HD offers the highest resolution picture available for the home.
The picture you see on your TV screen is made up of hundreds of horizontal lines. Each of the lines is built-up by a large number of pixels. In Standard Definition (SD) television the picture is made up of 576 lines whereas in High Definition (HD) television the picture is made up of either 720 or 1080. TV’s generally display pictures at the resolution set by the source. Resolution is described in terms of ‘number of lines of resolution’ or number of pixels. Both horizontal and vertical resolutions need to be considered for video signals. But for display screens, it is the vertical resolution that is more noticeable to the human eye.
The clarity and colour reproduction in HD images are almost entirely down to the increased resolution levels. HD provides more than four times more information than comparable SD screen; and because HD holds more information, it lends itself to being shown on larger screens. HD also has the advantage of being delivered in widescreen (16:9) format as well as high resolution multi-channel audio. This means that it offers you truly superb picture quality, clarity and colour definition along with fantastic sound.
HD picture resolution is described by a number of terms – 720p, 1080i, 1080p. But what do these terms mean? Each of them provides high quality images but they differ slightly. This combination of a number and letter refers to the number of vertical lines of resolution and whether the signal is interlaced (i) or progressive (p).
HD picture resolution is also often listed as ‘1920 x 1080 pixels’ or ‘1280 x 720 pixels’. The first number refers to the horizontal resolution and the second number refers to vertical resolution. Multiplying the two together gives you the total resolution of the screen. More pixel means better resolution and finer detail.
Interlaced (i) & Progressive Scan (p)
The images you see on a screen are formed by horizontal lines called scan lines; simply put, the more lines you have, the clearer the picture. It is the way these lines appear on screen which differs between progressive and interlaced.
Up until recently television broadcasts in this country had always been an interlaced signal. However HD television allows for both progressive and interlaced signals.
Interlaced
With an interlaced signal the scan lines are split into two sets. One set contains the even numbered lines while the other contains the odd numbered lines. The screen will scan the first set of lines, then the second. It does this roughly 50 times a second, 25 times for each set. This effectively gives you 25 complete frames per second. This method makes the picture a little less clear when an object is moving quickly on the screen and not particularly good for motion, but has the edge on resolution.
Progressive
Progressive had traditionally been used in DVDs and computer monitors. But with the dawn of HD, progressive scan became an option in broadcasting as well as for other HD sources.
Progressive is also formed of a number of horizontal lines. In this case each frame is drawn in sequence, rather than splitting the frame up into alternate parts. This method provides for smoother motion and crisper images, especially when displaying movement.