Buying a TV? Be sure you know what 720p, 1080p, 1080i and native resolution mean

November 30, 1:30 PMGadgets ExaminerDan Appleman

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The native resolution is the actual number of pixels that
can be displayed on the TV

Resolution. It’s probably one of the most important features to consider when shopping for a new TV. There is the question of 720p vs. 1080p vs. 1080i. And what is the difference between those and the native resolution of the set? Here’s a quick tutorial to help you navigate your choices and choose the set that’s best for you.

A TV screen is made up of color dots (take a magnifying glass to one and you’ll see them). These dots are called pixels. The number of horizontal pixels by vertical pixels built into the display is called the native resolution of the display. This is expressed as horizontal x vertical (for example: 1920x1080). The vertical resolution is the same as the number of “lines” on the display (a historical reminder of the days when CRT based TV’s scanned lines from top to bottom). Typical native resolutions you’ll find are:

• 852x480 (DVD quality)
• 1366x768 (Used in 720p sets)
• 1280x 720 (Used in 720p sets)
• 1920x1080 (Used in 1080i and 1080p sets)

On a 1080i (interlaced) signal, the odd (green)
lines are drawn, followed by the even (red) lines.
The entire screen is updated 30 times per second

When we talk about 720p, 1080i and 1080p, we’re really talking about the input signal. What do these three numbers mean?

480p – The TV “draws” 480 lines of video 60 times a second.

720p – The TV “draws” 720 lines of video 60 times a second.

1080p – The TV “draws” 1080 lines of video 60 times a second.

1080i – The TV first draws 1080 lines of video 30 times a second, dividing it into two groups of 540 lines that are interleaved (in other words, the signal first draws the odd line numbers, then the even line numbers).

Here are the key facts you need to know before deciding on a set:

• Faster refresh rate makes a picture look better when there is lots of action. Thus progressive (p) will tend to look better than interlaced video (i) when there is lots of motion on the screen
• Your eye can only see so much resolution. That’s why they don’t put 1920x1080 pixels on an IPod. On mid size TV’s (under 46 inches), you’ll have a hard time telling the difference between 1280x720 and 1920x1080
• Broadcast HD is either 720p or 1080i. Why? Because bandwidth – the amount of data transferred each second, has a cost. A 720p signal has to transfer 55 million pixels/second of data. A 1080i signal has to transfer 62.2 million pixels/second of data. A 1080p signal has to transfer 124.4 million pixels/second of data. That’s a big difference.
• Why get 1080p? Your Blu-Ray player or video game system can often output 1080p signals for the best possible quality video.
• There is no benefit to having an input signal is higher than the native resolution of the TV. If you plug a 1080i signal into a 1280x720 resolution TV, you’ll see 1280x720 video. The TV down converts the signal to the native resolution of the TV.
• There is no benefit to having a native resolution greater than your input signal. Playing a 480p standard DVD on a 1920x1080 TV won’t magically give you extra pixels (though advanced video algorithms will do their best to give you a good image when it scales up).

Now that you know these facts, the decision on which TV to get is really a lot easier.

For smaller and mid-sized sets – anything up to 42 inches, a 1280x720 or 1366x768 set is fine – unless you plan to also use the set as a computer monitor! In that case, get 1080p and the highest native resolution you can find and be sure to get a VGA or HDMI input (most sets these days have them).

For mid-size sets in the 40-50 inch range, again either one should be fine. Unless you look very carefully, you will not see a difference. Most sets in this range can accept both 720p and 1080i or p input. If you’re an avid gamer, consider going to the higher native resolution and 1080p. Newer sets in this size range are almost all 1080p.

For larger sets resolution starts to matter. Go with a 1920x1080 resolution with 1080p input. If you’re going that large, you can afford a few extra dollars to have it look its best on Blu-Ray and video games. Again, most newer sets in this range are 1080p.