Your Home Theater System Bible

Advantages and Disadvantages of Interlaced Scan Signal

interlaced program scanDifferent types of television sets, uses different program scan signal, thus projects varied images whenever a program is shown on the screen. A flicker or an alteration of the images may be present when the signal projected is drawn by a bandwidth conservative pulling interlaced scan signal.

Once you see video formats as 480p or 720p, the numerical value designates just how many horizontal lines of resolution the video signal uses, while the letter “p” indicates it is a progressive scan signal, hence 480p would just mean 480 horizontal lines of resolution with progressive scan. Correspondingly, the 1080i scan signal format confines 1080 lines of resolution that are interlaced. Both 720p and 1080i are used by HDTV.

There are a couple of methods by which video images may be displayed or projected on the image display devices. It could either be through an interlaced scan or through a progressive scan.

Progressive scanning, which is also referred to as non-interlaced scanning, was initially known  as “sequential scanning,” is an electronic image display device stores, presents as well as transmits moving images in which all the lines of each frame are drawn in sequence.

An interlaced scan signal, on the other hand, is another way in which images are projected since the invention of the television, and are designed exclusively for the large Cathode Ray Tube (CRT) televisions. With the interlaced scanning method, a TV draws images in an alternating fashion. In order to display an image, the television sequentially draws all of the odd numbered lines from top to bottom and then proceeds to fill in the even lines. This process occurs at a rate of 30 frames per second, which means that the entire process only takes around 1/30 of a second. With the interlace program scanning method, the image quality of a video signal is improved with no extra bandwidth consumed.

Since more bandwidth means a more expensive as well as complex system, interlaced video reduces the signal bandwidth by a factor or two for a given line count then refresh the rate. As TV sets designed with an interlaced program scanning method are less expensive, consequently, it makes TV models such as these more popular than competing models requiring progressive program scanning method.

On the other hand, these types of TV models display images less desirable as the images interlaced devices projects are prone to distracting image artefacts. This also causes intentional blurring, flickering (also referred to as “interline twitter” and is produced by the image on the display screen that contains vertical detail and approaches the horizontal resolution of the video format).

All of these that are present in an interlaced program scanning method have been totally eliminated with the progressive program scanning method. Thus, a more vivid or rich image is displayed with this image projection method.

When selecting the most appropriate display device for your home theater, you need to consider the over-all quality that your device will provide. Choose for quality even though it would be pricey than the lesser quality image display projecting TV designs. Consider the imminent consequence that such decision will create.



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Posted on September 1, 2013 by 0 Comments Short URL


Alphonso Soosay, an accomplished musician and sound recording specialist has been in the industry for more than 30 years. In this blog Alphonso shares all his experiences and knowledge in the recording and home theatre industry. Alphonso Soosay's Blog

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