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Biography of the king of earth treasure

Electronic Cinematography (Volume Name: Movies)

Electronic cinematography

The technology of making movies by electronic means, mainly TV and video.

Before the invention of video recorder, recording and reproducing moving images mainly depended on photosensitive film. 1956, American Ampere Company successfully developed the first practical radio tape recorder, which recorded images with magnetic tape. This magnetic recording technology later developed into an extremely widely used image recording technology, and penetrated into film technology in many aspects, and even participated in and shared the production of the original film.

Magnetic recording is somewhat similar to magnetic recording. But its information recording capacity is as high as 100 times that of magnetic recording. The bandwidth of video signal is about 5 MHz, so it needs very high scanning speed to record this information. The vast majority of video recorders adopt the scanning mode that the magnetic head is mounted on the high-speed rotating head drum and contacts with the magnetic tape moving at a constant speed. In the first 20 years or so, almost all broadcast video recorders used 2-inch-wide magnetic tape, and the drum was equipped with four magnetic heads, which could scan horizontally on the magnetic tape. Each head only records 65,438+0/65,438+06 signals on each track. The relative speed of magnetic head tape is about 38 meters per second, and the speed of magnetic tape itself is about 38 centimeters per second. This machine is complicated, heavy, expensive and consumes a lot. After that, the magnetic recording materials were continuously improved. On the basis of improving the magnetic properties and reducing the granularity, the gap and recording wavelength of the magnetic head were shortened, thus reducing the relative speed between the magnetic head and the magnetic tape. At the same time, the development of large-scale integrated circuits and the use of digital time base corrector with large amount of correction have solved the time base problems of uneven speed and uneven track caused by longitudinal expansion and contraction of magnetic tape. At the end of 1970s, oblique scanning (or spiral scanning) 1 inch video recorder appeared. The relative speed of magnetic head tape is reduced to about 24 meters per second, the equipment structure is simplified, and the tape consumption is about 60 square centimeters per second, but the image quality level is still maintained at the same high level. Because of oblique scanning and long track, one head scans a track of a field signal, so it is easy to realize still frame, fast playback, slow playback and reverse playback, and the image search is convenient, which overcomes the editing difficulty of 2-inch video recorder. 1 inch video recorder is relatively simple, light and cheap, and has basically replaced the 2-inch video recorder, which provides a wide range of possibilities for expanding the production of video programs. Its portable video recorder weighs only a few kilograms and can be operated by batteries, which creates conditions for positioning and on-site shooting.

Making programs with tapes has many advantages, such as seeing the effect immediately after shooting, the tapes can be reused, multiple cameras can shoot at the same time, and monitors can be used to monitor from many places when shooting. Moreover, the video tape does not need to be developed, which saves the equipment, time and materials for development, shortens the production cycle and completely eliminates the pollution to the environment.

Video tape can record the time and control code similar to the film edge number. It can be displayed on the screen and automatically recognized by the machine for easy retrieval and control. Therefore, efficient electronic editing methods can be used in video production.

Video uses electrical signals, which is conducive to re-processing and even re-creation. For example, the image changes color, changes a specified part in the image, adds or deletes a certain part or information, and so on. Color key method is widely used in image synthesis stunts in TV video recording. For example, take the performance in front of the blue screen (other colors can also be used) as the foreground, and then take the background picture. When synthesizing, the blue part in the foreground automatically switches to the background part, so that the foreground and background can be synthesized. In addition, the image can be digitally decomposed into many pixels through digital stunts, and then combined according to certain rules or procedures to obtain various arbitrary three-dimensional graphic changes. The development of computer graphics methods has created conditions for using computers to process and even produce images, and the possibility of producing electronic images is often beyond people's imagination.

These characteristics of TV video make film and television workers produce the concept of electronic film photography when making movies by video recording. That is to say, we can shoot and produce programs by video technology and means according to the usual ways, techniques and tastes of movies, and then show them on large-screen projection TV, or turn them into movies and show them in cinemas by using the technology of "magnetic transfer adhesive" (see film and television image conversion). This method is limited by the information capacity of standard TV system, and its product quality is lower than that of film shooting. The "high definition" TV with horizontal scanning line above 1 thousand lines will be the main means of electronic film photography in the future, with the picture quality close to 35 mm film reprinting.

Video recording technology has been widely used in some fields of making programs with 16 mm film. At the end of 1960s, an oblique scanning 3/4-inch video recorder was successfully developed, which reduced the signal bandwidth and adopted the color recording method, that is, the chroma signal originally at the high end of the spectrum in the TV signal was placed below the low end of the brightness signal for recording. The relative speed of its head tape drops to about 10 meter per second. The tape consumption is about 18 cm2 per second. This machine uses two magnetic heads, and the magnetic tape is installed in the card holder, so it is very convenient to operate. Because of its light weight and low price, many departments that widely use 16 mm film, such as propaganda, education, training and scientific research departments, have gradually adopted video cassette recorders to produce programs. Because it is light and flexible, especially suitable for live shooting and news interviews, and the recorded material is available immediately, it is used instead of 16 mm film in most news interviews.

