1. Main technical indicators of CCD color camera (1) CCD size, which is the camera target surface. In general, the larger the size, the more pixels it contains, the higher the resolution and the better the performance. Under the same number of pixels, the larger the size, the richer the image hierarchy displayed. (2) CCD pixels It is the main performance indicator of CCD, which determines the clarity of the displayed image. The higher the resolution, the better the image details. The CCD is composed of area array photosensitive elements, each of which is called a pixel. The more pixels, the clearer the image. Most of the market is currently delimited 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 cameras is between 320 and 500 TV lines, mainly 330 lines, 380 lines, 420 lines, 460 lines, 500 lines and Other different grades. The resolution is represented by a TV line (referred to as the line TV LINES), and the resolution of the color camera is between 330 and 500 lines. The resolution is related to the CCD and the lens, and is also directly related to the bandwidth of the camera circuit channel. The usual rule is that the bandwidth of 1 MHz corresponds to a resolution of 80 lines. The wider the band, the clearer the image and the larger the line value. The resolution is the number of horizontal lines multiplied by 0.75. Therefore the highest vertical resolution is: NTSC: 525 X 0.75 = 393; PAL: 625 X 0.75 = 470. Horizontal resolution measurement method: a. Inspection (analysis) diagram: Take the inspection chart directly from the camera and read the vertical and horizontal resolution directly on the monitor. When multiple cameras are being tested, the same lens should be used (recommended for fixed focus, two variable lenses), and the center circle of the test card appears on the left and right sides of the monitor screen, and the number of the given is clearly and accurately The tick marks a total of 10 sets of vertical lines and 10 sets of horizontal lines. Represents vertical and horizontal resolution, respectively, and gives the corresponding number of lines. Such as vertical 350 line level 800 line. At this point it is best to use a high-line black and white monitor. You can focus on the distant object during the test, or focus on the side. It is best to use both, and you can see the difference in this camera (convergence in the distance). b. Bandwidth measurement: Use an oscilloscope to measure the bandwidth of the camera to read the image signal. Measure the bandwidth and multiply by 80 to determine the resolution of the camera. For example, if the measured bandwidth is 5 MHZ, use 5 X 80 =400. (4) Illuminance Also known as sensitivity. F: LUX = 1:10 a. Minimum illumination. The minimum illumination is also an important parameter to measure the pros and cons of the camera. Sometimes the word "lowest" is omitted and it is directly referred to as "illuminance". The minimum illuminance is the brightness value of the scene when the brightness of the subject is low to a certain extent and the video signal level output by the camera is lowered to a certain value. The determination of this parameter is also related to the lens, and the maximum relative aperture of the lens should be specified. For example, when using the lens of F1.2, when the brightness value of the subject is as low as 0.04Lux, the amplitude of the video signal output by the camera is 50% of the maximum amplitude, that is, 350mV (the maximum amplitude of the standard video signal is 700). mV), the minimum illumination of this camera is 0.04 LUX / F1.2. The brightness value of the subject is lower, and the amplitude of the video signal output by the camera is less than 350 mV. It is reflected on the screen of the monitor, which is a gray image that is difficult to distinguish. It is the sensitivity of the CCD to ambient light, or the darkest light required for normal CCD imaging. The unit of illuminance is lux. The smaller the value, the less light is needed and the more sensitive the camera. In the minimum illumination measurement, the camera is placed in the darkroom. The front and rear of the darkroom are active 220V incandescent lamps, and the peripheral regulators can adjust the voltage from 0V to 250V. Adjust the brightness of the dark room light, the light can be adjusted from the brightest to the darkest. When the camera aperture is opened to the maximum during the test, the next minimum illuminance value is recorded (the active lamp is dimmed to the dark room). Built-in test chart) Then the aperture is minimized and the next minimum illuminance value is recorded. When the useful video signal amplitude (black level to white level) detected on the oscilloscope is reduced to 70 MV, the illuminance on the test chart is measured by the illuminometer. value. Cameras with a sensitivity of 0.1 lux or more are common type; cameras below 0.1 lux are highly sensitive, also known as electronic sensitized cameras or night vision cameras. The sensitivity of the camera is usually indicated by the minimum ambient illumination requirement. The sensitivity of the black and white camera is about 0.02-0.5 Lux (lux), and the color camera is more than 1 Lux. The 0.1Lux camera is used for normal surveillance applications; it is recommended to use a 0.02Lux camera for nighttime use or when ambient light is weak. When used with a near-infrared lamp, a low-light camera must also be used. b. Maximum illumination. When the highest illumination is measured, the camera is placed in the darkroom. The front and rear of the darkroom are active 220V incandescent lamps. The peripheral voltage regulator can adjust the voltage from 0V to 250V. Light can also be adjusted from the darkest to the brightest. During the test, the camera aperture is opened to the maximum measurement test chart, and the voltage of the voltage regulator is adjusted. When the amplitude of the video signal detected on the oscilloscope does not exceed 150% of the rated value, the illuminance value on the test chart is measured by the illuminometer. Record the highest illuminance value. (5) Scanning system. There are PAL and NTSC systems. (6) Signal to noise ratio. Signal to noise ratio is also a major parameter of the camera. The so-called "signal-to-noise ratio" refers to the ratio of the signal voltage to the noise voltage, and is usually expressed by the symbol S/N. S represents the image signal value of the camera when the meta-noise is assumed, and N represents the noise value (such as thermal noise) generated by the camera itself, and the ratio of the two is the signal-to-noise ratio, expressed in decibels (dB). The higher the signal to noise ratio, the better, typically 46 