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Vertical definition: Since the term "vertical definition" is easier to understand, we start with simple things. "Vertical resolution" is the number of pixels in an image from top to bottom. Since each horizontal scan line forms a vertical pixel, we can also say that "vertical resolution" is how many "horizontal scan lines" an image consists of. The number of horizontal scan lines in an image is determined by the signal format, so as long as the signal format is defined, the vertical resolution is determined. For the PAL system, whether you are watching TV shows, VCRs, VCDs, LDs, or DVDs, the vertical resolution you see at the end is 625. Further, the picture we see is not composed of all 625 lines. In fact, during the blanking period, there are 49 lines for transmitting other information, such as closed captions, graphics, test signals, etc. At the same time, when the electron beam is returned from the bottom to the top to start scanning the next image, it still needs some time. Remove the highest vertical resolution of these PAL systems. Further, due to the imaging reasons and human visual characteristics, these 576 lines are only the theoretical resolution. The actual vertical resolution of the image you "see" must also be multiplied by a correction factor less than 1, which is called the Kell coefficient. For interlaced scanning, the Kell coefficient is 0.7, so for the PAL system, the vertical resolution of the last displayed image is about 400 lines. When actually viewing the test chart, the observed vertical resolution can usually reach about 450 lines because the Kell coefficient is not considered.
Horizontal Resolution: As we mentioned earlier, vertical resolution is completely determined by the signal format, which is very easy to understand. Horizontal definition is the most easily confusing concept. The biggest problem is that there are multiple expressions of horizontal definition. Some IT industry people, who know the resolution of computers, do not know how to use the term "resolution" in home theaters. This is because multiple expressions can be expressed in a wide variety of data. In different situations, the same data may represent completely different performance. The computer field in the computer industry often uses the number of pixels that make up an image to indicate the resolution, that is, the number of horizontal pixels×the number of vertical pixels. Such as: VGA: 640 × 480; SVGA: 800 × 600; XGA: 1024 × 768. But in the video field, we are more accustomed to using the “per image height†pixels to represent horizontal resolution, and call it “TV lineâ€. The origin of this habit dates back to 60 years before the television was born. At the time, because the format of the signal had determined the vertical resolution of the image, the experts' idea was to represent horizontal resolution in a manner that was related to vertical clarity. In other words, whether it is clearer in the horizontal direction or clearer in the vertical direction can be clearly seen through this relative clarity. For this reason, the horizontal definition (TV line) is defined as the number of pixels that can be displayed in the horizontal direction that is equal to the screen height. The definition obtained under this definition is called the "TV line." Therefore, when you still hear how much clarity a video signal has, it doesn't mean how many pixels are from the leftmost to the rightmost edge of the image, but how many pixels are in the same horizontal width as the height of the image. Take a look at your television or computer monitor. You will find that they are not boxy. The display ratio is 4:3. In other words, to achieve the same horizontal resolution with vertical resolution, the pixels in the horizontal direction should reach 4/3 times the vertical resolution. For DVDs, the NTSC system is 720 x 480 pixels and the PAL system is 720 x 576 pixels. The horizontal resolution of NTSC and PAL systems is 720×3/4=540 lines. On NTSC DVDs, horizontal resolution is higher than vertical resolution (540 lines > 480 lines); on PAL DVDs, horizontal resolution is slightly lower than vertical resolution (540 lines > 576 lines).
The determinants of sharpness: image clarity = image quality of the signal source × processing level of the processing circuit × development quality of the display method. All three factors are equally important in determining the final image quality. Any difference in the links will result in a decrease in the horizontal resolution of the final image. Even if some products have improved processing circuit performance or imaging performance, they cannot significantly improve image quality without corresponding signal source cooperation.
The relationship between the bandwidth and the pixel is analog signal, to be displayed on the digital display device, we must first carry out the analog → digital conversion; and if it is a digital signal, to be displayed on the analog display device, we must first conduct the digital → Analog conversion. In the field of analog signals, we use bandwidth to represent the quality of the signal. In the field of digital signals, we use the number of pixels that make up an image to represent the quality of the image. The video bandwidth of the PAL signal is 6 MHz. After standard digital sampling, a 720×576 image is obtained, both of which represent the same quality of image. Just as we describe a dish of food, Chinese speaks of “good food†and English says “deliciousâ€. The meaning is the same.
