Snake Oil, Miracle Cures, and Computer Monitors

So you think you are ready to buy one of those really hi-res monitors that you've been hearing about. Your graphics display adapter can produce those high resolutions, and now you're ready for a monitor to match it.

It might come as a surprise to you that there are relatively few monitors capable of fully resolving some of the higher resolutions. So before making a purchase, read the text below to find out what I learned, and consult the Monitor specifications table, then perhaps do a little research of your own, and contribute what you've learned to this document.

Another source of possibly useful information is an article printed in Computer Shopper recently. While I don't agree with the author of that article on a couple of points, I think he is probably right about "dot pitch" being measured on a direct line between phosphor centers. I'll have to edit my document again when I get the chance.

Separating Fact from Fiction

Most manufacturers make claims like ``Maximum Resolution: 1280x1024''. This is usually not a measure of the maximum number of unique dots that can be displayed, but rather a measure of the maximum speed of the video signal, also know as the ``Bandwidth''. Most monitors are actually capable of displaying an image at the advertized resolution, but you will not be able to identify individual pixels on the display. The reason is that more than one pixel will be illuminating a phosphor location (color dot) on the screen.

Video bandwidth is only one of several factors that contribute to the maximum resolution of a display. The physical size of the display, plus the size of the pixels on the display are also important, and harder to achieve than the signal speed.

A little looking at the local computer store will show that no two 17-inch monitors are quite the same. They certainly don't have the same diagonal measurements for the viewing area of the monitor. Although most manufacturers ``exaggerate'' the diagonal measurement of their displays, they are a little more honest when specifying the width and height of the ``active display area'' available. This information is usually found in the back of the owners manual on the ``Specifications'' page. If you ask nicely, most salespeople will try to find the owners manual that came with the display model for you to look at. Alternatively, you can call the manufacturer directly for this information.

On that same page, you will usually find another useful tidbit of information: the ``dot pitch'' of the monitor. On monitors with a Trinitron tube, this is sometimes called ``effective dot pitch'' or ``slot mask size''. You may find that this number is a little larger than the one the salesman told you, or that was written on the outside of the box. This number is a measure of the size in millimeters (and by relation, the frequency) of the dots on the screen of the monitor.

So just what do these numbers mean? If you divide the width of the active display area by the dot pitch, you get the maximum number of distinct horizontal dots you can display. Likewise, if you divide the height by the dot pitch, you get the maximum number vertical dots. The following table shows some popular resolution values and the display sizes needed at various popular dot pitch sizes.

	Display sizes for Various Resolutions of display
		Xmm x Ymm = real-diagonal-inches*

dot  |
pitch|  1280 x 1024       1152 x 900        1024 x 768        800 x 600
------------------------------------------------------------------------------
0.25 | 320 x 256 = 16.8  288 x 225 = 14.8  256 x 192 = 12.6  200 x 150 =  9.9
0.26 | 333 x 266 = 17.5  300 x 234 = 15.4  266 x 200 = 13.2  208 x 156 = 10.3
0.27 | 346 x 276 = 18.2  311 x 243 = 16.0  276 x 207 = 13.7  216 x 162 = 10.7
0.28 | 358 x 287 = 18.9  323 x 252 = 16.6  287 x 215 = 14.2  224 x 168 = 11.1
0.29 | 371 x 297 = 19.5  334 x 261 = 17.2  297 x 223 = 14.7  232 x 174 = 11.5
0.30 | 384 x 307 = 20.2  346 x 270 = 17.8  307 x 230 = 15.2  240 x 180 = 11.9
0.31 | 397 x 317 = 20.9  357 x 279 = 18.4  317 x 238 = 15.7  248 x 186 = 12.3

* diagonal measurement assumes a 4x3 image aspect ratio

Based upon this table, we can see that no manufacturer is going to be offering a 17-inch monitor which can actually achieve a 1280x1024 display resolution. While a 0.25 dot-pitch 17'' monitor might squeak it out, the temptation to call the monitor 18'' or 19'' (to help justify the price being higher than other 17'' monitors) would be just too great for even the most saintly marketing director.

Now that you understand some of the numbers involved, take a look at the Monitor specifications table.

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Copyright @ Р. Кожухаров    Последно обновена: Ноември 28, 2005    09:52:42