Look at the information on this website.
1. DSP digital processing technology
Since 1990s, human society has stepped into the information age, and an important feature of the information age is the popularization of digital products, among which the most typical is the technology with DSP as the core and its product application. DSP is the abbreviation of digital signal processing, but its development has gone beyond its superficial significance and become a new digital processing technology. Its characteristic is the successful application of DSP in camera, which opens a new chapter of modern camera technology and becomes another epoch-making application achievement of new camera technology after CCD.
DSP digital signal processing technology is a comprehensive scientific research achievement of digital signal processing, microelectronics, computer science and computer mathematics. DSP chips have been widely used in many fields, such as magnetic drivers, cellular phones, modems, radio receivers, microcontrollers, CD players, digital cameras and digital video cameras, and will be applied to most electronic devices.
The application of DSP digital signal processor in color camera makes it one of the core components of the whole system. Its function is to optimize the digital image signal through a series of complex digital algorithms, including white balance, color balance, gamma correction, edge correction, etc. These algorithms will directly affect the quality of the image signal.
As far as any DSP chip is concerned, it is essentially a single chip microcomputer, which is only specially used to process digital signals. Its biggest feature is its extremely fast operation speed, which is two orders of magnitude faster than that of ordinary microcomputers, and it can complete complex and tedious mathematical operations in a short time. DSP digital signal processing camera technology was developed in the mid-1990s, and was first applied to VHS-C format cameras. Figure 3-8 1 is such a camera.
In the picture, the image signal sent by CCD camera is converted into digital signal by A/D, and then sent to DSP digital signal processing integrated circuit. In the integrated circuit, the white balance of Y/C is adjusted first, and then the digital signal sent by Y/C processing circuit is digitally scaled and stored in the frame memory. At the same time, the digital zoom processing circuit can take out the enlarged or reduced image signal from the frame memory according to different proportions and send it to the autofocus processor. After analyzing the main frequency components in the signal, control the motor to adjust the lens distance.
In practical application, an important problem is the jitter of the operator's palm. Because of shaking, it is almost impossible to make the image unstable without shaking the palm. Therefore, this problem must be solved in the circuit of camcorder, and the fuzzy image stabilization processing in the circuit is specially designed to solve this problem. In the figure, the signal processed by Y/C is sent to the motion detection circuit to detect the motion state of the image. Through fuzzy logic analysis, it is judged whether the motion of the image is caused by hand trembling. According to the degree of hand shake, the circuit determines that the hand shake causes the jitter, and then chooses to read the image information from the memory to offset the image jitter.
After the above digital processing, it is converted into an analog video signal through D/A conversion, which is sent to the recording system and recorded on the magnetic tape.
After several years of research and development, DSP camera technology has matured. At present, the top models represented by major camera manufacturers have adopted DSP camera technology. For example, Sony's 3CCD DSP color camera DXC—D30Pjiushi is a prominent model (as shown).
Second, all-digital video processing technology.
At present, there are still some analog processing circuits in digital cameras. The development direction is full digitalization of video signal processing, and the key is development and production.
Bit analog-to-digital converter. At present, the latest generation is 14-bit DSP digital signal processing cameras, such as DYC DY-90EC and DY-70EC (D9 format), Sony DSR-PDX 10P(DVCAM), and Panasonic 50-city DVCPRRO50 AJ-D900.
The core of digital video processing technology is digital video coding and decoding technology. Before the early 1990s, no one believed that video information could be processed digitally, but this traditional understanding was broken when the video compression technology made great progress. Now, digital video has been widely used, for example, digital TV can be transmitted to the home through satellite and terrestrial network. Video mail and family on the Internet are video games; Transmitting video conference on telecommunication network; Computer network remote video teaching, etc. All this benefits from the development of video compression technology.
1 Introduction. MPEG compression principle
Digital video compression is to remove redundant information from a series of images, which greatly reduces the amount of data, but the human eye does not notice the change of image quality after decompression. Digital compression is usually called encoding, and decompression is called decoding. MPEG is the most common video coding method nowadays, among which MPEG-2 is formulated for rate applications (such as TV and DVD). ). MPEG-2 coding has two main steps:
In each frame of image, block coding technology is used for spatial compression. For example, the human eye is not sensitive to the image information reflected in the dark background, so it can compress most of the big dark background in the frame.
