HDC network camera tells you the camera parameters

The camera is the eye of the TV monitoring system. The selection of the camera not only affects the quality of the monitoring system, but also directly affects the technical specifications of the system to meet the requirements of CB50198-94 "Civil Closed-circuit Monitoring TV System Engineering Specification". The following describes the camera's technical specifications and test methods.
Classification of Cameras Cameras currently on the market can generally be distinguished in the following ways:
According to the color of the image: Colour, black and white (B/W), color automatically turn black and white (automatically converted according to the size of the ambient light);
According to the sensor points: CCD, CMOS;
According to the size of the sensor: 1, 2 / 3, 1/2, 1/3, 1/4;
According to the power supply points: DC 12V, AC 24V, DC / AC 24V, AC 220V;
According to the sensitivity (minimum illuminance): conventional (general) camera color 1 ~ 3lux (F1.2, F1.4), black and white 0.05 ~ 0.1lux (F1.2, F1.4); lower illumination camera color 0.5 ~1lux(F1.2), black and white 0.01~0.05lux(F1.2); low-light camera is black and white 0.005~0.01lux(F1.2); Starlight camera is black and white 0.0001~0.005lux(F1.2);
According to the synchronization mode: random synchronization (internal synchronization), external synchronization, power synchronization, VD2 (pulse) synchronization;
According to the lens interface points: C format, CS format.
The main technical specifications of the camera The current technical standards used in the camera measurement are two: one is the national standard GB12338-90 "black and white universal application television camera measurement method", and the other is the international standard IEC1146-1-1994 "color television camera (PAL/SECAM/ NTSC) Measurement Methods. The main technical indicators of the camera include:
Polarity is divided into positive polarity and negative polarity. In the positive polarity, the bright area level is higher than the dark area level and the sync head is negative level; in the negative polarity state, the bright area level is lower than the dark area level, and the sync head is a positive level.
The output amplitude refers to the signal peak-to-peak value from the highest white level to the top of the sync pulse at a 75Ω load (standard amplitude is 1Vp-p, where the video level is 0.7Vp-p and the sync head is 0.3Vp-p).
The minimum illuminance refers to the illuminance of the camera when the amplitude of the video signal at the output of the camera falls to “a certain stipulated value”, and the “standard value” of each standard is not the same as that of the factory. Please pay attention to the reader. In addition, the minimum illuminance of the test is affected by many factors, including:
The defined values ​​of the useful signal (black level to white level) vary from manufacturer to manufacturer, and cameras with the same minimum illuminance have significantly different effects due to different amplitude values. For the chooser, this is to compare against the same conditions;
The same camera in different apertures, the minimum illumination is not the same. The larger the aperture, the larger the aperture, the lower the illuminance (that is, the sensitivity will increase);
The minimum illumination is also affected by the color temperature of the light source, such as: GB12338-90 standard is 28560K, EIA standard is 31000K; minimum illumination is also related to reflectance (target reflection and background); minimum illumination is also AGC size, shutter status, etc. related.
Active pixels (pixels)
For CCD and CMOS cameras, the effective primitives and sharpness are directly related, and generally they are linear. Taking a black-and-white camera as an example, the pixel size is 752×582 (CCIR) and the horizontal resolution is 570 TVL. If the pixel size is 795×596, the horizontal resolution is generally 580 TVL. The camera circuit has a certain degree of improvement and reduction.
Resolution (clarity)
It refers to the ability to distinguish between black and white lines with the same width and width of a single line of black and white lines, and the maximum number of lines per frame height identified on a common test chart. Resolving power is divided into horizontal resolution (H) and vertical resolution (V); there are also central resolution and edge resolution.
The brightness discrimination level, also known as gray scale, is the brightness level that can be distinguished from the blackest to the whitest in a television image.
SNR is the ratio of the peak-to-peak amplitude of the useful signal amplitude in the video signal to the effective value of the random clutter, expressed in decibels (dB). The SNR is divided into unweighted SNR and weighted SNR. The weighted SNR refers to the addition of a 6 MHz low-pass filter and a 100 kHz high-pass filter between the camera output and the video clutter measurement instrument. In addition, there is a distinction between luminance signal-to-noise ratio and chroma signal-to-noise ratio.
The scanning frequency refers to the number of scanning electron beam repetitions per unit time, which is usually expressed in Hertz (Hz).
Synchronization is divided into external synchronization, internal synchronization (random synchronization), power synchronization, VD2 pulse synchronization. Generally better cameras will have external synchronization, internal synchronization, power synchronization, and even VD2 pulse synchronization (such as Panasonic products). In general, DC-powered cameras have internal synchronization (random synchronization). The advantages are simple, and the disadvantage is poor synchronization. Especially in systems with video switchers and video matrices, the image will jump and not appear during the switching process. Steady phenomenon.