dB. Since the signal voltage is much higher than the noise voltage under normal conditions, the ratio is very large. Therefore, the actual calculation of the camera signal-to-noise ratio is usually based on the ratio of the mean square signal voltage to the mean square noise voltage. The number is multiplied by a factor of 20, expressed in dB. The typical value is 46db. If it is 50db, the image has a small amount of noise, but the image quality is good. If it is 60db, the image quality is excellent and no noise occurs. When the camera captures a brighter scene, the screen displayed by the monitor is usually brighter, and the observer is not easy to see the interference noise in the picture; when the camera takes a darker scene, the screen displayed by the monitor is dim, the observer is It is easy to see the snowflake interference noise in the picture. The strength of the interference noise (that is, the degree of influence of the interference noise on the picture) is directly related to the quality of the camera signal-to-noise ratio indicator. The higher the signal-to-noise ratio of the camera, the smaller the influence of the interference noise on the picture. The signal-to-noise ratio values ​​given by the general camera are all values ​​when the AGC (Automatic Gain Control) is turned off, because when the AGC is turned on, the small signal is boosted, so that the noise level is also increased accordingly. The typical value of the CCD camera signal-to-noise ratio is generally 42dB-56dB. When measuring the signal-to-noise ratio parameter, it should be directly connected to the video output terminal of the camera using a video clutter. The noise of the camera is related to the choice of gain. When in the gain boost position, the noise naturally increases. Conversely, in order to clearly see the effect of the noise, it is possible to observe in a state where the gain is increased. In the same state, different cameras are compared and compared to distinguish the advantages and disadvantages. The general camera's gain selector switch should be set to ON (0DB) for observation or measurement. The noise is also related to the contour correction (hook). Contour correction enhances the outline of the image while making the contour of the noise enhanced, and the particles of noise increase. The contour correction switch should normally be turned off during noise testing. The so-called contour correction is to enhance the detail components in the image. Make the image appear sharper and more transparent. If you remove the contour correction, the image will look awkward and blurry. Early contour correction was only performed in the horizontal direction. Nowadays, digital contour correction is used to correct both horizontal and vertical directions, so the effect is more perfect. However, the contour correction can only be achieved to an appropriate extent. If the contour correction amount is too large, the image will appear stiff. In addition, the result of the contour correction will make the face of the person's face become more prominent. The measurement uses a low-pass filter of 6MHZ and a 100MHZ high-pass filter. When testing, the camera aperture is opened to the maximum measurement test chart, and the AGC (automatic gain control) is turned off and the contour correction (hook) is turned off. When the amplitude of the video signal detected on the oscilloscope is 0.7Vp-p, the lens cover is covered, and the video signal measured on the video clutter measuring instrument should be about 0.4Vp-p. Then calculate the signal to noise ratio value. (7) Video output. The video signal output by the camera is composed of a luminance signal, a chrominance signal, a synchronization signal, a color burst signal, and a blanking signal. During the test, the camera aperture is opened to the maximum measurement test chart, but the image cannot be over-whitened and overloaded, and then the close-up image or test chart is adjusted by adjusting the focus. Use a waveform oscilloscope to measure its value. Mostly 1Vp-p to 1.2Vp-p 75Ω, both use BNC connectors. among them: A. Output luminance amplitude measurement. Keep the lens aperture as far as possible to the maximum, do not make the image too white and overload, and then adjust the focus to make the close-up image clear. Measure the value with a waveform oscilloscope B. Output synchronous amplitude measurement. Keep the lens aperture as far as possible to the maximum, do not make the image too white and overload, and then adjust the focus to make the close-up image clear. Measure the value with a waveform oscilloscope C. Output color burst amplitude measurement. Use a waveform oscilloscope to measure the duration of the burst signal, or read the number of cycles of the subcarrier. The output oscilloscope measures the output signal. R is measured. The amplitude and phase of the three colors YL and CY. When measuring the amplitude, the color synchronization amplitude is calculated as 100%. When the phase is measured, the color burst vectors are coincident. D. Output color subcarrier amplitude measurement. Cover the lens cover and measure the distance from the center of the bright cluster to the origin of the vector oscilloscope coordinate vector oscilloscope, and then convert it into voltage. e. Output blanking signal amplitude measurement. Keep the lens aperture as far as possible to the maximum, do not make the image too white and overload, and then adjust the focus to make the close-up image clear. Use a waveform oscilloscope to measure its value. (8) Color reduction test. Test this parameter should choose a good color monitor. First, observe the characters and costumes from a distance, see if there is any color distortion, compare the objects with bright colors, look at the sensitivity of the camera response, and put the color test chart in front of the camera to see the clarity of the picture, too light or too thick, and respond again. The moving colored objects are photographed to see if there is color tailing, delay, blurring, etc. (9) Backlight compensation. There are two ways to test this parameter: one is to open the front side of the camera in the dark room, adjust to the brightest, then place a picture or text below the light, the camera to the camera, see the image and Whether the text can be seen clearly, the picture is not glaring, and adjust the ON, OFF pull switch to see if there is any change, which effect is best. The other is to take the camera out of the window in the sun, and see if the image and text can be seen clearly. Ningbo Kyson Cool Electronic Technology Co., Ltd. , https://www.kysonrefrigeration.com
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