X-bit labs

X-bit’s Guide: Contemporary LCD Monitor Parameters and Characteristics (page 5)

Category: Other

by Oleg Artamonov

[ 10/26/2004 | 02:58 PM ]

Viewing Angles

Yet another traditional problem of the LCD monitor technology is the angle you are permitted to look at the screen at. While the image on a CRT screen looks practically the same whatever your line of sight is, a small deflection from the perpendicular leads to a dramatic degeneration of contrast and color reproduction with many LCD matrices.

Meanwhile, all the manufacturers are now declaring seemingly acceptable viewing angles – the majority of monitors have 160° viewing angles both ways – horizontal and vertical. The problem is – like with the response time – how these angles are measured.

According to the current standards, the matrix manufacturers define the viewing angle as the angle relative to the normal dropped to the center of the matrix – when viewed at this angle, the contrast ratio in the center of the matrix degenerates to 10:1. This definition makes room for some pitfalls an unsuspecting user may get into.

First, it is known that the image becomes apparently distorted when the contrast ratio degenerates just in a few times, i.e. to about 100:1. In other words, the method the manufacturers employ is rather lax, and this is enough to be skeptical about the specified viewing angles, since you’ll most likely notice the deflection from the ideal picture at much smaller angles. Furthermore, some manufacturers specify viewing angles for a contrast ratio of 5:1 rather than 10:1, thus making the angles of an inexpensive TN+Film matrix wider like 160/160 degrees instead of 150/140. Of course, this “modernization” gives nothing to the user – the matrix remains the same, although the specifications seem to say that the manufacturer of the monitor has started using new matrices with wider viewing angles, and only a small text at the bottom of the package tells you that it is only the measurement method that has actually changed.

Second, the contrast ratio is measured in the center of the screen, while the user sees the sides of the screen at a different angle than the center. For example, the next snapshot depicts a Greenwood LC521FT monitor and the camera is looking at it from below, at a small angle:

You are wrong if you think the monitor’s screen background is a gradient from black at the top to gray at the bottom. The monitor is actually displaying an absolutely even gray background of the color RGB:{128;128;128}, while this striking discrepancy in the brightness between the top and bottom of the screen is due to the insufficiently wide vertical viewing angle. However, the brightness in the center of the screen is much closer to the ideal than at the top of the screen (which seems almost purely black), and the standard method of measuring the viewing angles will give us a high enough contrast ratio as not to consider a vertical angle of 25 degrees as a limit (that’s the angle at which the camera is looking at the screen).