Screen Resolution? Aspect Ratio? What do 720p, 1080i & 1080p Mean?

In days gone by, screen resolution (also called display resolution) wasn’t much of an issue. Windows came with a few preset options, and to get higher resolution or more colors (or both) you would install a driver for your video card. As time went on, you could choose better video cards and better monitors as well. Today we have lots of options when it comes to displays, their quality and the supported resolutions. In this article I would like to take you through a bit of history and explain all the important concepts.

It all started with IBM & CGA

The color graphics technology was first developed by IBM. CGA was first, followed by EGA and VGA--color graphics adapter, enhanced graphics adapter, video graphics array. Regardless of the capability of your monitor, you’d still have to choose from one of the few options available through your graphics card’s drivers. For the sake of nostalgia, here’s a look at a once well-known CGA display.

CGA  display

With the advent of high definition video and the increased popularity of the 16:9 aspect ratio (I’ll explain more about aspect ratios in a bit) selecting a screen resolution is not the simple affair it once was. However, this also means that there are a lot more options to choose from, with something to suit almost everyone’s preferences.

Let’s look at what today’s terminology is, and what it means.

The screen is what by what?

I am sure some of you already know that the term "resolution" isn’t correct when it’s used to refer to the number of pixels on a screen. That says nothing about how densely the pixels are clustered. "Resolution" is technically the number of pixels per unit of area, rather than the total number of pixels. Here, I’ll be using the term as it’s commonly understood, rather than the absolutely technologically correct usage.

Since the beginning, resolution has been described (accurately or not) by the number of pixels arranged horizontally and vertically on a monitor, for example 640 x 480 = 307200 pixels. The choices available were determined by the capability of the video card, and they differed from manufacturer to manufacturer.

The resolutions built into Windows were very limited, so if you didn’t have the driver for your video card you’d be stuck with the lower-resolution screen that Windows provided. If you’ve watched Windows Setup or installed a newer version of a video driver, you may have seen the 640 x 480 low resolution screen for a moment or two. It was ugly even on CGA screens, but that was the Windows default.

As monitor quality improved, Windows began offering a few more built-in options, but the burden was still mostly on the graphics card manufacturers, especially if you wanted a really high resolution display. The more recent versions of Windows can detect the default screen resolution for your monitor and graphics card and adjust accordingly. This doesn’t mean that what Windows chooses is always the best option, but it will work, and you can change it if you wish, after you see what it looks like. (I will talk about this in a future article.)

CGA  display

Mind your P’s and I’s

You may have seen the screen resolution described as something like 720p or 1080i. What does that mean?

To begin with, the letters tell you how the picture is "painted" on the monitor. A "p" stands for progressive, and an "i" stands for interlaced.

The interlaced scan is a holdover from television and from early CRT monitors. The monitor or TV screen has lines of pixels arranged horizontally across it. The lines were fairly easy to see if you got up close to an older monitor or TV, but nowadays the pixels on the screen are so small that they are very hard to see even with magnification. The monitor’s electronics "paint" each screen line by line, too quickly for the eye to see. An interlaced display paints all the odd lines first, then all the even lines.

Since the screen is being painted in alternate lines, flicker has always been a problem with interlaced scans. Manufacturers have tried to overcome this problem in various ways. The most common way is to increase the number of times a complete screen is painted in a second, which is called the refresh rate. The most common refresh rate was 60 times per second, which was acceptable for most people, but it could be pushed a bit higher to get rid of the flicker that some people perceived.

As people moved away from the older CRT displays, the terminology changed from refresh rate to frame rate, because of the difference in the way the LED monitor works. The frame rate is the speed with which the monitor displays each separate frame of data. The most recent versions of Windows set the frame rate at 60 Hertz, or 60 cycles per second, and LED screens do not flicker. And the system changed from interlaced scan to progressive scan because the new digital displays were so much faster. In a progressive scan, the lines are painted on the screen in sequence rather than first the odd lines and then the even lines. If you want to translate 1080p for example, is used for displays that are characterized by 1080 horizontal lines of vertical resolution and a progressive scan.

