When it comes to picture quality, distortion is the enemy. Every time you upscale or downscale an image, you're taking an educated guess as to where each dot should be on the screen. You're also taking the risk of introducing, or amplifying, imperfections in the image. The same happens when you distort the picture by zooming or changing the aspect ratio.
Even if you set your source (such as a Blu-ray player or HD PVR) to the native aspect ratio of your television, for example 1920x1080p, there's probably still some distortion occurring. The television or the player could be introducing overscan, which makes the picture slightly larger than the display to trim any recalcitrant pixels on the edge of the picture.
Some televisions let you disable any overscan or other distortion by enabling a feature called 1:1 pixel mapping. The setting displays the input source without scaling it, so that each pixel received is mapped to a single native pixel on the screen. There's no guesswork involved.
Full Pixel Mode and Dot by Dot
Different vendors have different names for this setting, for example Sony calls it Full Pixel mode while Pioneer calls in Dot by Dot. Sometimes it's not visible in the menus unless an appropriate source is attached.
When 1:1 pixel mapping comes in handy
1:1 pixel mapping is particularly useful if you're hooking up a media centre PC, as most high-end graphics cards offer a lot of flexibility over the output settings. It's also handy if you want to compare the 1080 upscaling on your player to the upscaling on your television.
You should also ensure the aspect ratio on your television is set correctly - if you're viewing a widescreen 1080p image the correct setting is probably called "Full". Any setting that use the word Zoom is stretching and scaling the image, to the detriment of the image quality.
There might be times when overscan and scaling are appropriate, but at least 1:1 pixel mapping gives you a choice.
Buying a flat screen TV? Have a question you'd like us to answer? Add your comments or questions about flat screen TV issues to the discussion below.
Also in this series, How to Pick a Great Flat Screen TV, And Not Get Sucked In By Marketing Hype:
Part 9: video inputs and future proofing
Part 8: Logitech Harmony vs AV Link remote controls
Part 7: Should you upgrade your TV for DLNA?
Part 6: TV tuners and "Digital Capable"
Part 5: HDMI and component ports
Part 4: LED and backlighting
Part 3: Screen size
Part 2: Refresh rates
Part 1: Brightness and contrast ratios
Also see our 5 tips for buying a digital TV set top box
And also see the lowdown on Freeview, and whether you should care
If you're new to Digital TV, or have yet to make the leap, start by reading Prepare yourself for Digital TV