# Analysis of 720 p 1080i and 1080 p

Source: Internet
Author: User
With the increasing number of HDTV programs downloaded from the internet, the introduction of kmplayer software, the increase of powerdvd and windv HD playback functions, and the acceptance of HDTV players, HDTV and us are getting closer and closer. Many people begin to understand HDTV.

When talking about HDTV, many people think it is very simple, not 720 p or I, but a maximum of P. However, many people do not know that there is no 1080i or 1080p difference between Flat TVs. Few people know that P is only the standard used by several American television stations. Many of the concepts about HD are based on the idea that even 720 p, I, and P are incorrect. Let's trace the source together, start with the concepts of 720 p, I, and P, correct some misunderstandings in high definition, and understand the true face of HD.

Starting from line-by-line scanning

The I in 720 p and I is interlace, which indicates that the line-by-line scan is progressive and that the line-by-line scan is performed. To clarify these two terms, we need to start with a simulated crt TV. The traditional crt TV works in a way that uses an electron beam to scan the screen and then emit light to display the image. During the transmission of TV signals, due to bandwidth restrictions, it is only possible to transmit the line signal to save bandwidth. Taking ntsc TV as an example, a 525-row image is divided into two sets during work. The first is called an odd number, scan only odd rows (1, 3, 5... Rows), while the second field (even fields) only scans even rows (scanning 2, 4, 6 in sequence... Rows). The number of rows scanned by the original frame of the image is completed through two scans. Because the human eye has a temporary effect on vision, it is still a complete image in the eye, which is an interlace scan. The NTSC program has a total of 525 lines of scanning lines, 60 images per second, expressed as 60i or 525i. If it is a row-by-row scan, it is called 60p or 525 p. The pals program contains 625 rows, 50 images per second, which are 50 I or 625 I, and 50 p or P. Remember, this is for CRT TVs.

The above representation not only represents the scanning format of the crt TV, but also the format of the image taken by the camera. Because the television system was originally a line-by-line scanning system, all the cameras corresponding to NTSC and palth TV programs were scanned by line-by-line scanning, that is, all the NTSC/palth programs taken by TV cameras, all are the interlace scanning signals, expressed as 525/60 I and 625/50 I respectively. Remember, this is for a TV camera.

For a simulated TV image, the image is represented by a scanned line, and the palth is 625/50 I; NTSC is represented by 525/60 I. For digital signals, the resolution is expressed in pixels or resolutions. For example, for a paly program, the resolution is 720*576, which can be expressed as 576 P on a row-by-row basis and the behavior is 576i. The NTSC resolution is 720*480, 480 p per behavior, and I per behavior. Remember, this is for TV images.

As mentioned above, some of them are like tongue twisters, but they are also a must for figuring out the concepts of 720 p, I, and P. You should remember that for HD, the concepts of 720 p, I, and P must be known from the television, the camera, and the image format. The TV, the camera, and the image format are different and associated different concepts.

Different definitions of HD
HDTV, also known as HDTV, is defined by CCIR International Radio Advisory Committee. The ratio of HDTV images is 16: 9. When viewers are watching at three times the screen height, the images should be transparent, it is basically close to a real object.

According to the definition of ITU, HDTV has two times the definition of conventional TV in the horizontal and vertical directions, and the image aspect ratio is 16: 9. The subjective image quality is equivalent to the standard of the HDTV studio for interlace scanning.

Image Format: in addition to some American TV stations, 1280*720 is the HDTV standard. In addition to the standard, many countries around the world, including China, Europe, Australia, Japan, and South Korea, the new generation of HD CDs, HD DVDs, and BD, resolution standards are 1920*1080. No country has adopted the 1280*720 standard. However, this still does not show how the concepts of 720 p, I, and P come from. Please do not worry about it. When we talk about HD, we immediately think of LCD, plasma, and other flat-panel TVs. The definition standard was first formulated and traced back to the 1980s S, the us hd standard was determined to have been in the 1990s s and has been in use for more than 20 years. At that time, flat TVs were not available, and the standard was determined by CRT TVs, therefore, the 720 p, I, and P concepts have a strong CRT flavor.

In terms of television sets, considering the technical limitations of CRT TVs at that time, and to take care of computer industry displays as a line-by-line scanning system, when CRT Displays 1280*720 of images, A row-by-row scanning system (720 p for short) is used. While in the display of 1920*1080 images, the use of the barrier system, referred to as 1080i. According to the technology at that time, it was not possible to produce a 10 80 p crt TV. A 10 80 p crt TV was only available in the 21st century. This is the concept of 720 p, I, and P.

However, the CRT has been eliminated and the flat panel TV has been replaced. LCD and plasma TVs are fixed pixel display devices that do not need to be scanned when displaying images. In addition, each pixel can be considered as emitting at the same time, if it is necessary to associate with the concept of line-by-line separation, it can be considered that liquid crystal and most plasma TVs are scanned on line-by-line. So can 720 p, I, and P be canceled? The answer is no, because there is another camera format.