The mass production of civil 1/2 inch video cassette recorder began in the mid-1970s. Its basic structure is basically the same as that of the 3/4 inch machine, and it also adopts the color recording mode. In order to further improve the recording density and reduce the tape consumption, the original video tape is cancelled as a protective tape to isolate adjacent tracks and prevent crosstalk, and the crosstalk is eliminated by recording adjacent tracks and adjacent lines with different azimuth heads. The relative speed of the head tape of this video recorder is about 5.8 meters or 4.8 meters per second, and the tape speed is below 2.4 centimeters per second. In order to extend the recording time, some video recorders can record 8 hours of programs, and the tape consumption is as small as 1.4 square centimeter per second. 1/2 inch video recorder, low price, less tape consumption, suitable for home use, gradually popularized. The popularity of home video recorders has greatly increased the circulation of video tapes of film programs, making the transcription and reproduction of such videos an important business for various film development and printing departments in the world. Video tapes are easy to retrieve, and various archives departments have begun to convert film materials into cassette tapes for borrowers to watch.

Video recording can record sound at the same time. Video recorders are generally equipped with fixed recording and playback heads, and one or several audio tracks can be recorded at the edge when shooting video tapes. However, because the tape speed of 1/2 inch video recorder has been as low as 2 cm per second or even lower, the frequency response and signal-to-noise ratio of sound cannot be guaranteed. Therefore, the 1/2 inch video recorder later developed the same video head or a separate head to record sound on the rotating head drum, and inserted the sound carrier frequency in the gap of the image spectrum. Therefore, the sound quality of home video recorders has reached the level of high fidelity.

With the further development of science and technology, digital video recorder has been successfully developed, image processing technology is becoming more and more perfect, HDTV is about to become a reality, and integrated circuits are developing on a very large scale, which have created a solid foundation for the further realization of electronic film photography.

Yingshang County, Shi Ying

Film and Television Image Conversion (Volume Name: Movie)

Film-video image conversion

The process of converting image information on film into TV or video information and the reverse process of this conversion. Movies and TV videos are two widely used moving image recording and transmission media, and they are closely related. On many occasions, the program of one media should be converted into another media to adapt to different display modes or meet the needs of mutual utilization of certain technical processes. Film and television image conversion is an important business content of modern film processing and printing plants.

The principle and method of image synthesis between film and TV are different, and some special problems need to be solved in the process of mutual conversion. A movie is to shoot a complete picture on film, 24 frames per second. When two adjacent squares change, it takes about 20 milliseconds to change the shadow label. During the screening, a complete picture is projected on the screen, and shadows are added twice every frame, which takes a long time to pull the tab. Television is the horizontal and vertical scanning of high-speed electron beam on the target of camera tube, which picks up the charge generated by the optical image irradiated on the target surface and turns the information of spatial function into the information of time function; Through the horizontal and vertical scanning of the electron beam modulated by the video signal, the image is displayed on the screen of the picture tube. Therefore, TV images are composed of many rows of pixels arranged horizontally from top to bottom. Ordinary TV scanning standards are divided into 625 lines per frame, 25 frames per second, and 525 lines per frame, 30 frames per second. In order to reduce flicker, they all adopt interlaced scanning, and divide each frame into two fields, odd field and odd field, with half the number of lines in each field (figure 1), so the 625-line system has 50 fields per second and the 525-line system has 60 fields per second. The electron beam is blanked at the end of each line and each field, and is not displayed. The blanking period is only a fraction of the display time, which is very short, and the field blanking period is about 1.6 milliseconds.

In order to coordinate the conversion between film and TV, and eliminate the possible black bars when the number of TV frames is inconsistent with the number of movie frames, when the 25-frame TV system and the movie are converted to each other, the movie speed is generally changed to 25 frames per second, and the speed is increased by about 4%. This has little effect on sound and video action. The conversion of 30-frame TV system is complicated. When a movie is converted into TV, there are usually 5 TV fields every 2 movie frames, and 24 movies are converted into 60 TV signals. Television to movies is just the opposite. One or two half-field signals must be deleted every five scenes and recorded on two film frames. The time of shading pull-tab of film is much longer than the blanking period of TV signal field. In order not to lose the image during the conversion, these two times need to be adjusted to match them.

