Articles: Monitors

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The brightness and contrast measurements give out expectable results that comply with the monitors’ specifications. The model on the S-PVA matrix has a higher maximum brightness as well as a higher contrast ratio.

I began this section of the review with a description of NEC’s line-up of professional 21” monitors, including SpectraView series. What puts it apart from the two tested models?

The SpectraView 2190 model is identical to the LCD2190UXi on the hardware level (but the LCD2190UXp doesn’t have a SpectraView counterpart). The only difference is the hardware calibration software.

Each LCD monitor has a so-called Lookup Table (LUT) which stores correspondences between the input signal and the signal that must be sent to the matrix to achieve the necessary color. The matrix’s own characteristic is S-shaped and it must be converted into an exponential gamma curve. It is the precision of values in the LUT and the accuracy of calculations performed over them (the monitor must not only convert one signal into another, but to take into account such settings as contrast, color temperature, etc) that determines the quality of color reproduction, i.e. the accurate shape of gamma curves, the difference of color temperatures between different levels of gray, the lack of banding in smooth color gradients, etc.

In a majority of monitors the LUT is written into memory at the factory and cannot be changed by the user. You can’t do anything about the monitor when its parameters begin to degenerate with time or if it turns out that the factory LUT doesn’t provide the necessary precision at the settings you want to use.

To correct the image in this case, you should use a hardware calibrator or spectrophotometer. This device has photo-sensors that are installed on the screen and different colors are then sequentially displayed under the sensors. The sensor measures what exactly color the monitor displays and, knowing which color it should be, determines the correction coefficient. But the monitor’s LUT being inaccessible, this coefficient is either written into the graphics card’s LUT or into an ICC file which can be used by software (programs like Adobe Photoshop) to correct the image they show on the display in accordance with the monitor’s parameters.

This approach has two drawbacks. First, both of them are software-dependent. Second, any additional transformation brings in its own distortions, even though small ones. To avoid this problem (which is, however, only important for applications that require an ideal reproduction of color), monitors with a programmable LUT are produced. It is not difficult to implement such a LUT.

The LCD2190UXi and LCD2190UXp are such monitors, formally. They have a rewritable LUT that can be accessed from the PC by means of the GammaComp program. But this is only formally. To write data into the LUT, you should first connect a calibrator to the PC and obtain those data. But calibrators create standard ICC profiles whereas GammaComp wants to have an ordinary table in CSV format that contains values that must be written into the monitor’s LUT. No table – no LUT. And calibrators cannot create such tables. Thus, these monitors have hardware calibration, but you can’t use it.

Although the SpectraView 2190 is a copy of the LCD2190UXi on the hardware level, it features an important accessory, a GretagMacbeth calibrator with special software that can receive data about the monitor from the calibrator and write them directly into the monitor’s LUT. Thus, having selected necessary settings on the monitor, you can start the calibration process and get as accurate a color reproduction in a quarter of an hour as is possible at all on this model. And the necessary parameters are all written into the monitor itself.

I don’t think that many people need such a high accuracy, though. A majority of users are going to be satisfied with the factory setup of the 2190 series, which is almost ideal, as you have seen above.

But besides the SpectraView 2190 there is a more expensive model of the same series, SpectraView Reference 21 (LCD2180WG-LED). It is based on an S-IPS matrix with LED backlight which provides an enhanced color gamut (if you don’t know what the term color gamut means and why it is enhanced, refer to the previous article).

As the model number suggests, the Reference 21 is based on the previous platform, the 2180 series. It means it lacks some minor features the newer 2190 series has, like the automatic adjustment of brightness depending on the ambient lighting, or the option of disabling the Power indicator LED, etc. When it comes to image quality, the only drawback is that it uses 10-bit precision for internal calculations (and, accordingly, a 10-bit LUT) as opposed to 12-bit precision in the 2190 series monitors. Of course, the Reference 21 supports hardware calibration in full, although the calibrator has to be purchased separately (the calibrators included with the 2190 series are not recommended – NEC says there is a special model for the Reference 21 that is set up and tested for use especially with enhanced-color-gamut monitors).

An interesting feature of the Reference 21, which is missing in the 2190 series, is its 10-bit digital input. If you’ve got an appropriate graphics card (e.g. AMD/ATI’s X1000 series GPUs can give out 10-bit color via DVI), you’ll get a fully 30-bit graphics subsystem (three 10-bit colors) as opposed to the ordinary 24-bit one (three 8-bit colors). This is a useful innovation because the human eye can indeed perceive gradations of 8-bit color on a good monitor. So if the highest-accuracy color reproduction is the goal, the transition from 8 to 10 bits (or from 24 to 30 bits, if you count up all the three basic colors) won’t be excessive.

The main feature of the Reference 21 is its LED-based backlighting which endows it with a color gamut of 101% NTSC (105.7% AdobeRGB). It means the Reference 21 can reproduce saturated basic colors (red and green in the first place) which are unavailable on ordinary monitors with the sRGB color gamut, i.e. 72% NTSC. The reproduction of colors that lie on the borders of the color gamut triangle (blue-green and yellow) is improved, too.

This property cannot be underestimated. In fact, monitors have one of the worst color gamuts among all devices for obtaining and displaying graphical information. Today’s scanners, cameras and camcorders have long gone beyond the scope of the sRGB color space, and high-quality typographic printing can easily handle yellow and green, too, although these colors are far from being pure on an sRGB monitor.

The pros and cons of the enhanced color gamut are better discussed on real-life examples. And I can do so, now that our lab has received a Samsung SyncMaster XL20, a monitor with LED-based backlighting.

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