High Definition CCTV Systems
High definition television (HDTV) has much more number of lines of resolution and produces better quality image by about 2 to 5 times than standard television. Resolution is defined as number of horizontal pixels x number of vertical pixels, for example 1280 x 720 or 1920 x 1080. Often the number of horizontal pixels is implied from context and is omitted.
The resolution number is appended with i or p; the lower-case i denotes interlaced and the lower-case p progressive. With the interlaced scanning method (when the notation is 1080i), the 1,080 lines of resolution are divided into pairs. The first 540 alternate lines are painted on a frame and then the second 540 lines are painted on a second frame. The progressive scanning method (when the notation is 1080p) simultaneously displays all 1,080 lines on every frame with better quality pictures, requiring greater bandwidth.
The notation can also be appended with scanning rate like 1080i60, 1080p30, or 720p60. The numbers after i or p are scanning rate per second. For commercial naming of a product, the frame rate is often dropped.