Calculate the horizontal resolution from the pixel: VGA (640×480, 4:3 screen): 480 lines; SVGA (800×600, 4:3 screen): 600 lines; XGA (1024×768, 4:3 screen): 768 Line; 720P (1280×720, 16:9 screen): 720 lines; 1080I (1920×1080, 16:9 screen): 1080 lines.
The resolution of horizontal resolution from bandwidth is H=2×T÷A×F. Where T is the horizontal scanning duration, it is fixed for a certain TV image format; A is the aspect ratio of the picture tube (4:3 or 16:9), F is the extension bandwidth of the TV, T and A Is a constant. In terms of PAL system, the maximum bandwidth of this signal is 6MHz and the line frequency is 15625Hz/s. If the image signal is the highest frequency of 6MHz single frequency, then each line can display 6000000/15625=384 weeks. If the positive half is white and the negative half is black, 768 black and white lines can be displayed for each line period. Each row cycle is further divided into a positive range and a retracement, and only the forward range contributes to the resolution. The PAL system has a horizontal retracement of 18%, so the total number of black-and-white lines that can be displayed at most in each line does not exceed 768×0.82=629.76. In other words, the limit of the horizontal resolution power of the PAL system is 630 black-and-white lines, and the conversion to television lines is about 470 television lines. Of course, it is not necessary to calculate so complex every time. An empirical algorithm can be used to calculate: 1 MHz bandwidth = 81 TV lines. This is not difficult to find - VHS recorder: 3MHz bandwidth, 240 lines; NTSC TV: 4MHz bandwidth, 320 lines; PAL TV: 6MHz bandwidth, about 480 lines; DVD: 6.75MHz, 540 lines or so.
Popular data and terminology interpretation 1250 lines, 31250 lines, 30MHz bandwidth, 2 million pixels, ultra-fine picture tube, these are the popular data and terms that the salesman "sell" to you. If you do not read this article, you may be confused. Now that we have the foreshadowing of previous knowledge, we can uncover these data nouns and veils. Similarly, the word “line†may be referred to as “horizontal scan line†(vertical definition), or may be the total number of lines on the entire screen in the horizontal direction, or the number of lines in the horizontal width of the screen height. (TV line). 1250 line This is a special term for frequency-doubled scanning televisions. Since the frequency of frequency-doubled scan field scans has doubled, the original 625 lines per frame have now become 1250 lines, hence the so-called 1250 line, where the “line†refers to the horizontal scan line. 30MHz bandwidth According to the method we introduced before, we can calculate that the 30MHz bandwidth is 1920×1080. It should be noted that for the PAL signal source, the bandwidth is only 6 MHz. At this time, it is wasteful to use a processing bandwidth of 30 MHz, and it is impossible to improve the image quality. Because even with 30MHz bandwidth, there must be a 30MHz signal source (HDTV), and a picture tube capable of displaying 1920x1080. Without these two support, 30MHz is just a deafening data. If the source of the television is 720×576 (415,000 pixels), even if the processing performance is better, the final image is still 720×576 (415,000 pixels). In the "2-megapixel" process, every 5 pixels are actually exactly the same pixel. And don't forget that the display method of the three elements of the image clarity we previously counted, although it was processed by 2 million pixels, but the final tube is still an ordinary tube, it still can only display 720 × 576 (41.5 Megapixel), so even if it is 200 million pixels, it does not improve the image quality at all. So, 30MHz bandwidth and 2 million pixel processing are the same meaning. Only 30MHz follows the traditional analog signal processing terminology, and 2 million pixels is a popular term for "digital upstarts." The two nouns actually express the same performance indicator.
Screen Segmentation 1/4/9/16/25/32/64 Screen Segmented Pixels Composed of Images: Images are composed of successive, fast-moving still images. When we talk about the resolution of an image, we refer to the pixels that make up the image. Think about drawing paper, when you fill in the corresponding color in each grid, you get a picture. Pixels compose lines, lines form a picture, and many pictures form an active image in succession.