There’s a rather eye-boggling illustration of the differences between progressive and interlaced scans on Wikipedia here: Progressive scan. For another interesting history lessons, read also Interlaced video.

What about the numbers: 720p, 1080i and 1080p?

When high-definition TVs became the norm, manufacturers developed a shorthand to explain their display resolution. The most common numbers you will see are 720p, 1080p and 1080i. As we’ve seen, the "p" and "i" tell you whether it’s a progressive-scan or interlaced-scan display. And these shorthand numbers are sometimes used to describe computer monitors as well, even though in general a monitor is capable of a higher-definition display than a TV. The number always refers to the number of horizontal lines on the display.

Here’s how the shorthand translates:

  • 720p = 1280 x 720 (16:9 aspect ratio)
  • 1080p = 1920 x 1080 (widescreen display -16:9 aspect ratio)
  • 1080i = 1920 x 1080 (widescreen display -16:9 aspect ratio)

What is the Aspect Ratio?

At the beginning I mentioned the term aspect ratio. This was originally used in motion pictures, indicating how wide the picture was in relation to its height. Movies were originally in 4:3 aspect ratio, and this carried over into television and early computer displays. Motion picture aspect ratio changed much more quickly to a wider screen, which meant that when movies were shown on TV they had to be cropped or the image manipulated in other ways to fit the TV screen.

As display technology improved, TV and monitor manufacturers began to move toward widescreen displays as well. Originally "widescreen" referred to anything wider than the common 4:3 display, but it quickly came to mean a 16:10 ratio and later 16:9. Nowadays, nearly all computer monitors and TVs are only available in widescreen, and TV broadcasts and web pages have adapted to match.

Until 2010, 16:10 was the most popular aspect ratio for widescreen computer displays. But with the rise in popularity of high definition televisions, which were using high definition resolutions such as 720p and 1080p and made this terms synonyms with high-definition, 16:9 has become the high-definition standard aspect ratio.Today, finding 16:10 displays is almost impossible.

Depending on the aspect ratio of your display, you are able to use only resolutions that are specific to its width and height. Some of the most common resolutions that can be used for each aspect ratio are the following:

  • 4:3 aspect ratio resolutions: 640×480, 800×600, 960×720, 1024×768, 1280×960, 1400×1050, 1440×1080 , 1600×1200, 1856×1392, 1920×1440, and 2048×1536.
  • 16:10 aspect ratio resolutions: - 1280×800, 1440×900, 1680×1050, 1920×1200 and 2560×1600.
  • 16:9 aspect ratio resolutions: 1024×576, 1152×648, 1280×720, 1366×768, 1600×900, 1920×1080, 2560×1440 and 3840×2160.

How does the size of the screen affect resolution?

Although a 4:3 TV’s display can be adjusted to show black bars at the top and bottom of the screen while a widescreen movie or show is being displayed, this doesn’t make sense with a monitor, so you’ll find that Windows will not even offer you the widescreen display as a choice. You can watch movies with black bars as if you were watching a TV screen, but this is done by your media player.

The most important thing is not the monitor size, but its ability to display the higher resolution images. The higher you set the resolution, the smaller the images on the screen will be, and there comes a point at which the text on the screen becomes so small it’s not readable. On a larger monitor it is possible to push the resolution very high indeed, but if that monitor’s pixel density is not up to par, you won’t get the maximum possible resolution before the image becomes unreadable. In many cases the monitor will not display anything at all, if you tell Windows to use a resolution the monitor cannot handle. In other words, don’t expect miracles out of a cheap monitor. When it comes to high-definition displays, you definitely get what you pay for.

Conclusion - It’s is all a confusing mess

If you are not very technical, it is very likely that you are confused by so many technicalities. Hopefully this article has managed to help in your understanding of the most important characteristics of a display: aspect ratio, resolutions or type. I won’t stop here however. In the next article - How to Change Your Display’s Screen Resolution & How to Make Text & Icons Bigger, I talk about how you can change your display resolution so it works best for you.

Related articles:

Why & How To Calibrate a Monitor in Windows 7
How to Install a Color Profile
How to Set Up a Digital Photo Editing Environment in Windows