What The Experts Say
Following on from my earlier discussion of "Settings by Eye" here's what the experts at the
Image Science Foundation has to say on the subject of settings and calibration.
I recognize there's quite a bit to read but its worth it because not only does it provide guidance for getting the best out of our set, there are clues about what the service menu settings do.
Grey-scale
To calibrate a display to any color of white requires, at minimum, the ability to adjust two of the three primary colors (red, green and blue) that combine to create grayscale. Depending on the display, there may be three color controls for the dark end of the grayscale range (typically referred to as “cutoffs” or “bias”) and three for the white end (“drives” or “gains”), but controls for at least two colors is required for color temperature adjustment. It is necessary to have these same controls for both the black end of the grayscale range (“black level” or “brightness”) and the white end of the range (“contrast,” or “picture”). These “cutoff” and “drive” controls are adjusted until the best possible color temperature tracking is achieved across the entire range, from video black to peak white. The labels used for grayscale adjustment controls vary widely among manufacturers.
Gamma
Gamma refers to the change in light output as the video signal increases from one reference level to the next, as measured in IRE units. The gamma response is typically checked at each 10 IRE step from 0 to 100 IRE, but it is also possible to measure and report gamma response at 1 or 5 IRE steps. According to the prevailing Society of Motion Picture and Television Engineers (SMPTE) standard, the correct gamma response is 2.2 at each step. In real world applications, a display gamma ranging from 2.2 to 2.5 is desired, and this will vary according to the display technology and viewing environment.
A gamma that is too low overall will contribute to images appearing dull and lifeless, while gamma that is too high will produce images that appear to be overly dynamic and visually fatiguing. While picture gamma is generally considered as an overall measure across the grayscale range, extreme gamma errors occurring in isolated areas of the gamma curve can also adversely impact overall image quality.
Setting contrast and brightness correctly is a key component in achieving proper gamma response, as these components have a strong influence on the composition of the extreme ends of the gamma curve, while the supporting gamma controls allow adjustment of specific areas between the dark and bright ends of the range.
Colour
Color decoding consists of accurately recovering the red, green and blue color channels from a non-RGB format such as S-Video, composite video or component video, and processing them for correct color response. All color decoders are built upon a foundation of the color and tint controls, which simultaneously alter the response of all three color channels. A color decoder is typically initially adjusted for the blue color channel, using the color and tint controls that are found in either the user or service menus. Proper alignment of the red and green channels is also required, and to achieve this individual and independent saturation and phase controls are required for red and green. Full color decoding controls are required not only to properly calibrate the display but also to compensate for source errors.
Colour Management
Color Management refers to a series of controls to align the red, green and blue primaries and the cyan, magenta and yellow secondaries. With the proper test equipment and patterns it is possible to fully correct a display that was designed by the manufacturer for non-standard primary and secondary colors. Most consumers are surprised to find that there are standards for both the primary and secondary colors that are used in televisions to create color images. Even more surprising is the fact that it is very difficult to buy a television that adheres to these standards. Display manufacturers choose to ignore these standards because they believe that using a customized color gamut will provide their products with a unique look and another helpful element of differentiation in a highly competitive market.
Color decoding is not to be confused with color management and refers to the color signal encoded in composite video, s-video and component video connections that will be decoded into the original red, green and blue signals for the final process of displaying the image. For digital displays this final process requires Color Management circuitry to steer the primary colors the design uses to the color decoded signals provided to match SMPTE-C or HDTV color gamuts. Both must be correct for accurate color reproduction.
There are many different approaches to color management but not all of them work as advertised. In addition, making use of these color management controls requires the use of properly designed and calibrated test equipment. Blindly adjusting these controls creates a risk of more serious imaging issues than the incorrect primary and secondary colors provided by the manufacturer.
Sharpness
Features that claim to “enhance” or “correct” some aspect of video display performance typically involve a significant degree of manipulation or distortion of the source video signal. By definition, such extracurricular video processing violates the most fundamental goal of proper display design – faithfully delivering the complete and unaltered content of the source video signal, in compliance with agreed industry standards. While a casual viewer or uneducated consumer may find some initial appeal in edge enhancement, for the discriminating viewer, edge enhancement seriously distorts picture quality. As a result, there must be some means for selectively reducing or defeating edge enhancement, so that the display is capable of accurately reproducing the content of the source video signal.
Note that the range and presence of edge enhancement varies widely among manufacturers, technologies and form factors.
Edge enhancement does precisely what it says it does; therefore, defeating edge enhancement will result in a comparatively “softer” image. While it may appear that the “edge enhanced” picture is superior, that isn’t the case – it simply takes time to acclimate to and appreciate the unprocessed picture without the artifacts induced by such circuitry.