video & live streaming

Difference Between Interlaced And Progressive Video

Interlaced and progressive video, often known as the methods of ‘painting’ an image on a screen, are the major ways of video images production.

Difference between Interlaced and progressive video
Interlaced Vs Progressive Scan Video

What is Interlaced Scan Video?

Video sources with the letter ‘i’ are called interlaced (480i or 1080i for example). Also known as Interlaced scan, it is a method for doubling the frame rate of a video display without taking up additional bandwidth.
The interlaced video demonstrates even and odd scan lines as two individual fields. At first, the even scan lines pass on the screen and then the odd scan lines pass. Two of such even and odd scan line fields make one video frame. This means it utilizes two video fields to create one frame. One field has the odd lines whereas the other contains all the even lines of the image(60 fields are scanned per second- 30 odd and 30 even). It was designed primarily to minimize the bandwidth requirements for video signal transmission.

Interlaced is very significant in broadcasting. Interlacing has been used for a long time in analog television broadcasts based on the NTSC (U.S.) and PAL (Europe) formats. Interlaced videos are great for broadcasting as video images can be processed onto the screen with very little bandwidth. Interlacing offers full vertical detail with the same bandwidth as that of a full progressive scan, but with twice the frame rate and refresh rate. (60i is 60 interlaced images per second). The interlaced video basically produces a better quality video.

The drawback of interlaced video is that in fast motion, it may be blurred as only half of the image is captured at a time, movement along the frame causes motion artifacts. Particularly when the movement is rapid, causing different positions of the fields. For instance, from a moving car, we can notice motion artifacts if filmed by interlaced. Nowadays, higher power graphics cards have good quality deinterlacing as a built-in feature.

What is Progressive Scan Video?

Video sources with the letter p are called progressive scan signals. Examples of this would be 480p, 720p. Also referred to as non-interlaced scanning, it is a process of displaying, storing or transmitting videos where all the lines of every frame are given in sequence. Largely used in CRTs, HDTV displays and computer monitors, it demonstrates a detailed image on the screen and is clutter-free. This is why it has higher bandwidth requirements, which was initially a limitation, but not anymore.

Here, video signals are generated using horizontal lines. An interlaced picture draws every other line and alternates between drawing odd lines and even lines, whereas, a progressive scan picture draws every line in sequence. Hence, a progressive scan video signal sends twice as much data than an interlaced signal. Progressive scan video content shows the even and odd scan lines, that is the entire video frame on the screen at the same time. Here, the lines are drawn or ‘painted’ one at a time in sequence. A single frame image is drawn every 1/60th of a second, so twice the detail is sent in the same period of time as of interlaced systems.

To use progressive video, it is essential that both the display and the source are compatible with progressive scan.

Major Differences between Interlaced vs Progressive Scan Video

Comparison Unit Interlaced Scan Progressive Scan
Basic Scanning through dividing a single frame. The whole frame is scanned at once.
Efficiency Low High
Quality Degraded Better
Combing effect Present Absent
Speed of display One field in 1/60th seconds One image in 1/60th seconds

Interlaced or Progressive: Which one is Better?

Let’s discuss two instances- two films, one recorded progressively and one recorded interlaced. Now, if the progressive one is played by a traditional broadcasting system which uses interlaced encoding, the system will play them reasonably well. It will not be even noticed that the image is interlaced. But when the interlaced video is played on a screen that uses progressive scanning, problems will arise. Since half the data was not there, the system tries creating progressive images from half ‘stills’ resulting in the missing lines becoming visible. It is evident from here that progressive scan is better than interlaced scan since:

  • It provides a more vivid and realistic display, which is appealing.
  • With the emergence of modern displays such as LCDs and LEDs, this display technology is permanent.
  • Though interlaced scanning is being used in the broadcasting industry till now, continuous technological advancements and falling prices of the associated electronic devices indicate that systems based on progressive scanning will most certainly dethrone those based on interlaced scanning in the near future.

The terms, interlaced and progressive video is the raster scan techniques. The progressive scan is newer technology and interlaced scan is older but widely used. Moreover, making and scanning of progressive scan video is costlier in comparing to interlaced scan however its images and videos qualities are clearer.