Time compression is performed between adjacent frames of an image to remove redundant information between frames. This step is called dynamic judgment. For example, a bird flies in the air, and only a bird flies in a frame, but the sky background in a large area is basically unchanged, and there are similar inconvenient information between frames, which can be compressed.
In the encoding process, the encoder first determines whether the input video frame is dynamically compressed or block-coded compressed, and then encodes it to remove redundant information.
2. Digital processing of video signal.
Digital processing of video signal is an inevitable development trend, which has been developing in this field since 1990s. For example, Panasonic's AQ-20 and AQ- 1 1 digital processing cameras are considered as the representatives of the first generation of digital cameras.
Digital cameras have the following characteristics:
Improve stability, because the data storage is realized, these data will not change with time and temperature, thus achieving high stability of various controlled variables.
Some new functions have been added, such as automatic shadow compensation, color detail compensation and computer-controlled gamma correction.
Some operational performance has been improved.
At present, digital video processing technology has greatly surpassed the traditional analog processing technology, and will be completely modernized in the near future.
3. 12 information technology and new functions of digital cameras
All-digital video camera records digital video and audio signals on magnetic tape or hard disk, which needs to process a lot of information. Therefore, new high-density recording methods, data compression technology and large-capacity integrated circuit memory should be adopted. One of the main advantages of all-digital video is that it can be copied many times, easily edited and copied repeatedly, and can be connected with a computer for image processing. In addition, the continuous introduction and development of new technology applications have significantly improved the overall performance and video quality of digital cameras.
Application of new technology of digital camera
(A) progressive scanning technology
Traditional cameras use interlaced scanning, but in recent years, JVC and Panasonic are unique, and new camcorders adopt progressive scanning charge-coupled devices (such as JVC GR-DVL9600 and Panasonic MV-DS44EN), which makes the captured images clearer and more layered.
At first, due to technical reasons, we had to use interlaced scanning to reduce the bandwidth, that is, an image was artificially divided into two fields, odd lines and even lines, and then these two occasions were made into a frame image on TV. Because of the visual difference when scanning odd lines and even lines respectively, the image becomes blurred. The camera should use progressive scanning CCD to ensure higher image quality during playback (especially when playing back still images). Because there are no odd lines and even lines in the picture, it can be guaranteed that the dynamic and static pictures are as clear as before. This is especially suitable for converting images into computer image format or printing by printer. After the camera adopts progressive scanning, the image quality can be comparable to that of a digital camera. In addition, the progressive scanning camera can shoot at twice the shooting frequency of traditional cameras, especially sports shooting, and can clearly capture the smallest motion changes.
(B) special replay new technology
Pocket digital cameras are often designed with special playback functions, mainly occupying still images (pause/still), slow playback (slow playback) and fast playback (fast playback). And quick search. The special playback function is realized by multi-head mode and dynamic tracking mode. The so-called multi-head mode is to add a head specially used for special playback in addition to the original two video heads, and provide 3~8 heads according to different functions. The so-called dynamic tracking is to ensure that there is no noise in special playback, and an automatic scanning tracking system must be established. This system can detect the direction and angle of the playback track deviating from the track, and then correct the error of the playback track through the closed-loop electronic servo circuit, so as to achieve the purpose of tracking the track correctly. That's why dynamic tracking is needed. Because if dynamic tracking is not used, because of the use of multiple special playback heads, for example, when playing at high speed, the heads have to track and scan several tracks, and noise bands will inevitably occur whenever they pass through tracks with different azimuth angles. Dynamic tracking technology is used to control the movement of the magnetic head at any time, so that the tracks with the same scanning azimuth can be completely tracked, thus eliminating the noise band.
(3) New technology of recording media
For a long time, camcorders used magnetic tape as the only recording medium. With the development of digital compression technology and hard disk storage technology, this dominant situation began to be broken, and digital storage media such as magnetic disk, magneto-optical disk, computer memory card and hard disk all found their own positions in the camera.
