Progressive Scan - What You Need to Know

Sony DVP-SR210P Progressive Scan DVD Player
Sony DVP-SR210P Progressive Scan DVD Player. Image provided by Sony Electronics

DVD and Home Theater

DVD was the core of the home theater revolution that began with its introduction in the mid-1990's. With its outstanding image quality (over VHS and other analog TV), DVD was a huge advance in home entertainment. One of the main contributions of DVD was the employment of the progressive scan option for television viewing. Progressive scan pushes the limits of standard resolution and provides a more film-like image display that is more pleasing for viewing DVDs on a television or video display.

The following is an overview of progressive scan and how it contributes to the home theater experience.

Interlaced Scan - The Foundation Of Traditional Video Display

Before we get into the nature of progressive scan, it is important to understand the way traditional television images were once displayed on a TV screen. Analog television signals, such as those from a local TV station, cable company, or VCR were displayed on a TV screen using a technology known as Interlaced Scan. Basically, there were two dominant interlaced scan systems in use: NTSC and PAL.

NTSC is based on a 525-line, 60 fields/30 frames-per-second at 60Hz system for transmission and display of video images. This is an interlaced system in which each frame is scanned in two fields of 262 lines, which is then combined to display a frame of video with 525 scan lines. Countries with an NTSC foundation are he U.S., Canada, Mexico, some parts of Central and South America, Japan, Taiwan, and Korea.

PAL was/is the dominant format in the World for analog television broadcasting and video display (sorry U.S.) and 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. Several distinguishing features are one: A better overall picture than NTSC because of the increased amount of scan lines.

Two: Since color was part of the standard from the beginning, color consistency between stations and TVs are much better. In addition, PAL has a frame rate closer to that of film. PAL has a 25 frames per second rate, while film has 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.

The remainder of this article discusses the issue of progressive scan as it relates to the NTSC video system, which has special considerations with regards to the progressive scan issue.

The Development Progressive Scan

With the advent of home and office desktop computers, it was discovered that using a traditional television for the display of computer images did not yield good results, especially with text. This was due to the effect of interlaced scan. In order to produce a more pleasing and precise way of displaying images on a computer, progressive scan 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, as is done with interlaced scan.

In other words, in progressive scan, the 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 (lines or rows 1,3,5, etc... followed by lines or rows 2,4,6). By progressively scanning the image onto a screen every 60th of a second rather than "interlacing" alternate lines every 30th of a second, a smoother, more detailed, image can be produced on the screen that is perfectly suited for viewing fine details, such as text, and is also less susceptible to interlace flicker.

Progressive Scan Applications

Seeing this technology as way to improve the way we view images on a video screen, progressive scan was applied to the display of DVD on TVs.

Progressive Scan vs Line Doubling

With the advent of large screen, HD, and flat panel televisions like (Plasma, LCD), and video projectors, the resolution produced by traditional television, VCR, and DVD sources are not reproduced very well by the interlaced scanning method.

To compensate for this problem, television makers began to introduce the concept of Line Doubling. Although there are many ways this can be applied, at its core, a TV with line doubling capability 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 the television screen. The drawback with these systems, however, is that motion artifacts can result, as the newly created lines also have to move with ​the action of the image. Video processors are employed to address this issue, but results vary depending on the actual technology used.

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 one other factor that prevents the accurate display of movies originally shot on film to be viewed properly on a TV. The problem: Films are shot at 24 frames per second and NTSC video is produced at 30 frames per second.

When a film is transferred to DVD (or video tape), the differing frame rates of film and video must be addressed. If you have ever tried to transfer an 8 or 16MM home movie by videotaping the movie screen as the movie is being shown, you will understand 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 video tape back. The reason for this is that the frames on the screen are moving at ​a slower rate than the video frames in the camera, and since the frame movement does not match up, this produces the severe flicker effect when the film is transferred to video without any adjustment.

In order to eliminate this flicker effect, when a film is transferred to video (whether DVD, VHS, or other format), the film frame rate is "stretched" by a formula that more closely matches the film frame rate to the video frame rate. For a graphic representation of this formula, check out the following chart by Projector People.

Progressive Scan and 3:2 Pulldown

In the preceding paragraph I outlined the manner in which film is transferred to video, however, since this process is accomplished within the interlaced video environment, the question remains as to how to display this accurately on a TV.

This is where a progressive scan DVD player with 3:2 pulldown detection becomes important. In order to see a film in its most correct state, it should be shown at 24 frames per second on either a projection or TV screen. So, in order to do this as accurately as possible, the DVD player needs to be able to 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, while still being compatible with a 30 frames per second video display system (NTSC). This is accomplished by a DVD player that is equipped with an special type of MPEG decoder, combined with what is referred to as a De-interlacer that reads the 3:2 pulldown interlaced video signal off the DVD and extracts the proper film frames from the video frames, progressively scans those frames, makes any artifact corrections, and then transfers this new video signal through a special connection on the DVD player. This connection is known as a Progressive Scan Component Video connection, which is most commonly labeled as Y, Pb, Pr.

The Two Types Of Progressive Scan

One thing to keep in mind, is there are two types of progressive scan, which is also referred to as 480p. When in reference to DVD players this can apply to progressive scan or progressive scan with 3:2 pulldown detection. If your DVD player has progressive scan without 3:2 pulldown detection, it will still produce a smoother image than traditional interlaced video, as the progressive scan DVD 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. However, if the DVD player has the addition of 3:2 pulldown detection, not only will your video display a smoother progressively scanned image, but you will experience the DVD film in as close a state as possible to what you would see coming from an actual film projector, except that it is still in the video domain.

Progressive Scan and HDTV

In addition to DVD, progressive scan is applied to DTV and HDTV 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 or an external HD tuner, HD Cable, or Satellite box.

What You Need To Access Progressive Scan

In order to access progressive scan, both the source component, such as a DVD player, HD cable, or satellite box, and the TV, video display, or video projector need to be progressive scan capable (which all are if purchased 2009 or later), component video output or other type of connection on the source device (DVD/Blu-ray Disc player, Cable/Satellite Box), such as DVI (Digital Video Interface) or HDMI (High Definition Multi-media Interface) that allows the transfer of standard and high-definition progressive scan images to a similarly equipped television.

On DVD players, the progressive scan signal is sent via component video connections, which are labeled Y, Pb, Pr, or via HDMI or DVI connections. Component video connections labeled Y,Cb,Cr transfer only interlaced signals. In addition, standard AV and S-Video connections do not 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.

In addition, in order to view progressive scan with reverse 3:2 pulldown, either the DVD player or TV needs to have 3:2 pulldown detection (not a problem for anything purchased 2009 or later). The preference would be for the DVD player have the 3:2 pulldown detection and actually perform the reverse pulldown function, with a progressive scan capable television displaying the image as fed from the DVD player. There are menu options in both a progressive scan DVD player and a progressive scan capable (HDTV) television that will assist you setting up a progressive scan capable DVD player and television or video projector.

Progressive Scan and Beyond

Progressive Scan is one of the technical foundations of improving the TV and home theater viewing experience. Since it was first implemented, things have evolved, DVD now coexists with Blu-ray, and HDTV is transitioning to 4K Ultra HD TV, and with that progressive scan has not only become a part of how images are displayed on a screen, but also provided an additional foundation for further video processing techniques, such as video upscaling. In other words, if it wasn't for DVD and Progressive Scan, those big screen TVs wouldn't look so good.

Original Publish Date: 08/22/2004 - Robert Silva

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