Pixels(pixel): A pixel is usually regarded as the smallest completeness of an imagesampling
If we magnify the image several times, we will find that these continuous tones are actually composed of many small square dots with similar colors, which are the smallest unit "pixel" that constitute the image. This smallest graphic unit can display on the screen, usually a single dyeing point. The higher the pixel, the richer the color plate it has, and the more it can express the authenticity of the color.
For example, "640 by 480 display", it has 640 pixels in landscape and 480 pixels in portrait (like VGA displays), so its total number is 640 × 480 = 307,200 pixels.
For TV videos, dozens of still images are included per second, each still image consists of hundreds of rows, and each row consists of hundreds of pixels. The number of frames in the image contained in 1 second is the frame rate, the total number of rows in 1 second is the row frequency, and the total number of pixels in 1 second is actually equivalent to the video bandwidth.
From the perspective of frequency domain, the chromaticity signal (UV color difference signal) is inserted in the gap in the spectrum of the luminance signal, and the specific position is inserted at 4.43MHz and the bandwidth is 1.3MHz. In the receiver, simply speaking, the signal with a bandwidth of 1.3MHz at 4.43MHz in the received signal becomes a chrominance signal, and the signal at 4.43MHz in the received signal is filtered out and the remaining luminance signal is the luminance signal.
How to restore and display color images: RGB (red, green, and blue) three primary colors are synthesized using the CRT display tubes of computers or TVs.
In a television, the color video signal is first decomposed into the brightness signal Y and chromaticity signals, and the chromaticity signal is then decomposed into the U color difference signal and the V color difference signal. Finally, the three components of YUV are converted into RGB signals through matrix operations for display on the imaging tube.
Why use YUV to transmit instead of RGB (Note: Finally, display it in RGB): 1 is compatible with black and white images, 2 saves bandwidth, and 3 has strong anti-interference ability.
The CCIR601 standard is mainly formulated for studio requirements, where the sampling frequency of the luminance signal is 13.5 MHz and the sampling frequency of the chrominance signal is 6.75 MHz, and is encoded by 8-bit PCM. In this way, the number of Y samples per row is 864, of which the number of valid Y samples is 720. The number of U or V samples per row is 432, and the number of valid U or V samples is 360. The average number of bits of YUV describing each pixel is 8 bits, 4 bits, and 4 bits, which is also called the YUV422 encoding scheme (of course there are many other schemes, such as YUV411, etc.). The International Radio Advisory Committee also issued a CCIR656 recommendation, which stipulates that 0 and 255 of the quantized values of video data are reserved, and the sequence of serial output of the quantized data is: U0, Y0, V0, Y1, U2, Y2, V2, Y3, U4, Y5, V4, Y6, and this cycle is performed. Through the above discussion, we can see that the elements that digital video stream should contain are: parity field indication signal FI (some are called ODD), field synchronization signal, row synchronization signal, pixel clock, and YUV data output. Here we calculate the data volume of the digital video stream. The data volume per second = (720 pixels * 576 rows * 25 frames) * 2 bytes = 20736000 bytes, and the data rate is about 165Mbps. This shows how large the data volume of the digital video is and how high the data rate is!