In contrast to the ordinary TV, Digital TV or DTV uses the transmission in Digital format. Digital TV supports various types of picture formats of different combination size and interlacing. The digital format may be High Definition TV (HDTV) or Standard Definition TV (SDTV). HDTV transmission is in p720 (720 Progressive scanning) or i1080 (1080 interlace). Both use the 16:9 Aspect ratios. HDTV format cannot be transmitted through analog channels. SDTV on the other hand uses different formats based on different aspect ratio.
Digital TV signals can be received through the conventional antenna or through Digital cable or Digital satellite. In some parts, the signal is received by Microwaves while in some other parts; it may be through Internet protocol, DSL or Optical cable. The Peer-to-Peer (P2P) software can be used to see digital TV broadcast through computer. Some of the broadcast signals are Encrypted to avoid recording or misusing.
The video image in HDTV has high resolution of One Million Pixels per frame which is five times higher than the SDTV. HDTV transmits digital signals using the Video Compression technology. The Digital cable technology uses the video compression method developed by Motorola. Digital cable allows a number of channels to occupy frequency space for this compression technique used. Many cable providers can form two HD digital channels on a single analog channel frequency.
High Definition or HD is the top level resolution offered by the Digital TV technology. HD Format includes 1080 horizontal lines of vertical resolution. The formats of the Digital cable are Standard, Enhanced and High Definition. Standard format offers a resolution of 480i, Enhanced format offers 489p and the High Definition offers 720p and 1080i.
Progressive and Interlaced Scanning
HD TV is a high resolution TV system that gives more pixels on the screen to produce a clear picture. The standard resolution ratings of HDTV may be 1280×720(p720), 1920×1080(i1080), 1920×1080 progressive (p1080) etc. Here p stands for Progressive scanning and i stand for Interlaced scanning. Progressive is faster and less prone to blurring and is considered as the best possible resolution. The picture on the TV screen appears as many independently scanned lines. By combining all the lines, the picture image will be formed. For this, two methods like Interlaced and Progressive scanning methods are used. The resolution of the TV is defined by the lines and types of scanning. For example p720 means 720 progressive scanning and i1080 resolution has 1080 interlaced scanning lines. Side by side progressive scanning will give a clear picture than the interlaced scanning. Most of the HD TV programming is based on i1080 resolution.
The p1080 is generally referred to as Full HD since it has the ability to accept p1080 and display the same in a resolution of 1080 lines. The screen ratio of HD Television is around 1.78:1 and in Computers, the wide screen represents aspect ratio wider than 4:3 is considered as wider screen which is typically 16:9.
HD TV transmission occurs in the aspect ratio 16:9. This aspect ratio is often referred to as Wide Screen or letter box. Wide screen is the aspect ratio used in display devices. In cinema technology, wide screen means an image aspect ratio (width to height) is greater than 1.37: 1The standard HD TV has 4:3 aspect ratio while in wide screen TV it is 16:9. Wide screen aspect ratio gives 1920 pixels wide by 1080 high. This is similar to the 2K digital cinema technology. The Frame rate can be expressed as 1080p30 which means 30 progressive frames per second.
Display Resolution and Pixel
Display resolution refers to the number of distinct pixels displayed. It explains the physical number of columns and rows of pixels that creates the display. For example 1920 x 1080 pixels display. The term display resolution is applied in Plasma Display Panels (PDP), Liquid Crystal Display (LCD) and Digital Light Processing (DLP) devices. In order to display the image in the Fixed Grid of these devices, a Digital Video Processor called Scaling Engine in necessary in the device to handle the Multi format video signals. Pixel Density refers to the number of pixels per unit area or distance and not the total number of pixels. Pixel per Inch unit is used in Digital measurements. If the screen is 10 inches high, then horizontal resolution is measured across a square inch wide.
Eye perception and Resolution
The perception of image and the display resolution are important which is affected by factors like Image resolution and Optical resolution.
Image resolution typically describes how close lines can be each other. Line pairs are used instead of single lines for measurement. A line pair means a light line and adjacent dark line. For example a resolution of 10 lines per mm (10 LP / mm) means 5 light lines and 5 dark lines alternating each other. Image resolution is the details an Image holds which are measured in units like lines per mm, lines per inch etc. Optical Resolution is the ability of the Imaging system to resolve the details in the image. The Rectangular shape of the screen is also important. It is expressed as the ratio of the physical width to the height of the picture. This is determined by the aspect ratio. Displaying more information in a smaller screen will make the image more clear.