Resolution and Quality Breakdown

Interlaced and Progressive Scanning

Designed in the 1930s, to provide the best possible image on a CRT (cathode ray tube) while conserving bandwidth, interlaced scanning works by painting the odd lines of an image, followed by the even lines, all within 1/25 or 1/30 of a second. You do see an acceptable picture, but you also get flickering and artifacts.

Many in the industry are now touting progressive scanning. Progressive scanning is better than interlaced, because it writes a full frame of video across the screen every 1/50 or 1/60 of a second. Instead of getting an image split in half, you get the entire picture drawn at one time. As opposed to interlaced scanning, progressive scanning gives you fewer artifacts and flickering.

The problem is, progressive scan devices, like DVD players, only work with digital high-definition TVs. This means manufacturers still need to deal with the problems associated with interlaced scanning. We are a long way away from having digital HDTVs in every home.

Problems Caused by Interlaced Scanning

Feathering or "jaggies"

Artifacts such as feathering ("jaggies) often occur where there is motion in an image, for example when an image moves from left to right. Because the fields are interlaced, jagged vertical edges appear.

"Combing" or "saw tooth"

Artifacts such as combing, saw teeth, and serrations occur when subtitles are out of synch with film frames. With images, they often occur when there is motion in an image, similar to the feathering cited above.

 
Aliasing and "jaggies"

Artifacts such as jaggies often occur in interlaced versus progressive images.

 
Reduced quality, brightness, definition

Interlaced scanning causes a number of problems. You are often able to see the scan line structure, and saw-tooth type artifacts along the edges of objects. These effects further reduce the quality, brightness, and definition of the object and text you are viewing.

Credits
* Images provided courtesy of Secrets of Home Theater and High Fidelity and Brian Florian. Please refer to Brian's informative article, "An Explanation of Film-to-Video Frame Rate Conversion for NTSC."

** Images provided courtesy of David Perry and Stuart Wright. Please refer to David and Stuart's informative article on the "Disadvantages of interlaced scanning."

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