Articles: Monitors

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This is most obvious from the so-called CIE color diagram. The CIE color space describes a particular color tone with three coordinates: two determine the color and the third determines the brightness. The diagram has only two (color) coordinates and outlines the color space perceived by the human eye (the borderline of this space corresponds to pure colors, from a monochromic light source, while the internal area is represented with colors of a more complex spectrum):

The white triangle on this diagram bounds the area that corresponds to the color range of sRGB-compliant devices and the white dot in the middle of the triangle is the white color point at a color temperature of 6500K. As you see, the range of sRGB colors is small compared to the range the human eye can perceive, so many colors are left off when the image is created (for example, an sRGB monitor cannot reproduce a single pure color at all) – they are just replaced with the colors that lie on the edges of the triangle. Sometimes this leads to noticeable visual artifacts, of course.

Besides sRGB, there are other color spaces that describe much wider color ranges. First of all, I mean AdobeRGB and NTSC as they are more often referred to in monitor-related discussions. While the sRGB color space embraces only 35% of the colors perceived by the human eye, AdobeRGB covers 50.6% of them, and NTSC – 54.2%. Well, almost all monitors today comply with the sRGB standard, and since the gamut range is determined physically by the characteristics of the backlight lamps and the color filters of LCD monitors and phosphors of the CRT monitors, there is a small variation between different models (even, between CRT and LCD ones) when it comes to color reproduction. Other factors influence it much more.

Exceptions to this rule are some professional-class CRT monitors. Not long ago, NEC-Mitsubishi introduced a 22” RDF225WG model with a gamut range of 97.6% of the AdobeRGB space thanks to a better green phosphor (as the above-shown diagram suggests, the green color is the most problematic). In the next year LCD monitors are expected with a gamut range wider than that of the AdobeRGB standard, although by 1% only. Unlike in the CRT model from NEC-Mitsubishi, the LCD models will achieve it by using white LED highlighting instead of traditional mercury-based cold-cathode lamps. The lamps have an irregular spectrum, consisting of several peaks and stripes, while light-emitting diodes produce a more even light, which also fits well into the passbands of the matrix’s light filters, improving the image.

Right now such monitors are under development. Of course, they will be oriented on professional applications, with appropriate prices. LED highlighting will come to home monitors eventually, if LCD matrices haven’t given way to OLED matrices (which don’t require backlighting at all) by that time. Well, I wouldn’t pay much attention to that. The fact that the first CRT monitor with a gamut range close to AdobeRGB was only released in the last spring, while the color correction industry is a few decades old, indicates that gamut range is not the determining color reproduction factor.

As you see, a good reproduction of color is a hard and complex task. When talking about contrast, viewing angles or response time, I could say that the value declared by the manufacturers described but some of the characteristics, but here the text “16.7 millions of colors” means nothing at all with respect to color reproduction.

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