BenQ FP781 Display errors, Pixel errors, Blurred image, Multifrequency as opposed to Multiscan

Benq LCD Color Monitor User's Guide

Display errors

A. Pixel errors

Pixel errors are (unfortunately) unavoidable with today's production methods, if you want to man- ufacture displays at an economically sensible price.

A display with a resolution of 1024x768 dots therefore has 786432 pixels. Each pixel consists of the three sub-pixels for red, green and blue. That makes 2,359,296 individual control transistors. It can occur during production that one or several transistors is defective, which means that pixel errors occur, in which a sub-pixel does not light up at all or does so all of the time.

If you were to accept the same error rate as in the case of the strip mask, for which two horizontal lines are completely disrupted, then you would end up with a 2.6 percent error rate. The accepted error rates for LC displays are far lower, however. If, for example, you were to accept a tolerance of three permitted pixel errors per display, the you would end up with an error rate of 0.0038 per thousand.

B. Blurred image

You can also end up with blurred images with LC displays indeed whenever you depart from the native resolution. A display is built for a set resolution, smaller resolutions can only be displayed interpolated. If, for example, you want to display a resolution of 800x600 on a display with a native resolution of 1024x768, then each horizontal dot would have to display 1.28 dots of the resolution. This doesn't work of course and so intermediate values are calculated and this distorts the original image.

C. Multifrequency as opposed to Multiscan

LC displays require a digital control and because currently there is still no valid standard for a digital control, for the sake of compatibility there is a tendency to revert to the standard VGA connec- tion. This is also ideal for monitors, as they require an analog signal.

The image digitally created in the computer is converted in the graphics card into an analog signal and thus directly controls a CRT monitor. If, however, you use the analog signal of the VGA connec- tion for a digital LC display, then transducer electronics at the input of the display must cater for conversion back into digital signals. Two problems occur with this:

1. conversion losses:

The image is not so optimal as compared with direct, digital control. It can otherwise be the case that subsequent adjustments are necessary every couple of months on a regu- lar basis. This is generally executed via the OSD or an automatic function)

2. Limitation to specific operating modes:

Nowadays A CRT monitor is usually a multiscan monitor, which means it can be operated within the limits of its horizontal and vertical frequency, even in non-standard modes. An LCD monitor, in contrast, is a multi-frequency monitor, which means it is only guar- anteed to work together with specific modes (see list in the user's guide).

English 51