With the advent of large screen, HD, and flat panel televisions, 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 is applied, basically, a television 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 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 an NTSC television. The problem: Films are shot at 24 frames per second and NTSC video is produced at 30 frames per second. This means that, unlike PAL, there are special problems that have to be addressed with transferring film to video in the NTSC standard.
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. Basically, 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 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 an 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 NTSC interlaced video environment, the question remains as to how to display this accurately on a television. This is where a progressive scan DVD player with 3:2 pulldown detection becomes important. Basically, in order to see a film in its most correct state, it should be shown a 24 frames per second on either a projection screen or a television 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 ( such as the Faroudja DCDi ) 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 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 referenced to DVD players: progressive scan and 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 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.
Continue On To Page 3: Progressive Scan - Additional Applications and What You Need
