What is 4k video? Bian Xiao takes you into the 4k world.

From HD to 4K, it is the general trend of TV technology development. This paper analyzes the innovation and development of TV technology system brought by the development of 4K technology from the perspectives of camera technology, studio system reform, audio and video post-processing reform, etc., which fully shows that it will be a huge technological change from HD to 4K.

1. Performance comparison

Some manufacturers' representatives talked about the advantages of 4K TV over HDTV, that is, higher resolution, higher frame rate, wider color gamut, wider dynamic range and greater quantization bit depth.

Resolution (spatial resolution), that is, the number of pixels contained in an image within a specific spatial range. The more pixels, the clearer the image. The resolution of ordinary HDTV is 1920× 1080, while that of 4K ultra-HDTV is 3840×2 160. Obviously, 4K TV has higher definition than HDTV, which can bring more realistic visual experience to the audience.

Color gamut (color resolution), that is, the sum of colors that a technical system can produce. Now HDTV adopts ITU BT.709 color gamut, and its area is 33.5% of the visible spectrum. 4K Ultra HD TV adopts ITUBT.2020 color gamut, and its area is 63.3% of the visible spectrum. A wider color gamut means richer colors, stronger color saturation and more realistic color reproduction.

Dynamic range (tolerance resolution) refers to the ratio of the brightness of the brightest part to the brightness of the darkest part in the picture. The dynamic range of existing HDTV is based on the performance of CRT, which we can call standard dynamic range (SDR). After a series of processing, this range is only 10 3: 1, that is, 1000: 1, which is far less than the brightness range that human eyes can perceive, and a lot of brightness details are lost. HDR (High Dynamic Range) technology of 4K TV aims to make the dynamic range reach the brightness range that human eyes can see without adjusting pupils, that is, 10 5: 1. Intuitively speaking, it is to keep the details of highlights and shadows in the picture as much as possible, so as not to be overexposed and completely black, so that we can see more details of the light and dark parts of the picture.

Frame rate (temporal resolution), that is, the number of frames contained in the video per second. The higher the number of frames, the smoother and more natural the picture will be, otherwise the picture will be incoherent, occasionally accompanied by motion blur, tailing and jitter. The existing HDTV generally adopts the mode of 25 frames per second and interlaced scanning. 4K Ultra HD TV will replace interlaced scanning with progressive scanning, with 50 frames per second, up to 120 frames, and the picture quality of moving images will be greatly improved.

Quantization bit depth (gray scale resolution) means that digital technology reproduces the gray scale changes of analog images with limited gray scale. HDTV is generally 8 bits, and 4K TV is generally 10 bits.

Color space is a cube composed of color gamut and gamma, which is used to vividly describe the color, brightness and contrast performance of shooting and display. Obviously, 4K TV adopts BT.2020 color gamut and HDR gamma, which has a wider color space than HDTV.

2. Comparison of mainstream coding and code rate.

In terms of resolution, the amount of data in 4K is four times that in HD (at the same frame rate). For example, 4K 25p is equivalent to 50i in HD. In terms of frame rate, the frame rate of 4K 50p is twice that of HD 50i. Combining resolution and frame rate, the data volume of 4K is 8 times or even higher than that of HD. For example:

From HD to 4K, this is a very challenging change in the history of TV technology. This change involves technological changes in all aspects of TV editing and broadcasting, and the innovative development of camera technology is bound to bear the brunt.

1. Technological change and development

Traditional high-definition cameras generally use 2/3 inch imaging equipment, BT.709 color gamut and TV gamma, and the photos taken are what you see is what you get.

There are mainly two kinds of 4K cameras: one is a single-chip large-format 4K imaging device with PL lens bayonet, which shows shallow depth of field and pursues film art style; The other uses three 2/3 inch 4K imaging devices and B4 lens bayonet, and the shot picture is Quan Jingshen, which meets the requirements of live TV broadcast. Both models have BT.2020 color gamut and BT.709 color gamut, and have different types of gamma curves, which can meet the requirements of HDR shooting.

Brief Introduction of Several Mainstream Models of 2.4K Camera

Sony released two hand-held cameras PXW-Z 190 and PXW-Z280, both of which support 4K shooting, have powerful HDR processing capability, and are compact and easy to carry. Among them, Z 190 is equipped with 1/3-inch Exmor RCMOS imager, which can shoot 4K 50p/60p, is compatible with HLG and supports Sony HDR workflow; The Z280 is equipped with three brand-new 1/2-inch Exmor RCMOS imagers, which can help users to achieve high sensitivity of f12 (59.94p)/f13 (50p), long zoom ratio and deep depth of field shooting, stepless nd filter and advanced autofocus (AF) function.

