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Today, which is considered as the era of color photography, some people scoff at black and white photography; Some people think that black-and-white photography is an outdated form; Others regard black-and-white photography as low-level photography and so on. This view is incorrect.

Black-and-white photography abstracts the objective color world into a black-and-white picture, and expresses the colorful world through the change of hue between black, white and gray. Although it is not as beautiful and lifelike as color photography, it is often more subtle, meaningful and attractive than color photography in artistic creation, which can also promote the creativity of photographers. In the field of news photography, due to the quality, cost and timeliness of newsprint, black and white photography still dominates.

As two basic forms of photography, black-and-white photography and color photography will last as long as photography itself, because they have their own advantages and good uses.

The choice of black and white film is simpler than that of color film. The first thing to pay attention to is black and white films with different color sensitivity.

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● Full color film, color blind film and color separation film.

The Significance and Use of Full Color Movies

Color sense refers to the sensitivity of emulsion to various colors. A full-color film can respond sensitively to red, orange, yellow, green, cyan, blue and violet light in visible light, and reproduce scenes with different brightness of black, white and strong light, and its effect is close to the brightness feeling of human eyes for various colors of the scene. For example, red reappears in dark gray, yellow reappears in light gray and so on.

Full color film is the most widely used in black and white photography. The commonly used black-and-white film is full color, which is not only used to shoot various subjects such as scenery, people and still life, but also to remake color pictures and charts. Domestic full-color film is marked with "full-color film" on the box; There are usually "Pan" signs on the boxes of imported full-color films, such as "Ilford Pan F" and "Kodak plus-XPan".

Significance and use of color-blind movies

Color-blind films are only sensitive to violet light and blue light in visible light. It is insensitive to red, orange, yellow and green light, commonly known as "insensitive" to these colors. This means that the scenes of these colors are all ready-made black again. Therefore, color-blind films are not used for ordinary shooting, but for remaking black-and-white words, black-and-white line drawings and copying black-and-white slides. Therefore, color-blind movies are also called "remake" and "reproduction". Note that the remake of the color part requires full-color film, not color-blind film.

Significance and use of color separation

Color separation is also called "positive color". It is insensitive to red and orange light in visible light, but sensitive to yellow, green, cyan, blue and purple light. Color separation is mainly used in modern photography, such as printing plate making, remake of black and white charts and reproduction of darkroom stunts. Usually, shooting is basically unnecessary. Commonly used domestic color separators are OA, OB, OC, SO. Because almost all black-and-white photography uses full-color film, the choice of full-color, color blindness and color separation film is relatively simple, as long as you pay a little attention. In the choice of black and white film, film speed is also the main consideration.

High-speed movies and low-speed movies

Black and white film, like color film, has various film speeds, but there are fewer types of film speeds than color film. The film speed types of black and white full-color film are: ISO25, 32, 50, 100, 125, 400, 1250, 3200, etc. , of which ISO50, 100, (or 125) is commonly used.

Like color film, the speed of black and white film also brings a series of internal changes in photographic performance. On the premise of the same production process, the film speed is high-large tolerance, coarse particles, low resolution, low contrast, heavy fog and poor preservation; Low film speed-small tolerance, fine particles, high resolution, high contrast, low haze and good preservation.

The selection method of high-speed film and speed substitute film is the same as that of black-and-white film and color film. See the section "High-speed film and low-speed film" in the first section "Selection of color film" for details.

Among modern black-and-white movies, there is a new type of black-and-white movie worthy of attention. This is a black and white film based on dyes.

Low dye black and white film

Dyed black-and-white film is also called "non-silver salt black-and-white film" and "color black-and-white film". At present, there are two brands on the market, "Ilford XP 1-400" and "Vario XL", which came out one after another in the early 1980s.

