Understanding Monitor Specifications

Lecture Notes

Read on for an understanding of monitor specifications.

Introduction

Dot Pitch, Resolution & Refresh Rate

What is Dot pitch

Screen Resolution

Changing Screen Resolution

When buying a new monitor, what do we need to know? A typical monitor advert might look like-

Diamondtron

• 15.9-inch viewing area and .25mm dot pitch
• 1600 by 1200 maximum resolution at 70 Hz refresh rate
• 119 Hz maximum refresh rate at 1024 by 768 resolution
• Three-year warranty
• Price when ranked: $239

It appears we need to know about dot pitch, resolution, refresh rate and the meaning of screen dimensions. We will also need to know something about the difference between CRT, LCD and TFT monitors.

Dot Pitch, Resolution and Refresh Rate

Dot pitch, maximum screen resolution and refresh rate are important factors to consider when buying a monitor. If you buy a monitor without considering these factors you may end up with a substandard monitor or with an unsatisfactory display because screen resolution and refresh rate are not set appropriately.

What is Dot Pitch?

A monitor screen is made of of lots of tiny dots. Each dot is composed of a triad of phosphor cells - a red phosphor, blue phosphor and green phosphor cell.

In a normal cathode ray tube monitor (CRT) an electron gun at the back of the monitor shoots electrons at the back surface of the monitor screen. When electrons hit the phosphor cells they glow. The colour that each type of phosphor cell emits depends on the intensity with which electrons strike them. The red phosphor cell can be made to glow different intensities of red, the green phosphor cell can be made to glow different intensities of green and the blue phosphor cell can be made to glow different intensities of blue.

Each set of three phosphor cells make up a dot. The colour the whole dot appears to be depends on the intensity of the red phosphor cell, the green phosphor cell and the blue phosphor cell. You may recall mixing paints at school. This is similar except the three primary colours of light are red, green and blue.

Have a look at this RGB Application that shows you the colour produced when different combinations of red, blue and green light are mixed.

~Now try the activity~

Activity A

Using the RGB application, what colour do you get with the following colour combinations?

Red = 0, Green = 0 Blue = 0
Red = 255, Green = 255 Blue = 255
Red = 255, Green = 0 Blue = 0
Red = 255, Green = 255 Blue = 0
Red = 100, Green = 100 Blue = 100

So what is dot pitch?

Dot pitch is the distance in millimeters between each phosphor triad. Dot pitch is important because it is an indicator of image clarity and is a KEY element to consider when purchasing a monitor.

Sometimes a monitor specification will give the horizontal dot pitch, sometimes the diagonal dot pitch.

Typically. today's monitors might specify a dot pitch of between 0.22mm and 0.3mm. The smaller the number, the finer an image can be displayed on screen. A decent monitor should have a horizontal dot pitch of about 0.22 mm

If you know the dot pitch and size of the screen you can calculate the maximum resolution in pixels that can be displayed.

Screen Resolution

Now we know what a dot is. But what is screen resolution?

Screen resolution is the number of pixels across the screen and the number of pixels down the screen. E.g. 800 × 600 means there are 800 pixels across the screen and 600 pixels down the screen. But are pixels the same as dots?

Typically, monitor specifications include maximum resolution along with dot pitch. As an example, suppose we have a maximum resolution specified as 1600 × 1200, this means that there are 1600 dots across the screen and 1200 dots down the screen.

Provided the graphics card can handle it, an operating system can be configured to consider each single dot as a pixel and can draw the desktop colouring each pixel separately. In this case the desktop will be displayed at maximum resolution.

~~A pixel is the same as a dot at maximum resolution only~~

Now, although the number of dots a monitor has cannot be changed, the screen resolution can be changed. An operating system can be configured to consider groups of dots as pixels. As an example, suppose the screen resolution is changed from 1600 × 1200 to 800 × 600 . This means that each group of four dots is now considered to be a single pixel. Each set of four dots is now coloured identically.

~~So a pixel is a set of dots at a lower resolution than maximum~~

At maximum resolution each pixel is the same as a dot, otherwise a pixel is a group of dots.

Now, the lower the screen resolution the larger the text appears. The higher the screen resolution, the finer and smaller text appears to be. This is because the higher the resolution, the more pixels there are.

