What is Progressive Scan Video?

How progressive scan improves standard and hi-def video quality

Effective video processing is one of the keys to displaying the best TV and projected images. Progressive Scan is a processing technique that paved the way and is still in use as the foundation of "modern" video processing techniques.

Interlaced Scan vs Progressive Scan
Interlaced Scan vs Progressive Scan. Images provided by Samsung

What Interlaced Scan Is

Before we get into what progressive scan is we need to understand Interlaced Scan. Analog TV broadcasts (before the DTV transition), cable/satellite, DVD (before HDMI) or VCR are displayed on a TV screen using a technology known as interlaced scan. There were two main interlaced scan systems in use: NTSC and PAL.

  • NTSC is based on a system of 525-lines, 60 fields/30 frames-per-second at 60Hz for transmission and display of video images. Each frame is split into two fields of 262 lines. The lines are sent alternately and then displayed as an interlaced image. Countries with an NTSC foundation are the U.S., Canada, Mexico, some parts of Central and South America, Japan, Taiwan, and Korea.
  • PAL is based on a 625 line, 50 field/25 frames a second, 50HZ system. The signal is interlaced, like NTSC, into two fields, composed of 312 lines each. In addition, PAL has a frame rate closer to that of film. PAL has a frame rate of 25 per second, while film content is based on a frame rate of 24 frames per second. Countries that have a PAL system foundation include the U.K., Germany, Spain, Portugal, Italy, China, India, most of Africa and the Middle East.

What Progressive Scan Is

With the advent of desktop computers, it was discovered using a traditional TV for the display of computer images didn't yield good results, especially with text. This was due to the effect of interlaced scan. In order to produce a more precise way of displaying images on a computer monitor, progressive scan technology was developed.

Progressive scan differs from interlaced scan in that the image is displayed on a screen by scanning each line (or row of pixels) in a sequential order rather than an alternate order. This means in progressive scan, image lines (or pixel rows) are scanned in numerical order (1,2,3) down the screen from top to bottom, instead of in an alternate order (1,3,5, etc... followed by lines or rows 2,4,6).

By progressively scanning the image onto a screen in one sweep rather than building the image by combining two halves, a smoother, more detailed image can be displayed that is better suited for viewing fine details, such as text and motion and is also less susceptible to flicker.

Seeing improvement in computer video displays, progressive scan technology was next applied to TV and DVD.

Line Doubling

With the advent of high definition Plasma, LCD TVs, and video projectors, the resolution produced by traditional TV, VCR, and DVD sources were not reproduced very well by the interlaced scanning method.

To compensate, in addition to progressive scan, TV makers also introduced the concept of Line Doubling.

A TV with line doubling creates "lines between lines", which combine characteristics of the line above with the line below in order to give the appearance of a higher resolution image. These new lines are then added to the original line structure and all the lines are then progressively scanned on a TV screen.

The drawback of line doubling is that motion artifacts can result, as the newly created lines also have to move with the action in the image. To smooth out the images, additional video processing was usually employed.

3:2 Pulldown – Transferring Film to Video

Although progressive scan and line doubling attempt to address the display flaws of interlaced video images, there is still another problem that prevents the accurate display of movies originally shot on film to be viewed properly on a TV – video frame rate.

For PAL-based source devices and TVs, this is not a big issue as the PAL frame rate (25 fps) and film frame rate (24 fps) are very close, so minimal correction is needed for showing film accurately on a PAL TV screen. However, that is not the case with NTSC as it produces and displays video at 30 frames per second.

This means when a film is transferred to DVD (or videotape) in an NTSC-based system, the differing frame rates of film and video must be reconciled.

If you have tried to transfer an 8 or 16mm home film movie by videotaping the movie screen using a camcorder as it's being shown, you will see this issue.

Since the movie frames are projected at 24 frames per second, and the camcorder is taping at 30 frames per second, the film images will show a severe flicker effect when you play your videotape back. The reason is the frames on the screen are moving at a slower rate than the video frames in the camera. Since the frame movement does not match up, this produces noticeable flicker when the film is transferred to video without any adjustment.

To eliminate flicker, when a film is transferred professionally to video (whether DVD, VHS, or another format), the film frame rate is "stretched" by a formula that more closely matches the film frame rate to the video frame rate.

Progressive Scan and 3:2 Pulldown

In order to see a film in its most correct state, it should be displayed at 24 frames per second using a projector or TV that can display that frame rate natively.

To do this accurately in an NTSC-based system, the source, such as a DVD player needs to have 3:2 pulldown detection, reverse the 3:2 pulldown process that was used to put the video onto DVD, and output it in its original 24 frames per second format and in progressive scan (aka 24p).

OPPO UDP-203 24P DVD Setting

This is accomplished by a DVD (Blu-ray/Ultra HD Blu-ray) player equipped with a special type of MPEG decoder, combined with a deinterlacer that reads the 3:2 pulldown interlaced video signal off of the DVD and extracts the proper film frames from the video frames. The frames are then progressively scanned, artifact corrections are made, and the new video signal is sent out through a progressive scan-enabled component video or HDMI connection to a compatible TV or video projector.

If your DVD player has progressive scan without 3:2 pulldown detection, it will still send a smoother image than interlaced video. The player will read the interlaced image of the DVD and process a progressive image of the signal and pass that on to a TV or video projector within a 30 fps system.

Check your DVD, Blu-ray, or Ultra HD Blu-ray player for the 24p feature – Also check your TV specs to see if it is 24p compatible.

Progressive Scan and HDTV

In addition to DVD, progressive scan is applied to DTV, HDTV, Blu-ray Disc, and TV broadcasting as well.

Standard definition DTV is broadcast in 480p (the same characteristics as progressive scan DVD – 480 lines or pixel rows progressively scanned) and HDTV is broadcast at either 720p (720p lines or pixel rows progressively scanned) or 1080i (1,080 lines or pixel rows that are alternately scanned fields made up of 540 lines each). In order to receive these signals, you need an HDTV with either a built-in HDTV tuner, an external HD tuner, HD Cable or Satellite box.

What You Need To Access Progressive Scan

To access progressive scan, both the source component, such as a DVD player, HD cable, satellite box, antenna and the TV or video projector need to be progressive scan capable (which most are since the mid-2,000's). The source also needs to have a progressive scan-enabled component video output, or a DVI or HDMI output that allows the transfer of standard and high-definition progressive scan images to a similarly equipped TV or video projector.

Composite and S-Video connections don't transfer progressive scan video images. If you hook up a progressive scan output to a non-progressive scan TV input, you will not get an image (this applies to most CRT TVs – all LCD, Plasma, and OLED TVs are progressive scan compatible).

Video is placed on a DVD in an interlaced form, progressive scan is applied by the DVD player as one of its playback options.

NeuNeo 2805 DVD Player – Progressive Scan Setting