First of all, the MD hard disk camcorder of Ikebana Company in Japan broke this pattern. This machine is equipped with two 2.5-inch hard disks, and the image compression mode is JPEG, which can record 20 minutes of Betacam-level material. Its biggest feature is that it has an image 10-60 seconds in advance, so even if the recording start button is set after the scene you want to record appears, the lens will not be lost. Secondly, it also has a simple editing function. After the shooting is completed, it can be nonlinear edited by a single machine, which ensures the rapid and timely production of the program. 1999, Sony also introduced the first digital camera with MD as the storage medium-Sony, DCM-M 1, as shown in Figure 3-82. It can shoot not only dynamic images, but also static images.
FD stands for floppy disk, a digital video camera with 3.5-inch floppy disk as auxiliary recording medium.
Hewlett-Packard and Sony jointly developed a digital video camera with magneto-optical disc as the recording carrier, which was launched in 2000. The CD can record images for 30 minutes at a coding speed of 5 megabits per second. In addition, Sony also introduced the DV-format camcorder ——trv 9000 with PCMCTA card as the record carrier for the first time, and the camcorder TRV17 with memory stick. , which further expands the video recording.
TRV-9000 with PCMCTA card as record carrier
(D) New technology of detail correction
Detail correction is one of the biggest factors that affect image quality. Digital cameras have introduced a series of new technologies to control this important function. These new technologies mainly include the following contents:
Variable pulse width technology for horizontal detail signal
The optimal pulse width of the horizontal detail signal is influenced by the scene content, the bandwidth of the video recorder and other devices connected to the camera. High-performance digital cameras have the ability to adjust the frequency center when performing detail correction. The horizontal detail correction signal is composed of three detail signals with different frequency characteristics. These three signals are obtained by three digital filters. The purpose of changing the peak frequency of the synthesized horizontal detail signal is to change the mixing ratio of these three signals. When the peak frequency changes, the width of the detail correction signal or the effect of the detail correction signal will be improved appropriately.
Precise clipping technology of excessive detail signal
In high contrast images, such as the huge transition from dark to bright or from bright to dark, the camera may produce too much detail correction, thus producing "black halo" and "step tilt" effects; Around a very bright object, "black halo" looks like a dark black stool, while "step tilt" looks like a serrated hypotenuse. These effects are annoying. By using accurate cropping technology, digital cameras can cut off too many detailed signals in both horizontal and vertical directions, thus effectively reducing the influence of "black halo" and "step tilt".
Accurate skin color detail correction technology
Detail correction emphasizes the freshness and sharpness of the image, but in some shooting occasions, such as faces, soft images are needed. The function of skin color detail correction is to reduce the detail level of the area containing skin color in the image without reducing the detail level of other areas, so it can give a very natural skin color reproduction without affecting the clear edge images of other areas.
4. Dynamic Contrast Control (DCC) technology
Dynamic contrast control (DCC) can compress the brightness signals of high-brightness and high-contrast images, and can clearly reproduce the detailed signals of high-brightness areas. This processing can achieve a brightness dynamic range of 600%.
(5) Application of other new technologies
1. Line-by-line complementary color filtering technology
Using line-by-line complementary color filtering technology, such as JVC, can obviously improve the vertical resolution of the camera.
GR-DVL9600 is the first CCD progressive scanning digital camera, which adopts the company's unique progressive complementary color filter and can provide vertical resolution up to 560 lines. If compared with the traditional interlaced CCD camera, it is equivalent to the image quality of a camera with nearly one million pixels.
2. Broadband processing technology
Using broadband processing technology can obviously improve the horizontal resolution of the camera. In the traditional color camera, the traditional Y/C frequency separation mode is used to process luminance and chrominance signals. JVC Company broke this traditional mode in its progressive scanning camera GR-DVL9600, and adopted broadband processing technology to make the brightness signal slowly decrease, thus greatly improving the horizontal definition of the image.
3. Intelligent automatic switch technology
Digital video camera with intelligent automatic switch technology, as soon as the display screen (electronic viewfinder) is turned on, the power supply and lens will automatically turn on, and the camera will shoot as soon as it is turned on. This function is very useful for shooting video with firearms.