Characteristics of dye-based black-and-white film

The main feature of dye-based black-and-white film is that it is imaged with dye, which breaks the traditional practice of imaging black-and-white film with silver salt. Therefore, its processing technology is different from the usual black-and-white film processing technology, and it adopts color film processing technology. The above two kinds of dye-based films can be developed by "C-4 1 process" (color development and bleaching for 5 minutes each, liquid temperature 38℃). Although the manufacturer also recommended a more suitable color development process: "Ilford XP 1-400" is two special developer and bleaching solution; "Akefa Vario XL" is a color development process of "Akefa 70" or "Akefa F".

Advantages of dye-based black and white film

The main advantages of dye-based black-and-white film are as follows.

The tabletting speed is fast and the particles are fine. This is usually the performance that black and white movies can't have both. Usually, the speed of black-and-white film is high, and the material must be thicker, which is determined by the characteristics of emulsion itself. The calibrated film speed of the above two dye-based black-and-white films is ISO400, but "Ilford XP 1" can be improved to ISO 1600, and "Vario XL" can be improved to ISO3200 for shooting, with no obvious increase in granularity.

Exposure latitude is huge. The contrast of the evolving landscape is still overexposed and underexposed, and the image quality has not decreased significantly within a large error range. The allowable film speed range of XP 1 is ISO 50 ~ 1600, and that of XL is ISO 150-3200. This is an advantage of great practical value.

At high magnification, the granularity and clarity of the image are obviously better than that of ordinary black and white film.

The price of dye-based black-and-white film is similar to that of high-quality black-and-white film in the world, but because of the color development process, the cost of developing film is higher than that of ordinary black-and-white film, which is also more troublesome.

2 camera knowledge Monday, July 23rd, 2007 at 09: 57 am1. camera

The camera part is generally installed on the site, including camera, lens, protective cover, bracket and electric pan/tilt. Its function is to photograph the monitoring area and convert it into an electrical signal.

There are two kinds of cameras: color cameras and black-and-white cameras. Generally, black-and-white cameras are more sensitive than color cameras and are more suitable for places with insufficient light. If the purpose is only to monitor the position and movement of the scene, you can use a black and white camera. If you want to distinguish the details of the subject, such as the color of clothes and scenery, it is better to use colored ones.

The specifications of the camera can be divided into 1/3 ",1/2", 2/3 "and so on. , installation methods are fixed and translation/tilt.

In closed-circuit monitoring system, camera is also called camera or CCD (Charge Coupled Device). Strictly speaking, a camera is a general term for cameras and lenses. In fact, most cameras and lenses are purchased separately. Users can calculate the focal length of the lens according to the size of the target object and the distance between the camera and the object, so the lens needed by each user depends on the actual situation. Don't think that there is a lens on the camera (head).

The main sensitive element of the camera is CCD, which has the characteristics of high sensitivity, small distortion, long life, anti-vibration, anti-magnetic field, small size and no afterimage. CCD is the abbreviation of charge coupled device, which can convert light into charge, store and transfer the charge, and also take out the stored charge to change the voltage, so it is an ideal camera element. It is a new device to replace the camera tube sensor.

The working principle of CCD is that the light reflected by the photographed object propagates to the lens and is focused on the CCD chip through the lens. CCD accumulates corresponding charges according to the intensity of light, and generates electrical signals representing pictures after periodic discharge. After filtering and amplification, the standard composite video signal is output through the output end of the camera. This standard video signal is the same as the video output of home video recorder, VCD player and home video camera, so it can also be recorded or connected to TV to watch.

1, selection and classification of CCD cameras

CCD chip, like human retina, is the core of the camera. At present, China has no manufacturing capacity. Most cameras on the market use chips produced by Japanese companies such as Sony, Sharp, Panasonic and LG. Now South Korea has the ability to produce them, but the quality will be slightly inferior. Due to the different grades produced in chip production and the different ways obtained by various manufacturers, the acquisition effect of CCD is also very different. When buying, you can take the following methods to detect: turn on the power supply, connect the video cable to the display, close the lens aperture, and see if there are bright spots when the image is completely black, and whether the snow on the screen is big or not. These are the simplest and most direct methods to detect CCD chips, and no other special instruments are needed. Then you can open the aperture and look at the still life. If it's a color camera, you'd better take a brightly colored object to see if the image on the display is color cast, distorted, smooth or gray. Good CCD can restore the color of the scene well and make the object look clear and natural; However, the image of defective products will have a color cast, and even if it faces a blank sheet of paper, the image will display blue or red. Due to the dust in the production workshop, there will be impurities on the target surface of individual CCD. In general, impurities will not affect the image, but in low light or micrography, fine dust will also cause adverse consequences. If it is used in this kind of work, it must be carefully selected.