Many mechanical and optical methods are used to solve the above problems, such as the use of special devices, such as quick pull-ring mechanism and five-leaf shutter. Since the 1980s, electronic technology, especially the use of digital frame (field) memory, has made it possible for some conversions that were not easy to do in the past. The working principle of frame memory is to decompose each frame image into many pixels line by line, and the brightness and chromaticity values of each pixel are digitally stored in the corresponding storage unit of digital frame memory, and then read out according to the special requirements of the conversion process. The reading mode and speed can be inconsistent with the storage (writing) time, so various required transformations can be obtained.

The conversion between movies and TV videos can be divided into the following categories:

Tape-to-film is to copy video information from TV or video tape to film. Under the common 625/50 or 525/60 TV standards, the information content of a frame of image is only about one-fifth of that of 35mm film. The following methods all have the ability to transfer all the information of ordinary TV recording to film, but the quality of magnetic transfer film is lower than that of 16mm film. ① Screen recording. That is, use a camera to shoot a high-resolution color monitor screen. This method is simple and widely used. The more professional departments adopt the three-tube screen recording method, that is, three monochrome (red, green and blue) picture tubes with higher definition than color displays are used to display the red, green and blue components of video signals respectively, and then a color image is synthesized by dichroic mirrors for shooting. I also used a single monochrome kinescope to display the red, green and blue components of a video tape in turn, shot three black and white color splitters, and then printed the embossed film to make a printed copy. When recording 16 mm movies on the screen, you can use a pneumatic quick pull-tab camera, and the pull-tab time is close to 1 millisecond. When using 35mm film, a frame memory is needed, which can make the image read faster and leave more blank time, so it can match the longer pull-up time required by 35mm film. Deleting the corresponding TV field during reading can also solve the problem of video conversion between 24 frames and 30 frames. ② Electron beam video recording. Exposure latent image can be produced by bombarding photosensitive film with electron beam. The film is placed in a vacuum box equipped with an electron gun, and the electron beam is modulated by the video signal and focused on the black and white film to produce an image latent image. After the video signal of the video tape is processed and stored in the intermediate medium, the red, green and blue signal components in each frame are sequentially taken out at the speed of 72 frames per second (3×24), and the film is exposed by an electron gun. Therefore, every three adjacent squares on the film respectively represent one of the three primary color components in a frame signal. After cleaning, use a special printer equipped with a red, green and blue color filter turntable to print the color film according to the principle of black-and-white color separation and synthesis: every three frames of the printer's projection head, the camera pulls 1 frame, the red component film is exposed once through the red filter, and the blue and green component films are exposed once through the blue and green filters respectively to synthesize a complete color film. The video signal is changed from interlaced scanning of two fields to progressive scanning of one frame, so the film can be continuously fed by the precision servo system without intermittent exposure. Electron beam method has almost no scattering and halo phenomenon, strong energy, low sensitivity and high definition. Its capacity has exceeded the requirements of the standard information capacity of ordinary TV. By transcribing HDTV signals with more than 65,438+0,000 lines per frame in this way, a film with a reproduction quality close to that of ordinary 35mm can be obtained. (3) Laser scanning video. The laser beam modulated by video signal is scanned on the film to produce image exposure, as shown in the figure, He-Ne laser produces red light, argon ion laser produces green light and He-Cd laser produces blue light; Red, green and blue video signals are sent to a crystal acousto-optic modulator to modulate the laser beam passing through them; Three beams of light are combined by a dichroic mirror and projected onto a high-speed rotating polygon prism. Because the mirror deflects the reflected light beam once per side when rotating, the product of the number of prism faces and the number of revolutions per second is equal to the line frequency of the video signal, so horizontal deflection occurs. The beam is reflected by the field frequency galvanometer, resulting in vertical deflection. When transcribing 16 mm film, you can shoot with a quick pull-tab camera, but when converting to 35 mm film, you usually use continuous exposure mode. At this time, you need to use the frame rate galvanometer to deflect vertically to produce the raster jump scanning effect, which can overlap and merge the exposure of odd and even fields in the film. It is also possible to store interlaced signals in a frame memory and then take them out line by line and convert them into progressive scanning to meet the requirements of continuous exposure. The laser beam has pure chromaticity and high energy, and can be focused into a very fine beam, which can be directly exposed on the granular color film, so the image quality is high and the processing technology is simple. The potential of this method has also exceeded the requirements of ordinary TV standards. When recording HDTV signals, 35 mm film with quality close to ordinary film can be obtained (Figure 2).

