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.

What the different of LCD and Plasma technology?
Plasma and LCD panels may look similar, but the flat screen and thin profile is where the similarities end. Plasma screens, uses a matrix of tiny gas plasma cells charged by precise electrical voltages to create picture. While LCD screens, as it name suggests, liquid crystal display are liquid crystal sandwiches between two glass panel. Again, electrical charge voltage applied to varying the liquid crystals. Plasma TV have slightly edge over LCD in term of black color display, which mean better contrast and detail in dark-colored movie scenes. The LCD technology, light source from CCFL (Cold Cathode Fluorescent Light) or white LED (latest version) shines through crystals panel and glasses layer, hard to achieve perfect black color because there is alway some light leakage in between pixels. Manufacturer keep improving with new technology and manufacturing advancement from generation to generation. Apart from better contrast with better ability to show perfect black, plasma screens do have wider viewing angles than LCD screens. Viewing angle mean how far you can sit on either side of screen before the image of screen disappear.

Samsung LED backlight Full HD LCD TV

For LCD screen, some brightness and color shift happen when viewing angle is high (far from center of screen). Plasma screen have better viewing angle compare to LCD screen. Manufacturer are improving the lagging of LCD screen technology to catch up with Plasma screen technology, and steadily changing with more and better LCD screen technology entering the market, where now the viewing angles of some model of LCD screen is equal or better then plasma screen. Plasma produce brighter color too, compare to LCD screen due to light leakage on LCD between pixels that affecting its color saturation.

Advantages of Plasma over LCD technology
LCD screens tend to has blur images in fast moving scenes in action movie or sport due to slow switching time of crystals from black to white. While this was true for older generation LCD screens, new models have improve significantly and close the gap between these two technology. The lowest the switching time for LCD, the better the image quality in fast moving scenes. Currently there is some manufacturer claim their LCD TV switching time as low as 2ms, while typically 6ms switching time will provide good fast moving scenes. Another advantage of Plasma is low price for screen size larger than or equal to 42-inch. This has changed recently where LCDs’ price for screen size of above 42-inch are matching or even beating plasma in both resolution and price.

Advantages of LCD over Plasma technology
Apart from being price competitive, LCD has the edge over plasma in several other key areas. LCDs tend to have higher native resolution than plasmas of similar size, in layman term, it mean more pixels on same area of screen. LCDs also consume less power than plasma screens with estimated power saving of more than 30 percents. Except for greener for LCD technology, it weight lighter than similar sized plasma TV and making it more feasible to mount on wall. The lifespan of LCD TV out-perform plasma TV where plasma screen would lose half of their brightness after more than 20,000 hours of viewing. While almost all LCD TVs have lifespan of 60,000 hours or more. However, newer version of plasmas have bumped up that lifespan to between 30,000 and 60,000 hours. Plasma TV prone to screen burn effect if static image left display on screen too long and resulting the ghost of image burned in permanently to plasma screen. Newer plasma TV less susceptible to this with improved technology. LCD screen do not suffer from this due to the picture is display via changing crystals.

LCD or plasma the mainstream technology in market today?
Currently only 3 manufacturer continue to roll out new models of Plasma TV, there are Panasonic, Pioneer and Hitachi. For LCD TV, there are tones of manufacturer and the price had drop more than 15 percents year-on-year. If you look for better resolution, go for LCD TV. If you prefer big screen size with good image quality, but not on resolution, Plasma is the right choice for you. Today LCD TV manufacturer drive full HD (High Definition) as the selling point to fight Plasma TV, but now new version of Plasma TV do support 1080p high resolution. Despite the current HD buzz, the content available in 1080p is still very little and you are paying the premium price of Full-HD for future, not tmorrow.