Hitachi CML174 17'' LCD Plus Samsung 172T Revisted

Contrast Ratios and You

Unfortunately, screen uniformity was not the only category that Samsung took the crown.  The CML174 has a slightly higher brightness rating, but lacks a high contrast ratio.  There are several immediate effects for this, which explain the problems with vivid color reproduction on the CML174.

Basically, to calculate the contrast ratio, the values of the darkest black and the lightest white are first obtained.  The ratio of the light over the dark value produces a fraction which is then reduced to a whole number.  Even though the measurement may be simple, the specification itself is not.  VESA publishes at least six different methods of obtaining contrast ratio measurements.  To further complicate matters, some manufacturers decide to take off angle measurements (to reduce glare) or darkroom measurements.  For example, some monitors might state they have a 500:1 contrast ratio at 5 degrees. 

Even though contrast ratio and brightness are not dependant on each other, they do work measure similar qualities.  We can imagine the brightness (luminance) as the upper bound on a contrast ratio, and crudely illustrate the color depth of an image inside that contrast ratio.  If a color is allowed more depth in light and dark values, it produces more vibrant tones.  Essentially, this generates less strain on the eyes (try reading white text on grey paper).  For a gaming LCD, we definitely would have enjoyed a higher contrast ratio on the CML174. 

Some people reading this may ask why there are no contrast ratios for CDT/CRT’s.  Simply put, LCD’s need a light source shining behind the pixels at all times, even to produce just a single white pixel.  A traditional CRT differs by dimming the electron gun behind a certain pixel to produce black.  True black on a CRT produces a luminance of near zero.  By dividing the lightest light by the darkest dark luminance values (cd/m^2) on a CRT, one might conclude the contrast ratio would equal infinity.  Sales teams attempting to explain a specification of infinity do not typically agree with the marketing representatives in most companies.  (If you are number two in the sector you may have to start marketing the contrast ratio as infinity+).  Thus, for CRT’s the measurement becomes irrelevant.

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The higher contrast ratios provide a quick reference for how vivid colors might appear on the screen, but we have to keep in mind that it requires brightness measurements as well.  The VESA FPDM2 handbook jokingly portrays a cartoon stating something along the lines of “Well it says 102:1 contrast ratio but it certainly looks better than that!”  Unfortunately, contrast ratios are a flawed and unreliable measurement, but the LCD sector depends on it too much for it to be removed from screen specifications.