Film-to-tape is the signal form needed to convert the image on film into TV or video tape. This conversion equipment is collectively called TV movie projector. With the progress of science and technology, in the process of film production, TV video recording technology is often needed as an auxiliary means to improve the efficiency of film production and save money. There are several ways to turn rubber into magnetism: ① Combination of projector and camera. The basic principle is to use a TV camera with a photoconductive camera tube to shoot the images shown by ordinary movie projectors through relay optical elements. Because the photoconductive camera tube has the image storage function for a certain time, even if the shading time of the projector is much longer than the blanking period of the TV field, some images will not be lost in the shot TV signal. However, the photoconductive camera tube has delayed tailing phenomenon, which is not good for fast-moving images. Optical steering mirrors can be used to switch between several projection devices. Medium-quality TV movie machines mostly use non-intermittent rotating polygon mirrors or multi-lens continuous projection. ② Flying spot scanning mode. Use cathode ray tube as light source. After scanning the film vertically and horizontally, the light spot on the grating is decomposed into three colors: red, green and blue, which are projected on the target surfaces of three photomultiplier tubes respectively, and their output signals are processed, corrected and coded into TV signals respectively. The flying spot scanning system has no image storage function, so the image has no delay and tailing, but it can only be shown by a special 16 mm projector, and the time for pulling the tab is short. For 35mm film with large inertia, continuous film feeding must be adopted. At this time, in order to change a frame of the film into the odd-even field required by the TV signal, it is necessary to scan the same frame on the moving film twice. Therefore, it is necessary to generate gratings before and after the film moving direction. Grating and film move in opposite directions, and the whole frame can be scanned at half height, so it is necessary for the half-height grating to change its position alternately at the frame rate. If the frame memory is used, the moving film can be scanned continuously with a fixed grating. After the signal is stored in the frame memory, it can be read out according to the requirements of interlaced scanning, so that odd fields and even fields can be generated. You can also read some lines repeatedly, and convert 24 frames of movies into 60 TV signals, thus solving the problem that in the past 60 TV systems, flying spots could hardly be used to scan TV movies. Frame memory can also be used for stepless speed change or freeze-frame operation, which can adapt to the special requirements of some films or produce special effects. (3) the scanning mode of charge coupled devices. The continuously running film is irradiated by incandescent light, and then divided into three beams of red, green and blue by beam splitter, and projected onto three linear charge coupled devices. Thousands of semiconductor photosensitive elements are arranged on each device, and their output signals are proportional to the irradiation intensity. Scan the image horizontally with a clock pulse and take out the information on the components in turn. Vertical scanning is formed by the continuous motion of the film. The output signal is stored in the frame memory after processing, and then taken out according to the requirements of signal form. ④ Laser scanning mode. Similar to the laser scanning magnetic transfer method mentioned above. The red, green and blue laser beams are combined by a dichroic mirror, horizontally deflected by a high-speed rotating polygon mirror, vertically deflected by a vibrating mirror and tracked by a grating with a tracking deflector. After scanning the film, the beam is decomposed into red, green and blue light by the beam splitting system, and projected onto their respective photomultiplier tubes to generate signals. Laser has high color purity and strong energy, and can be focused into a very fine spot, so the image clarity and color are better. This method is suitable for HDTV system and 70 mm film.

Due to the comprehensive decomposition characteristics of TV movie projection system and the limitation of TV image viewing conditions, TV movie system can't reproduce the tone of the whole density range of movie images, and the shadow level is lost, and the color saturation and fidelity are reduced. Therefore, it is best to use low contrast film for TV movies. In addition, the modern TV film projection system can be directly converted from negative film, which has low contrast and rich layering, so the quality after conversion is high, which can avoid the increased quality loss in the process of developing positive film from negative film.

Television and film projectors can correct the color of the scenes one by one, preview the color balance of the film in advance in a way similar to the light distribution during development and printing, call up the best state, record the correction values in the microcomputer, and control each scene in the formal conversion process. Television film projection equipment can be equipped with a device similar to "wet film printing" (see film printer), and the scratch effect on the film can be eliminated by using the liquid film door. Electronic methods can also be used to reduce the granularity of the film and cover the spots.

The black-and-white film coloring method can electronically convert monochrome image signals of black-and-white films into color TV signals. This change can improve the artistic effect and ornamental value of black and white films made in the early days. In this way, we can combine the technology of the 1980s with the art of the 40s, and make the old movies glow again.

When coloring, first determine the color requirements of the film, determine the coloring of the first frame in each scene and the frame with great changes in the same scene, and automatically color the remaining frames in the scene by imitating this frame. The whole process is electronic. Each color area is divided by the electronic drawing board, and the corresponding hue with appropriate concentration is added to each area by the electronic palette. The brightness signal of the initial frame is digitized into pixels containing the brightness value and its coordinates. The computer tracks all parts of the image by comparing the pixels of the next frame or making logical judgments through complex software, and matches the same tone in the corresponding parts of the previous frame. In the case of exceeding the judgment ability of the program, it is sometimes necessary to turn to the operator for help. A color image signal can be obtained by combining the original brightness signal with the hue.