, the black level for NTSC is elevated to 7.5% IRE. Normally, the picture intensity is clipped, or not allowed to exceed 100% IRE and little if any information transitions above this level.
The Contrast/Picture adjustment procedure provides a box with four distinct shades of white in eight boxes surrounded by black.
If the Contrast/Picture control is set too high, you can lose the distinction between the various white boxes and can result in picture bleeding, which is the oversaturation of the picture tube. This can be seen as a solarization or blooming of the picture highlights (see Figure 1). This can also be noticed on the right side of the white block as it transitions to black due to the way the picture tube is scanned. The brightest white boxes will represent the highest video level in the feature. The goal here is to adjust your Contrast/Picture control on your television/monitor to a point where the large white area is bright but all four shades of white are still visible. At the same time, insure that the transitions from black to white and white to black have no smearing.
As your picture tube ages, this will be one of the more difficult adjustments to make. The light level produced by the picture tube decreases with age, making it necessary to drive the picture tube harder. The harder the picture tube is driven, the less likely the beam scanning the front of the screen remains sharply focused. If you notice any of the mentioned defects, it doesn’t mean you need a new monitor or television. It may only require a visit from your local television service agency to make some adjustments.