From the perspective of the camera, although the HD camera is digital, the scanning method is used from the simulated camera. The traditional simulated camera is completely split, while the HD camera, the row-by-row scan format is also added while the format of the row-by-row scan is retained.

The HD camera not only keeps the distinction between Row-by-row and row-by-row, but also keeps the difference between the 50Hz frequency of palms and the 60Hz frequency of NTSC. Although there is no difference between the PAL and NTSC in HD, however, in traditional NTSC regions such as the United States, Japan, and South Korea, the 60Hz frequency system is retained, while in China, Australia, and Europe, the 50Hz system is retained. HD programs are all digital signals, so they only need to be expressed in resolution. During the shooting, HDTV is divided into two forms: line-by-line scanning and frame rate (number of lines-by-line images displayed per second) or field frequency (the line-by-line images displayed per second) they are also different.

1280*720 has five frame frequencies: 60 p, 50 p, 30 p, 25 p, and 24 P, which can be referred to as 720 p, it can also be expressed as 720/60 p (used by abc TV), 720/50 p, 720/30 p, 720/24 p (Fox), and 720/25 p respectively. Among them, 720/50 p and 720/25 P did not exist. Later, when Germany selected the HD image standard, it intentionally chose the P system. Considering that Germany is traditionally a 50Hz system country, as a result, some manufacturers have launched video cameras that support 720/50 p and 720/25 P, but no country has chosen such a standard. At most it is a topic.

The case of 1920*1080 is more complicated. The expression of the line-by-line is 1080i, and that of the line-by-line is 1080 p. In the United States, Japan, the field frequency is 60Hz, can be expressed as 1080/60 I, in China, Europe, Australia, is 1080/50 I, these two formats can be called 1080i. This is not the end of things. In order to facilitate the production and exchange of high-definition programs, the 1080/24 P standard is adopted globally, which is also used as the standard for digital movie cameras, the famous movie before Dipper was shot with a 1080/24 P camera. Many hd TV series, such as otaku, are also 1080/24 P (1080 p for short.

However, this is still not the full meaning of P. For flat TVs, we can actually think that there is no difference between I and P, because at present, the image processing circuit technology is developing very fast and the computing speed is very fast, the processing capability is very strong, and all of them have line-of-line technology. The so-called multiline technology is to convert the 1080i image of the barrier into a row-by-row 1080p image. It can perfectly process 1080/50 I to 1080/50 p, and 1080/60 I to 1080/60 p, programs that include 1080/24 P can be processed very easily as 1080/50 P or 1080/60 p. In addition, any flat-panel TV has such a circuit, and a slightly upscale flat-panel TV has a good processing effect.

More HD flat disputes

At this point, it seems that there is no TV format. The TV format is more complex. The resolution of liquid crystal and plasma TV is different, and the resolution of liquid crystal and plasma in different countries and regions is regarded as high-definition.

The resolution of HD TVs set by the Consumer Electronics Association ECA and the European Union of communications and household appliances (eicta) must be 1280*720 or more. According to the National HD standard published by the Ministry of Information Industry in April 5, the resolution of HDTV must reach 1280*720. That is to say, if the resolution of liquid crystal and plasma is less than 1280*720, HD TVs will no longer be called since January 1 next year.

LCD TV resolution can all be up to standard, but plasma can be full of excitement. The resolution of 42 inch plasma is as follows: 852*480, 1024*768, 1024*1024, and 1024*1080. Only 50 inch of plasma meets the national HD standard. What's more complicated is that the plasma 1024*1024 and 1024*1080 are not displayed row by row, but are emitting alternate lines, the above said, "We can think that liquid crystal and most plasma TVs are scanned on a row-by-row basis." That's why. However, you don't have to worry about this problem. Even if it is displayed across rows, it has no effect on the viewing effect.

In flat-panel TVs, especially plasma TVs that do not meet the requirements of the high-definition national standards are still said to be 1080p in promotional materials. This 1080 p is different from the 1080p we mentioned above. Taking Panasonic 42pa60c as an example, the physical resolution is only 852*480, which does not meet the requirements of the HD National Standard. The 1080 p mentioned by Panasonic means that 42pa60c can receive 1920 * 1080i signals, it can be processed in 1920 * P format. However, the resolution of 42pa60c is only 852*480, and 1920*1080 pixels cannot be fully displayed. Therefore, the resolution of the high-definition image is reduced to 852*480 and displayed on 42pa60c. This 1080p is not high-definition, but compatible with 1080 p.

Conclusion: for HD programs, the concepts of 720 p, 720 I, and 1280 p have no practical significance. 720,108 represents 1920*1080 0 represents, because even an image of I can be processed as P on a flat panel TV. For flat-screen TVs, 720 p, I, and P are meaningless. Flat TVs can all be regarded as line-by-line TVs. The resolution is determined by the resolution, according to the National HD standard, at least 1280*720 is required. Of course, the physical resolution of 1920*1080 is the best, but it has nothing to do with 720 p, I and P. The only concept that requires 720 p, I, and P is the HD camera. But for TV viewers, we only need to watch the program. As for what format the camera uses to photograph the program, it does not affect the viewing effect.

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