HDTVs support video at resolutions up to 1920-by-1080 pixels, providing a crisper image than 640-by-480 standard definition video. If your video source is connected improperly, however, your video might not run in high definition, causing it to look blurry and not fit the screen correctly. Other quality issues can arise from improperly set options.
Loose or improperly connected cables can cause your TV to not work or display images incorrectly, so the first step in troubleshooting is to check all your connections. In addition to the power cable on your HDTV, it should have a connection to every input device, such as your cable box, satellite receiver, game console and Blu-ray player. These connections use a variety of cable types, including HDMI, coaxial, component and composite. When attaching component or composite cables, match the cable colors to the port colors on your TV. Component cables have two red ends -- one for video and one for audio. Most cables group the red audio cable closely with the white audio cable to help you tell them apart. Once connected, make sure you set the "Input" or "Source" on your TV to the correct input for the device you're trying to watch.
Viewing HD Video
Displaying video in HD quality requires several components in addition to an HDTV. First, your source must support HD output. For example, when watching cable TV, you need a subscription that includes HD and a cable box that can receive it. You also need to watch an HD channel; many channels still broadcast in standard definition. Finally, you have to use either an HDMI cable or component cables. Coaxial, composite and most other connections on TVs do not support HD. VGA and DVI inputs do support HD, but are generally only used for plugging in computers.
Stretching SD Video
Even on an HDTV, you'll still end up watching some channels and devices -- such as older game consoles -- in standard definition. As SD video uses a different aspect ratio than HD video, HDTVs offer multiple settings for scaling the image, some of which can make the image look worse. Specific settings vary by model, but in general you can choose to retain the original ratio by adding black bars (known as letterbox mode) or by stretching the image in a variety of shapes. Stretching the image results in either cutting off part of the picture or altering its shape, so try changing between options until you find one that looks best on your screen.
Changing TV Settings
Using your TV's onscreen menu, you can change settings for how the screen displays images. Every brand and model has different settings, but most offer similar features. For example, if the colors look wrong, try tweaking the brightness, contrast, saturation or color temperature. There's not one "right" way to set these options, so adjust them until they look good to you. If you see outlines around objects on screen, especially on thin lines and text, turn your sharpness down. Though it seems counter-intuitive, a high sharpness setting can actually distort the image and make it look worse. Some TVs also allow you to change audio settings, such as the bass and treble levels.