1, through a color camera that images colors: It is suitable for distinguishing the details of the scene, such as distinguishing the colors of clothes or scenery. Black-and-white camera: suitable for areas with insufficient light and areas where lighting equipment cannot be installed at night. When only the position or motion of the scene is monitored, a black and white camera can be used.

2. According to the resolution sensitivity, the image pixels below 380,000 are classified into general types, especially the products with 250,000 pixels (565,438+02 * 492) and 400 line resolution are the most common. A high-resolution image with more than 380,000 pixels.

3. According to the size of CCD target surface, CCD chips have developed various sizes: most of the chips used at present are 1/3 "and 1/4". When choosing a camera, especially when the camera angle is strictly required, the size of the CCD target surface and the cooperation between CCD and lens will directly affect the size of the field of view angle and the clarity of the image. 1 inch-The target size is12.7mm * 9.6mm high,16mm diagonal. 2/3 inch-the target size is 8.8 mm * width * 6.6 mm height, and the diagonal is 1 1/2 inch-the target size is 6.4 mm * width * 4.8 mm height, and the diagonal is 8 mm. 1/3 inch-The target size is 4.8 mm * width * 3.6 mm height, and the diagonal is 6 mm.. 1/4 inch-The target size is 3.2 mm * width * 2.4 mm height and 4 mm diagonal.

4.PAL system is divided according to scanning system. NTSC China adopts PAL system (black and white CCIR), and the standard is 625 lines and 50 fields. Only medical or other professional fields use some non-standard systems. In addition, the Japanese version is NTSC, with 525 lines and 60 games (EIA black and white).

5. According to the power supply mode, it is divided into 1 10VAC(NTSC system mostly belongs to this category), 220VAC and 24VAC. 12VDC or 9VDC (miniature cameras mostly fall into this category).

6. Internal synchronization according to synchronization mode: use the synchronization signal generated by the synchronization signal generation circuit in the camera to complete the operation. External synchronization: The external synchronization signal generator is used to send the synchronization signal to the external synchronization input of the camera. Power synchronization (line lock): use the AC power of the camera to complete the vertical push synchronization. External VD synchronization: input VD synchronization pulse on the camera signal line to complete external VD synchronization. External synchronization of multiple cameras: the external synchronization of multiple cameras is fixed, so that each camera can work under the same conditions. Because the cameras are synchronized, even if one of the cameras switches to other scenes, the picture of the synchronized camera will not be distorted.

7, according to the degree of division, CCD is divided into:

The illumination required for normal operation of ordinary type is 1~3LUX.

The illumination required for normal operation of moonlight type is about 0. 1LUX.

The illumination required for normal operation of starlight type is below 0.0 1LUX.

The infrared type is illuminated by an infrared lamp and can be imaged without light.

8. According to appearance: organic plate type, pinhole type and hemispherical type.

Main technical indexes of CCD color camera

(1)CCD size, that is, the camera target surface. Originally 1/2 inch, now 1/3 inch has been popularized, and 1/4 inch and 1/5 inch have also been commercialized.

(2)CCD pixel is the main performance index of CCD, which determines the clarity of the displayed image. The higher the resolution, the better the image details. CCD consists of array photosensitive elements, and each element is called a pixel. The more pixels, the clearer the image. At present, most of the markets are demarcated by 250,000 and 380,000 pixels, and more than 380,000 pixels are high-definition cameras.

