Your Guide To LCD Television

Progressive or noninterlaced scanning (or P-Scan) is a method for displaying, storing or transmitting moving images in which all the lines of each frame are drawn in sequence. This is in contrast to the interlacing used in traditional television systems where only the odd lines, then the even lines of each frame (each image now called a field) are drawn alternatively. With progressive scan, an image is captured, transmitted and displayed in a path similar to text on a page: line by line, from top to bottom. Progressive video is what your computer screen uses. The whole image is sent to the screen from top to bottom in one pass. This provides a more “stable” and natural looking image.

Comparison of progressive and interlace scanning

The advantages of progressive scan are:

• Higher vertical resolution than interlaced video with the same frame rate. The perceived vertical resolution of displayed video is traditionally adjusted using a Kell factor coefficient. This coefficient has no fixed value and depends on display device. Its value for interlaced video is usually lower than for progressive video, when the same display device is used. When interlaced video is compared to progressive video with the same number of scan lines, interlaced video delivers lower perceived vertical resolution at a lower frame rate.
• Absence of visual artifacts associated with interlaced video of the same line rate, such as interline twitter.
• No necessity in intentional blurring (sometimes referred to as anti-aliasing) of video to reduce interline twitter and eye strain. In the case of most media such as DVD movies and video games, the video is blurred during the authoring process itself to mask flicker artifacts when used on interlace displays. As a consequence, recovering the sharpness of the original video is impossible when the video is viewed progressively. An excellent, but rarely employed countermeasure to this is when display hardware and video games come equipped with options to blur the video at will, or to keep it at its original sharpness. This allows the viewer to achieve the desired image sharpness with both interlaced and progressive displays. An example of a video game with such a feature is Super Smash Bros. Melee, where a “Deflicker” option exists. Ideally it would be turned on when played on an interlaced display to reduce interline twitter, and off when played on a progressive display for maximum image clarity.
• Offers much better results for scaling to higher resolutions than equivalent interlaced video, such as up converting 480p to display on a 1080p HDTV. Scaling works well with full frames, therefore interlaced video must be deinterlaced before it is scaled. Deinterlacing can result in severe “combing” artifacts.
• Frames have no interlaced artifacts and can be used as still photos.

However, the only disadvantage of progressive scan is that it requires higher bandwidth than interlaced video that has the same frame size and vertical refresh rate.

Example of interlace scanning field

Interlaced scan refers to one of two common methods for “painting” a video image on an electronic display screen by scanning or displaying each line or row of pixels. This technique uses two fields to create a frame. One field contains all the odd lines in the image, the other contains all the even lines of the image. A PAL based television display, for example, scans 50 fields every second (25 odd and 25 even). The two sets of 25 fields work together to create a full frame every 1/25th of a second, resulting in a display of 25 frames per second.

The interlaced scan pattern in a CRT (cathode ray tube) display completes such a scan too, but only for every second line. This is carried out from the top left corner to the bottom right corner of a CRT display. This process is repeated again, only this time starting at the second row, in order to fill in those particular gaps left behind while performing the first progressive scan on alternate rows only.

Such scan of every second line is called interlacing. A field is an image that contains only half of the lines needed to make a complete picture. The afterglow of the phosphor of CRTs, in combination with the persistence of vision results in two fields being perceived as a continuous image which allows the viewing of full horizontal detail with half the bandwidth that would be required for a full progressive scan while maintaining the necessary CRT refresh rate to prevent flicker.

Interlace is a technique developed for improving the picture quality of a video signal primarily on CRT devices without consuming extra bandwidth (bandwidth is a cost, higher bandwidth require more data storage). Interlacing causes problems on certain display devices such as LCD TV. It was invented by RCA (Radio Corporation of America) engineer Randall C. Ballard in 1932, and first demonstrated in 1934, as cathode ray tube screens became brighter, increasing the level of flicker caused by progressive (sequential) scanning. It was ubiquitous in television until the 1970s, when the needs of computer monitors resulted in the reintroduction of progressive scan. Interlace is still used for most standard definition TVs, and the 1080i HDTV broadcast standard, but not for LCD, micromirror (DLP), or plasma displays; these displays do not use a raster scan to create an image, and so cannot benefit from interlacing: in practice, they have to be driven with a progressive scan signal. The deinterlacing circuitry to get progressive scan from a normal interlaced broadcast television signal can add to the cost of a television set using such displays. Currently, progressive displays dominate the HDTV market. Only CRTs can display interlaced video directly – other display technologies require some form of deinterlacing.

Broadly speaking, Progressive video will look better on an LCD TV because these panels are progressive in nature. Any Interlaced content is converted on the fly to Progressive (it ‘fakes’ a progressive picture, which never looks as good as a real progressive one).

1080p is the shorthand name for 1,080 lines of vertical resolution progressive scanning signal (1080 horizontal scan lines). The letter p acronym for progressive scan. 1080p can be referred to as Full HD (Full High Definition) to differentiate it from other HDTV video modes (example, HD Ready LCD TV). The term usually assumes a widescreen aspect ratio of 16:9, implying a horizontal resolution of 1920 pixels. This creates a frame resolution of 1920×1080, or 2,073,600 pixels in total. The frame rate in Hertz can be either implied by the context or specified after the letter p, such as 1080p30, meaning 30 Hz.

Common Video Resolutions (1080 / 720 / 480)

1080p is sometimes referred to in marketing materials as “Complete High-Definition”. However, 2K/4K digital cinema technology is commercially available, and ultra-high definition video is in the research phase.

In addition to the meaning of 1080p as a display resolution, 1080p is also used to describe video equipment capabilities. Use of 1080p and the closely related 1080i labels in consumer products may refer to a range of capabilities. For example, video equipment that up-scales to 1080p takes lower resolution material and reformats it for a higher resolution display. The image that results is different from the display of original 1080p source material on a native 1080p capable display. Similarly, equipment capable of displaying both 720p and 1080i may in fact not have the capability to display 1080p or 1080i material at full resolution. It is common for this material to be downscaled to the native capability of the equipment. The term “native 1080p capable” is sometimes used to refer to equipment capable of rendering 1080p fully.

Tags: 1080p, comparison, HDTV | Category: HDTV, LCD Article | Subscribe to comments | Leave a comment | Trackback URL