Display Standard - Veritas et Visus

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Veritas et Visus Display Standard February 2009 Panasonic -- PDP Sharp – LCD Girl with Painted Face – notice the change in the skin color in the off-axis LCD Photographer Steve Kelly Panasonic – PDP Samsung – LCD Spanish Oranges – notice the oranges change color and look like pinkish grapefruits in the off-axis LCD Photographer Sergio Parisi Panasonic - PDP LG – LCD New York City at Night – the LG LCD produces a noticeably hazy background, especially in off-angle viewing Photographer Paulo Barcellos Jr. 68
Veritas et Visus Display Standard February 2009 Photometry and colorimetry measurements: This section presents photometry and colorimetry measurements for the LCD models from LG, Samsung, Sharp and Sony. Three of the units are the current top-of-the-line flagship models. All of the units were set up for optimum image and picture quality using only standard user menus and user controls. The selections and settings were all chosen to have each unit perform as closely as possible to a high quality HDTV studio monitor. In particular, all settings that dynamically process the image were disabled, such as dynamic contrast, dynamic backlight, dynamic black, dynamic white, and dynamic color. Many of these functions are given proprietary names by each manufacturer. The units were all fed digital HDMI signals. DisplayMate test patterns were used to accurately set the black level to 16, the peak white clipping level to 255, and the white point chromaticity as close to D65 as possible. The measurements were made after a minimum one-hour warm up period with a Konica Minolta CS-200 Spectroradiometer set for a 1-degree acceptance angle. Luminance and contrast ratio: Table 3 summarizes the principal photometry measurements. The “Highest Calibrated Luminance” is the maximum luminance that the unit can produce while calibrated as described above. For most LCDs, this was obtained from the highest backlight setting available. For side-by-side comparisons the backlight for each of the LCD units was adjusted to provide comparable luminance, about 200 cd/m 2 for the largescreen flagship units, and somewhat higher at about 250 cd/m 2 for the mid-line units. Highest Calibrated Luminance Peak Luminance Setting Used 69 Contrast Ratio Correlated Color Temperature Gamma Samsung LCD 427 cd/m 2 189 cd/m 2 1,877 7035 K 2.25 Sharp LCD 307 cd/m 2 192 cd/m 2 1,330 7334 K 2.23 - varies Sony LCD 362 cd/m 2 202 cd/m 2 1,344 6495 K 2.17 LG LCD 384 cd/m 2 251 cd/m 2 511 6463 K 2.13 - varies Table 3: Photometry and colorimetry measurements summary Source: DisplayMate Technologies and Insight Media Transfer function and gamma: Figures 3 to 7 plot the transfer functions for various combinations of the HDTVs. The plots extend down to 10% of peak signal intensity, which corresponds to 0.0063 of the peak luminance for the standard gamma of 2.20. Gamma is a parameter that specifies how the luminance changes with signal input level. Originally based on the performance of the CRT, the luminance “L” is presumed to vary with signal “S” as a pure mathematical power-law in the form L2/L1 = (S2/S1) Gamma . In particular, when plotted on a log-log graph the slope of any portion of the transfer function is its local gamma. If the transfer function is a perfectly straight line on a log-log graph, then gamma is a constant. If it isn’t a straight line then gamma varies with signal level. The logarithmic slope of the transfer function is the gamma for the display, which is listed for each unit in Table 3. When the transfer function is not a perfectly straight line on a log-log graph, then the gamma varies over the signal intensity range. The gamma values listed in Table 3 were measured over the signal intensity range from 90 to 40% of maximum. The ideal standard gamma value for HDTVs is 2.20. Note that if the transfer function is not a perfectly straight line, then the effective gamma changes with anything that affects the operating points for the signal intensity range, such as the setting of the contrast/picture control or any other function that affects video gain or signal levels.
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