Black Level
The black level of the picture, adjusted with the user Brightness control, determines how much light is produced in the darkest portions of the picture. If there isn't enough light, dark gray "shadow" detail is lost, with those areas of the picture being seen as all black. If there is too much light in dark portions of the picture, what should be black is seen as some shade of gray. This causes the picture to have a milky, washed-out look with low contrast.
The proper adjustment of black level depends on the amount of ambient light in the room. The Brightness control will usually need to be adjusted to one position at night and another position during the day, depending on the level of ambient light in your viewing environment. The factory usually presets the default black level very high, to compensate for high ambient light levels on most dealer showroom floors. If the display has multiple viewing modes (e.g. Theater, Movie, Sports), the default black level can be preset in each viewing mode to compensate for each different level of ambient light in your viewing environment. This calibration is made using a special PLUGE (Picture Line Up Generating Equipment) test pattern, with tests performed with both bright and dark test patterns.
White level
The white level of the picture, adjusted with the user Contrast control, determines how much light is produced in brightest portions of the picture. If the control is adjusted too low (rarely the case), the white portions of the picture appear dark and dinghy. If the Contrast control is adjusted too high on a CRT (cathode ray tube)-based display, bright portions of the picture will often "bloom," being pushed out of focus. Also, portions of the picture may show geometric distortion, with line bending and bowing taking place as scene brightness levels change. This excessive contrast setting places an extreme strain on the CRT(s), decreasing the CRT life drastically. If the Contrast control is adjusted too high on a non-CRT display, all the brighter levels of a scene may blend together at the same brightness level, resulting in the loss of high brightness picture detail.
The factory usually presets the default white level extremely high, resulting in a very bright, distorted picture, and shortened CRT life if left in that condition. Everybody wants their display to show as bright a picture as possible, yet you don't want to unneccesarily shorten your expensive CRT life, distort the picture, or lose bright picture detail. This leads to just one optimum setting of the Contrast control; as bright as possible without losing picture accuracy. Once the default setting of the control is calibrated to this optimum setting, there should be no reason to ever readjust the control. This calibration is made using both a needle pulse test pattern with gray scale range and a high white level fine step test pattern to detect white compression.
Chroma Saturation
The chroma saturation of colored portions of the picture, adjusted with the user Color control, determines the intensity of reproduced colors. If the Color control is adjusted too low, vivid colors in the picture are reproduced as too pastel, or washed out, and pastel colors are reproduced with almost no visible color. If the Color control is adjusted too high, vivid colors will be glaring, with most faces appearing almost sunburned.
The proper adjustment of the Color control is complicated, however, because most manufacturers adjust the color decoder to over-accentuate red colors (red decoder push). This is done to somewhat compensate for the whites which are adjusted to be "too blue," to produce the perception of higher brightness. If the color decoder isn't readjusted for accurate operation, faces will have a glaring, sunburned look, even with accurate calibration of the Color control. Note that if the Color control is simply adjusted to make red portions of the scene look right, all other colors will be weak and washed out.
The Color control is not active when an RGB video signal is input to a display, as the characteristics of the RGB input signal totally control the reproduced color intensity. The RGB input signal path inside the display also bypasses the color decoder, and eliminates that as a source of color inaccuracies.
Chroma saturation is calibrated with a color bar test pattern developed by SMPTE (Society of Motion Picture and Television Engineers), along with red, green, and blue optical filters. If red decoder push is detected, the color decoder is readjusted for accurate color decoding (if possible), and the chroma saturation is re-calibrated. If the color decoder isn't adjustable, a compromise saturation level is selected to minimize excessive red without washing out greens and blues. If an Auto Color""feature" is present, it is also defeated to obtain the most accurate color control.
Chroma Hue
The chroma hue, adjusted with the user Hue or Tint control, determines the color of the colors. If the Hue control is mis-adjusted, red colors are reproduced as either more green or more magenta. All other reproduced colors are shifted in a similar fashion. The hue control is usually adjusted by a consumer to make flesh tones look right. If other colors still don't look right, there isn’t much the consumer can do about it.
The reason for not all colors looking right at the same adjustment of the Hue control is, again, a color decoder with "red push" (assuming proper white balance calibration). If the color decoder isn't accurate, green objects will be too blue and yellow objects will be too orange, even with proper flesh tone adjustment, and all other colors will be at least slightly wrong. Chroma hue is calibrated with the same SMPTE color bar test pattern and optical filters.
Sharpness
The Sharpness user control adjusts how much "enhancement" is added to picture edges to make them appear "sharper." This feature is often marketed as allowing the viewer to adjust how much picture detail they wish to see (which was beneficial before TVs used comb filters). The problem is that adjusting this control for sharper picture detail adds extra lines (junk) to the picture, just to the left or the right of each picture edge. This tends to muddy up the picture with information that shouldn't be there (artifacts). Misadjustment of this control is one of the major contributors to the loss of film-like picture quality. For the most accurate, film-like picture, this control should be calibrated for maximum possible picture detail without added picture artifacts, and then should never be adjusted again. This calibration is accomplished with picture resolution and line detail test patterns.
Scan Velocity Modulation (SVM)
While Scan Velocity Modulation is neither a user control nor a service control, it is another "feature" which is marketed as increasing the picture detail. SVM works by varying the speed of the electron beam as it travels from the left to the right side of the screen, dependent upon the brightness in each area of the picture. Within bright areas of the picture, the electron beam speeds up, and within dark areas, it slows down. This can be seen quite easily on a needle pulse pattern as the black lines being wider than the white lines. The desired effect is to make small, dark picture detail more visible. The actual effect is usually smeared picture detail, resulting in a muddied, lifeless looking picture - definitely not film-like. The feature isn't adjustable, but in some cases can be switched off on a service menu, defeated by using a particular picture mode (e.g. Film Mode), or can be disconnected inside the display.
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