The Difference Between Progressive Scan and Interlaced HDTV

When we look at specifications for most HDTV televisions we are bound to find resolutions to be written in the format 1080i. This basically means that this resolution supports 1920 pixels width wise and 1080 pixels height wise in interlaced at 60 frames per second. When a specification for and HDTV states a primary standard of 1920 x 1080 with a frame rate of 30 p means 1920 pixel wide with 1080 pixels height at 30 frames per second progressive scan. The small letter that sits behind the number when looking at supported resolutions is what tells us if the supported resolution is progressive scan or interlaced.

Images in interlaced formats are constructed in two parses the first one fill odd rows while the other ones will even rows.  While interlacing was very noticeable a few years ago, HDTV televisions displaying 1080i resolutions achieve sharp images due to the fact that refresh rates are very fast compared to analog televisions. With analog Tvs, broadcasters had to be very careful with what they transmitted since the limitations of this technology could easily show their ugly face. Even with the fast refresh rated found on modern HDTVs, interlaced signals have a tendency to lose detail in the edges of images especially in lower resolutions with lower a lower frames per second count. This effect is very noticeable during fast moving scenes. Artifacts introduced under these circumstances are usually blurring of the image and very noticeable distortion around the edges.

Progressive scan television formats display images in only one parse. Much like how text flows on a page. It is the scanning method that has been used on computers for decades. Movement is usually from top to bottom filling every row in one run. To visualize better how this scanning technology works, you can imagine someone typing very fast on a computer. You would see text appearing from left to right and from top to bottom. That is how this scanning technology works. It also more resource demanding to television broadcasters and television sets alike requiring almost double the bandwidth necessary but the results are pretty much astonishing. There are basically no black pixel rows as opposed to interlaced where the black pixel rows take possible color pixels away from the whole picture. This makes the whole image more solid and more detailed than interlaced formats.

In conclusion, progressive scan offer the best possible image quality and the best possible experience provided that the broadcast supports progressive scan. This format has become a favorite with DTV users of both HDTVs and SDTVs for its solid image and better brighter overall image.

Here is a nice image to help you get an idea of how these scanning technologies look. A picture is worth a thousand words.

Image by: Grayshi used under the Creative Commons Attribution ShareAlike 3.0