The pictures below show you two different screen resolutions.

High resolution display.

Set at 1152 × 864

Lower resolution display.

Set at 800 × 600.

Notice how the text and image appears larger

Changing Screen Resolution

You can change your screen resolution in Windows by going to Control Panel and double-clicking the Display icon. The Settings tab allows you to choose the screen resolution, the colour quality and in some cases, refresh rate.

Now when buying a monitor, you should note that standard resolutions include 640 × 480, 800 × 600, 1024 × 768, 1280 × 1024, 1600 × 1200. Have a look at some of the resolutions I can set my monitor to.

The maximum resolution you can expect from a monitor will depend on the size of monitor you are buying and the price you are prepared to pay. Most people today are content to set their screen resolutions to 800 × 600 or 1280 × 1024 although many people have other settings.

A 15" monitor should use a 640 x 480 or 800 x 600 resolution at least.
A 17" monitor may have a maximum resolution of 1280 x 1024, but 1024 x 768 gives a better screen ratio.
A 19" monitor may have a maximum resolution greater than 1280 x 1024, but at higher resolutions it can be difficult to read text on the screen.

Refresh Rate

The refresh rate of a monitor is really important. Every pixel on a screen is redrawn many times a second. This is to maintain the quality of the image. If flicker can be detected this will cause headaches and eye strain. Most people recommend a refresh rate of 75Hz (each pixel is redrawn 75 times a second.) Most monitors can be set to a higher refresh rate than this; 85Hz is another common refresh rate.

Now, at higher resolutions, there are more pixels to be redrawn. So if you increase screen resolution, you may notice that the refresh rate declines. Decreasing the refresh rate tends to allow a higher refresh rate. Imagine a see-saw.

High resolution ---- lower refresh rate

Low resolution ---- higher refresh rate

When buying a monitor, you should always check that the refresh rate can be set to 75Hz or higher at the resolution you prefer.

Monitor Dimensions

Monitor specifications commonly include screen size and viewable image size. These are different.

Screen size is measured from one corner of a screen diagonally to the other corner. Typically, screens come in 15", 17", 19" and 21" sizes. The greater the size the more expensive the monitor will be.

The viewable area is the diagonal distance from one corner to another of the glass, not including the black border. This size will be smaller than screen size. Typically a 15" monitor will have a viewable image size of 13.9".

A few years ago 15" monitors were common. However, after major decline in cost and advance in quality, 17" monitors are becoming more common. Also available are 19", 21" and even 24" monitors

Monitor Types

For many years, the only choice of monitor was a cathode ray tube type (CRT.) CRT technology is similar to a television set.

Laptops used a different screen technology - liquid crystal displays (LCD).

These days you can also buy a LCD flat panel monitor for your desktop computer

LCD monitors have the advantage of low radiation emission, compactness and portability. However, they are expensive compared to CRT monitors. Also, they have a limited viewing angle. If you look at a LCD monitor from an angle then the brightness and colour depth drops and it takes on a hazy appearance.

This is because of the way light reflects off a LCD screen.

There are now other alternatives to CRT and LCD monitors in the form of TFT (thin film transistor) monitors. These are similar to LCD monitors with similar advantages but again they are expensive and have a limited viewing angle. LCD and TFT monitors are limited in the resolutions you can set them to. For an optimum display it is best to leave the display settings on the factory defaults. These monitors are not particularly suitable for gaming or for use with CAD draughting or other graphics applications.

Graphics Cards

A monitor needs to be connected to a graphics card plugged into the computer's motherboard. The graphics card controls the operation of the monitor.

You should be aware that monitor display is at the mercy of your graphics card.

The resolution you can set your monitor to will depend upon the quality of your card. You may have a fantastic 21" monitor capable of displaying images at 1600 × 1200 screen resolution but if the graphics card is old you may end up with a much lower resolution setting.

Some inexpensive graphics cards are often capable of delivering what the monitor needs to live up to its full potential. However, in some cases substandard monitor performance can result from old or poor quality graphics cards. Today, AGP graphics cards tend to be chosen over PCI graphics cards for the higher performance they can deliver.

That is folks!!