Interlaced Scanning

In Interlaced scanning alternating sets of lines are displayed. First even numbered lines are displayed and then odd numbered lines are displayed. Each even set of lines are displayed for 1/60th of a second and then the odd lines are displayed for 1/60th of a second in case of 60 Hz refresh rate. Because each field happens so quickly we are given the illusion of a whole image.

Because you’re only capturing half of the image at a time, movement within the frame (due to either camera movement or subject movement) may cause motion artifacts. This happens especially when the movement is quick enough to cause noticeably different positions of the fields.

Video sources that are listed with the letter i are called interlaced. An example of this would be 480i. Interlaced video displays even and odd scan lines as separate fields. The even scan lines are drawn on the screen, then the odd scan lines are drawn on the screen. Two of these even and odd scan line fields make up one video frame.

Progressive Scanning

Progressive scanning captures entire image per frame. It results in a clearer image and handles movement differently. It does not have artifacts which are present in interlaced scanning.

Progressive video is more expensive but desired. The scanning technique results in the clearest images without worrying about too many artifacts. It also allows for better viewing of fast motion video like in action sequences in movies and sports.

Video sources that are listed with the letter p are called progressive scan signals. Examples of this would be 480p. Progressive scan video content displays both the even and odd scan lines on the screen at the same time.

Interlaced vs Progressive Scanning
Interlaced vs Progressive Scanning

Summary

The recording, playback and transmission of video used either progressive or interlaced techniques. Interlaced has its roots in the broadcasting industry and is still widely used because of its efficiency and reliability. Progressive is ideal for higher quality displays for smoother video output.