In addition, at present, CCTV mainly has camera models such as Sony PMW-F55 and Panasonic V35. Among them, the performance characteristics of Sony PMW-F55 are: 35mm 4K CMOS imager, 14 file tolerance, high sensitivity, low noise, wider dynamic range and color gamut. The main features of Panasonic V35 are: high-performance viewfinder, auxiliary focusing function that can monitor the overall focus of the picture, built-in color adjustment function of the camera, AVC-ULTRA4K 4:4:4( 12 bits) high-quality compression coding, 4K/ 120p original data recording, etc. Using these cameras, the production of large-scale 4K programs such as Spring Festival Evening 20 16, Long March Forever, Spring Festival Evening 20 17 and g 20 Summit Welcome Meeting was completed, which made full preparations for the production and broadcasting of 4K programs.

After the upgrade, a 4K virtual PGM synthesis system is designed and established. The system is mainly composed of 4K multi-channel recording server, virtual switching and 4K synthesis server and 4K playback server. It can automatically obtain the cut-off information, switching stunt information and current time code information of the high-definition switching station, and automatically generate 4K PGM content corresponding to high definition for the included 4K materials. After the program is recorded for 6 seconds, a 4K version of video and audio files can be formed. Compared with the original method of artificially comparing HD programs to produce 4K programs, the system greatly reduces the labor cost, shortens the production cycle, improves the production efficiency of 4K programs, and makes full preparations for the production and broadcasting of 4K programs. At present, the system has completed the 4K version recording of 20 18 CCTV Spring Festival Evening, 20 18 Lantern Festival Evening, Avenue of Stars, ingenious dreaming, straight to the point and other programs.

1. Color matching is a key link in video post-production. Because the high-definition camera adopts TV gamma and BT.709 color gamut, the pictures taken are what you see is what you get, so there is generally no need to restore and correct the color of the shot material, only a small amount of color adjustment is needed as needed. For 4K camera, in order to keep all the details of highlights, middle levels and dark parts of the picture and achieve high dynamic range, log logarithmic shooting mode is adopted, which makes the shot material picture dark and opaque. In the later stage, color restoration and correction must be carried out, and color adjustment should be carried out as needed to make the picture more vivid and colorful. Sometimes, according to different types of programs, artistic stylization is needed. Therefore, different from HD production, the color matching of 4K production is the key link of the whole post-production, which needs people with professional color theory knowledge and rich practical experience to complete.

2. Nesting process is more common.

For the post-production of 4K programs, it is mainly divided into two technological processes: the first is to edit the XAVC file shot by Sony 4K camera (such as F55) in Apple FCP X fine editing software, then color the edited project, add packaging, special effects, shoot lyrics, and finally output the finished file; Second, for the RAW file with large bit rate, firstly edit the high-definition proxy material, upload the edited material from the hard disk corresponding to the project, and then perform color matching, special effects, subtitle synthesis, etc. And finally output 4K movies. Among them, the secondary editing mode is more common, which not only ensures the fluency of production, but also greatly improves the efficiency of later video editing.

1. surround sound production

Different from the process mode of stereo production in HD, 4K programs need to produce surround sound, that is, while producing left and right channel stereo, they also need to produce surround sound of left front, right front, center, bass, left back and right back, so as to ensure that the audience can feel the shocking effect brought by the program sound from multiple angles.

The specific process is as follows: first, the actual sound and stereo reference sound shot and recorded in the studio or outdoors are transmitted to the video post-production island, and the complete audio material is transmitted back to the audio production island. In the later stage of video, the sound picture is edited synchronously, and the edited "n version of Mix 5. 1+ST" is laid on the time axis and transmitted to the audio production island. N versions of this film, its EDL information file, new material AAF file, etc. Also transmit together. The audio island processes all audio materials according to the program film and EDL information, and finally transmits the produced audio files to the later video for video-audio synthesis and output to the film.

2. Three-dimensional sound generation

With the development of 4K technology, TV programs sometimes adopt the audio production mode of TV stereo to enhance the audience's audio-visual experience. TV 3D sound is produced and played in 5. 1+4H format, including technologies such as cloud computing, database and big data analysis. By using technologies such as 4G transmission, streaming media transmission and mobile live broadcast, content resources are integrated, data storage and mining capabilities are improved, and the efficiency and stability of information dissemination are improved. Fifth, establish an institutional mechanism to adapt to the deep integration and development of media, give full play to the role of market mechanism, explore the road of media integration and development with capital as the link, adhere to the drive of open innovation, actively explore various profit channels such as advertising management, information service, copyright cooperation, etc., and make concerted efforts to make new media brands live through network planning. The number of fans, attention and clicks have greatly increased, and the high-quality content and platform traffic of Guizhou Taiwan have been transformed into practical benefits.

The development of TV technology, from high definition to 4K, will be a great change. This change, from camera technology to studio system, and then to later audio and video technology, will be a complete technological revolution. The whole change from China to the world will bring about the innovation and development of the global TV technology system, and make the future development of the whole TV industry more dynamic.