Progressive Scan – The basis of video processing
With its introduction in the mid-1990s, DVD became the core of the home theater revolution. With its significantly improved picture quality over VHS and analog TV, DVD has marked a major advance in home entertainment. One of the major contributions of DVD was the employment of the progressive scanning technique to improve the quality of television.
Interlaced Scan – Establishing Traditional Video Screen
Before we find out what progressive scanning is and how important it is to enhance the TV viewing experience, it is important to understand how traditional analog video images are displayed on a TV screen. Analog TV signals , such as those from a local station, cable company 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 60 Hz for the transmission and display of video images. It is an interlaced system in which each frame is scanned in two fields of 262 lines, which are then combined to display a frame of video with 525 scan lines. Countries with an NTSC foundation are the USA, Canada, Mexico, some parts of Central and South America, Japan, Taiwan and Korea.
- PAL is based on a 625-line, 50-field / 25 frames per second, 50HZ system. The signal is, like NTSC, in two fields, composed of 312 lines each. In addition, PAL has a ram rate closer to that of the film. PAL has a frame rate of 25 frames per second, while movie content is based on a frame rate of 24 frames per second. Countries that have a PAL foundation include the United Kingdom, Germany, Spain, Portugal, Italy, China, India, most of Africa and the Middle East.
What Progressive Scan Is
With the advent of home and office browser computers, it was discovered that the use of a traditional TV for displaying computer images did not yield good results, especially with text. This was due to the effect of interlaced scan technology. To provide a more enjoyable and accurate way to display images on a computer, progressive scanning technology has been developed.
Progressive scanning differs from an 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) from top to bottom in the screen, instead of in an alternate order (lines or rows 1,3,5 , etc … followed by lines or rows 2,4,6).
By scanning the image on a screen on one screen rather than building the image by combining two halves, a smoother and more detailed image can be displayed that is better suited to viewing fine details, such as text and motion also less susceptible to interlace flashing.
If we see this technology as a way to view the way we view images on a video screen, then the progressive scanning technology is applied to DVD.
With the advent of large screen high definition Plasma , LCD TVs and video projectors , the resolution produced by traditional TV, video and DVD sources is not very well reproduced by the interlaced scanning method.
To compensate, in addition to the progressive scan, TV makers also introduced the Line Doubling concept.
Although there are many ways it can be applied, a TV with line doubling may create ‘lines between lines’, combining the properties of the line above with the line below 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.
However, the disadvantage of line doubling is that moving artifacts can occur, as the newly created lines must also move with the action in the image. To make the images smooth, additional video processing is usually required.
3: 2 Pulldown – Transfer from movie to video
Although progressive scanning and line doubling attempt to address the display errors of interlaced video images, there is another problem that prevents the correct display of films originally shot on film, viewed correctly on a TV. For PAL-based source devices and TVs, this is not a big issue as the PAL frame rate and movie frame rate are very close. It is therefore a minimal correction to display the movie accurately on a PAL TV screen. However, this is not the case with NTSC.
The problem with NTSC is that movies are generally shot at 24 frames per second and NTSC video is produced and displayed at 30 frames per second.
This means that when transferring a movie to DVD (or videotape) in an NTSC system, the different frame rates of movie and video must be addressed. If you have ever tried to transfer an 8mm or 16mm home or movie by filming the movie screen as the movie is shown, you will understand this issue. As the film frames are projected at 24 frames per second and the camcorder attaches at 30 frames per second, the film images will show a serious flickering effect when you play back your videotape. The reason for this is that the frames on the screen move at a slower pace than the video frames in the camera, and since the frame motion does not match, it causes the severe flickering effect when the film is transferred to video without any adjustment.
To prevent flicker, a movie that is professionally transferred to video (DVD, VHS, or other format) is “stretched” with a formula that matches the movie frame rate to the video frame rate.
However, the question remains how to display it accurately on a TV.
Progressive scan and roll 3: 2
To see a movie in its most correct state, it must be displayed on a projection or TV screen at 24 frames per second.
In order to do this as accurately as possible in an NTSC-based system, the source, like a DVD player, must detect 3: 2 detection, reverse the 3: 2 fold-out process used to convert the video to DVD place, and output it in its original 24 frames per second format, while still being compatible with a 30 frames per second video display system.
This is achieved by a DVD player equipped with a special type of MPEG decoder, combined with what is referred to as a deinterlacer that reads the 3: 2 expandable video signal from the DVD and the correct film frames from the video frames withdraw. , scan the frames gradually, make any artifact corrections, and then transfer this new video type through a progressive scanner-based component video (Y, Pb, Pr) or HDMI connection .
If your DVD player has progressive scan without 3: 2 scrolling, 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 a progressive image of the signal processing leading to a TV or video projector.
However, if the DVD player detects 3: 2 performance, your video will not only display a smoother scanned image, but you will experience the DVD movie as close as possible to what you would see coming from an actual movie projector, except that it’s still in the video domain.
Progressive Scan and HDTV
In addition to DVD, progressive scanning is also applied to DTV, HDTV , Blu-ray Disc and TV broadcasting.
For example, standard definition DTV is broadcast in 480p (the same features as progressive scan DVD-480 lines or scanned pixel sequences) and HDTV is broadcast in 720p (720p scanned lines or pixel sequences) or 1080i (1,080 lines or pixels rows that alternately scanned fields consist of 540 lines each) . To receive these signals, you need an HDTV with a built-in HDTV receiver or an external HD receiver, HD cable or Satellite box.
What you need to get progressive scan
To access progressive scan, both the source component, such as a DVD player, HD cable or satellite box, and the TV, video monitor or video projector, progressive scan (all purchased in 2009 or later), and the source device (DVD / Blu-ray Disc player, Cable / Satellite box) must have a progressive scanable component video output, or a DVI (Digital Video Interface) or HDMI (High Definition Multi-Media Interface) output that allowing the transfer of standard and high definition progressive scan images to a similarly equipped television.
It is important to note that standard composite and S-Video connections do not transmit progressive scan video images. Also, if you turn on progressive scan output to a non-progressive scan TV input, you will not get a picture (this actually only applies to most CRT TVs – all LCD, Plasma and OLED TVs are progressive scan-compatible).
To see progressive scan with inverted 3: 2 unrolling version, the DVD player or TV should detect 3: 2 detection (not a problem with anything purchased in 2009 or later). The preference will be for the DVD player that has the 3: 2 roll-down detection and the reverse roll-out function works. With a progressive scanable television, the picture can be fed from the DVD player. There are menu options in both a progressive scan DVD player and an HDTV TV that can help you set up a DVD player and television or video projector in a progressive scan.
The bottom line
Progressive Scan is one of the technical foundations of improving the TV and home viewing experience. Since it was first implemented, things have evolved. DVD now coexists with Blu-ray , and HDTV has been switched to 4K Ultra HD TV , and with that progressive scan it has not only become part of how images are displayed on a screen, but also an additional basis for further video processing techniques, such as video scaling .