(3) Horizontal resolution. The typical resolution of color camera is between 320 and 500 TV lines, mainly including 330 lines, 380 lines, 420 lines, 460 lines and 500 lines. The resolution is expressed by TV lines, and the resolution of color camera is between 330-500 lines. Resolution is related to CCD and lens, and also directly related to the frequency band width of camera circuit channel. Usually, the bandwidth of 1MHz is equivalent to the resolution of 80 lines. The wider the frequency band, the clearer the image and the larger the line value.

(4) Minimum illumination, also known as sensitivity. It is the sensitivity of CCD to ambient light, or the darkest light that CCD needs for normal imaging. The unit of illumination is lux. The smaller the value, the less light is needed and the more sensitive the camera is. High-sensitivity cameras such as moonlight and starlight can work in very dark conditions, and the general illumination is 2~3lux. Now there are also ordinary cameras below 1lux.

(5) scanning system. There are PAL system and NTSC system.

(6) Camera power supply. Ac power supply is 220V, 1 10V, 24V, and DC power supply is 12V or 9V.

(7) Signal-to-noise ratio. The typical value is 46db. If it is 50db, the image is a little noisy, but the quality is good. If it is 60db, the picture quality is excellent and there is no noise.

(8) Video output. Most of them are 1Vp-p and 75 Ω, using BNC connectors.

(9) Installation method of lens. There are two modes, C and CS, the difference lies in the different photosensitive distance.

2. Adjustable function of 2.CCD color camera

Select (1) synchronization mode.

1. For a single camera, the main synchronization methods are as follows:

Internal synchronization-use the crystal oscillator circuit inside the camera to generate synchronization signals to complete the operation. External synchronization-the synchronization signal generated by the external synchronization signal generator is sent to the external synchronization input end of the camera to realize synchronization.

Power synchronization-also known as linear locking or line locking-is to use the AC power of the camera to complete vertical push synchronization, that is, the camera is synchronized with the zero line of the power supply.

B For a multi-camera system, it is hoped that all video input signals will be synchronized vertically, so that the picture will not be distorted when the camera output is changed. However, because the power supply of each camera in a multi-camera system may come from different phases of the three-phase power supply, or even the whole system is not synchronized with the AC power supply, the measures that can be taken at this time are as follows: send all the synchronization signals generated by the same external synchronization signal generator to the external synchronization input terminals of each camera to adjust synchronization. Adjust the "phase adjustment" potentiometer of each camera. Because the vertical synchronization of cameras is in phase with the rising edge of alternating current at the factory, each camera can have different phase shift by using phase delay circuit, so as to obtain appropriate vertical synchronization, and the phase adjustment range is 0~360 degrees.

(2) Automatic gain control All cameras have a video amplifier, which can amplify the CCD signal to a usable level. Its amplification is gain, which is equivalent to high sensitivity, which can make it sensitive in low light. However, in bright lighting environment, the amplifier will be overloaded, which will distort the video signal. Therefore, it is necessary to use the automatic gain control (AGC) circuit of the camera to detect the level of the video signal, and switch the AGC in time to make the camera work in a large illumination range, that is, the dynamic range, that is, to automatically increase the sensitivity of the camera under low illumination, so as to improve the intensity of the image signal and obtain a clear image.

(3) Background light compensation Usually, the AGC working point of the camera is determined by averaging the contents of the whole field of view. However, if the field of view contains a very bright background area and a very dark foreground object, the AGC working point determined at this time may not be suitable for the foreground object, and the background light compensation may improve the display state of the foreground object. When the background light compensation is turned on, the camera only averages a sub-area of the whole field of view to determine its AGC working point. At this time, if the foreground object is located in the sub-area, the visibility of the foreground object is expected to be improved.

(4) In the CCD camera, the electronic shutter is operated by optically controlling the charge accumulation time on the image surface. Electronic shutter controls the CCD accumulation time of the camera. When the electronic shutter is closed, the CCD accumulation time of NTSC camera is 1/60s. For PAL cameras, it is 1/50 seconds. When the electronic shutter of the camera is opened, the electronic shutter of the NTSC camera covers the range from 1/60 seconds to1/0000 seconds at 26 1 step; For PAL camera, its electronic shutter covers the range from 1/50 seconds to110000 seconds in steps of 31. When the speed of the electronic shutter is increased, the light focused on the CCD will decrease within the time allowed by each video field, which will reduce the sensitivity of the camera. However, higher shutter speed will have a "pause action" effect on observing moving images, which will greatly increase the dynamic resolution of the camera.

(5) White Balance White balance is only used for color cameras, and its purpose is to realize that the camera image can accurately reflect the scene conditions. There are two ways: manual white balance and automatic white balance.

First, automatic white balance

Continuous mode-At this time, the white balance setting will be constantly adjusted with the change of the color temperature of the scene, with the range of 2800-6000k K. This method is most suitable for situations where the color temperature of the scene is constantly changing during shooting, so that the color is natural, but when there is little or no white in the scene, continuous white balance cannot produce the best color effect. Button mode-first aim the camera at white targets such as white walls and white paper, and then turn the automatic mode switch from manual to the setting position, and keep it at this position for a few seconds or until the image appears white. After performing the white balance, turn the automatic mode switch back to the manual position to lock the white balance setting. At this time, the white balance setting will be kept in the camera memory until it is changed again, with the range of 2300 ~ 1000. Setting the white balance by buttons is the most accurate and reliable, which is suitable for most applications.

B, manual white balance

Turning on manual white balance will turn off automatic white balance. At this time, there are as many as 107 levels to adjust the red or blue state of the image, such as red increasing or decreasing by one level and blue increasing or decreasing by one level. In addition, some cameras have orders to fix the white balance at 3200K (incandescent lamp level) and 5500K (daylight level).

(6) Color Adjustment For most applications, it is not necessary to adjust the color of the camera. If it needs to be adjusted, it needs to be carefully adjusted so as not to affect other colors. The color adjustment methods are: red and yellow are increased, and then red is moved to magenta. Red-yellow decreases. At this time, move red to yellow. Blue and yellow increase, at this time, move the blue to cyan one step. Blue-yellow decreases, so move the blue one step to magenta at this time.

3. Digital regulation control method

The new camera adopts digital adjustment control to adjust the above optional parameters. At this time, it is not necessary to manually adjust the potentiometer, but to use the auxiliary control code, and store these adjustment parameters in the digital storage unit, which increases the stability and reliability.

Digital signal processor (DSP) camera is called by introducing some digital processing technology on the basis of analog system. This camera has the following advantages:

1, because of digital detection and digital operation technology, has intelligent background light compensation function. Conventional cameras require the subject to be placed in the center of the picture, occupying a large area, so as to have better background light compensation, otherwise too bright background light may reduce the transparency of the image center. The DSP camera divides a picture into 48 small processing areas, which can effectively detect the target, so that even small, thin or not in the central area of the picture can be clearly presented.

2. Due to the adoption of DSP technology, white balance can be tracked automatically, that is, "white" can be detected and tracked under any conditions, and the original color can be reproduced through digital operation and processing functions. The traditional camera averages all colors on the screen, so if colored objects occupy a large area on the screen, the color reproduction will be unbalanced, that is, the original color cannot be reproduced. The DSP camera divides a picture into 48 small processing areas, so it can effectively detect white. Even if there is only a small piece of white on the picture, the camera can track it and reproduce the original color. When shooting a grid-like object, image aliasing caused by camera color noise can be minimized. The difference between the C interface and the CS interface is that the distance from the contact surface between the lens and the camera to the focal plane of the lens (where the CCD photoelectric sensor of the camera should be located) is different. The C interface is 17.5 mm, and the CS interface is12.5 mm. C-lens and C-camera, CS-lens and CS-camera can be used together. Adding a 5mm C/CS adapter ring between the C lens and the CS camera can