The main technical indicators of the camera measurement methods The main technical indicators of the camera measurement methods, mainly "IEC1146-1-1994 standard" and "GB12338-90 standard." "IEC1146-1-1994 standard" measurement device includes: (1) test card: optional EIAJ-A NO.3 resolution card, or EIAJ-A NO.4 or NO.5 multi-function card. (2) Light source: 3100K, two side light (here is a reflection card). (3) Oscilloscope: sorting line oscilloscope, vector oscilloscope TEK1741, and video comprehensive tester TEK VM-700A. (4) Black and white monitor: A monitor with a horizontal resolution of 1000 lines and a screen-down function (refer to Figure 1).
Figure 1 "IEC1146-1-1994 standard" measuring device and "GB12338-90 standard" measuring basic device includes: (1) test card: sub-transmission television integrated test chart (GB6996.1), transmissive television linear test chart A Type (GB6996.2), Transmissive Television Integrated Test Pattern B (GB6996.3), Transmission Television Grayscale Test Pattern A (GB6996.12). (2) Light source: A type light source, color temperature 2856K. (3) TV test signal generator: TEK-111A. (4) Oscilloscope: TEK-1741A. (5) Monitor: Panasonic B/W ≥ 800 lines (refer to Figure 2).
Figure 2 GB12338-90 standard measurement device polarity measurement includes the polarity of the output amplitude measurement, both can be measured using an oscilloscope, the measurement should be terminated 75Ω load.
The minimum illuminance measurement should first have a light source with adjustable illuminance. The reflective test card is the incident light source, or the transmissive test card is a transmission light source for adjustment. It should be noted that outdoor illumination may be from 1 x 10-4-2.5 x 104lux, 1 x 10-4 means at night without light (star level), 2.5 x 104lux means under strong sunlight. Light meter can use Japan Minolta low light meter.
The effective picture elements (pixels) can be measured using the TER company's video integrated measuring instrument VM-700A, plus the accessories of the CCD camera. This not only can measure the effective picture element (pixel), but also can measure the number of defects of the CCD device (poor number of pixels).
The black-and-white camera for sharpness measurement can use the test equipment and method of the national standard “GB12338-90 standard”. It can ingest the test chart of GB6996.1 with a video camera and observe the maximum number of lines that can be resolved on the wedge of the center of the image on the monitor. The color camera can use the test equipment and method of the international standard "IEC1146-1-1994 Color Camera (PAL/SECAM/NTSC) Measurement Method".
Taking a color camera (330TVL with a nominal horizontal resolution) as an example, it has been proved by experiments that the requirement of the visual measurement method and the waveform measurement method is the highest. If the visual measurement method is 330TVL, the waveform measurement method is followed by 300TVL. This is because the human eye has a delay effect, which generates a certain error; use the waveform analyzer (select oscilloscope) as the line selection measurement, which can be moved from the high TVL to the low TVL, to the critical waveform stability setting, read the line The corresponding value of TVL is more scientific.
In addition, there are differences between black and white monitors and color monitors. If a black-and-white monitor (≥1000TVL) is used, the camera's horizontal resolution measures 330TVL. If a color monitor (≥500TVL) is used and the camera is horizontally deterministic, 300TVL is measured.
Luminance discrimination level measurement, also known as gray scale measurement method, refers to the camera ingesting the GB699.12 gray scale test card, and uses the visual method to measure the maximum distinguishable brightness level on the monitor. It should be noted that: (1) Other grayscale cards may also be used, typically more than ten cards. (2) The brightness and contrast knobs of the monitor can be adjusted to measure at the maximum resolution.
The signal-to-noise ratio measurement and measurement instrument can be selected from the TEK company video comprehensive tester VM-700A, or the German R/S company video noise tester.
GB12338-90 standard measurement method is the camera ingestion GB699.12R grayscale test chart, so that the video output signal amplitude of the camera is 0.7VP-P, cover the mirror cover, read the letter on the video clutter measuring instrument Miscellaneous. Attention should be paid to the automatic control (AGC) and correction circuit of the camera when testing, and the 6MHZ low-pass filter and 100KHZ high-pass filter must also be connected.
Half Video Amplitude Measurement When the camera is aimed at the grayscale card and the aperture is adjusted so that the video output level is 350mVp-p, the video clutter meter is accessed. At this point to disconnect the camera's AGC and correction circuit, and access 6MHZ low-pass filter and 100KHZ high-pass filter.
Note that the noise is different at white level (700mVp-p), medium white level (350mVp-p), and black level (0.0mVp-p). The TEK-VM700A can also measure the video noise spectrum.
The scanning frequency measurement can be measured with the TEK-VM700A video integrated tester or with an oscilloscope with a digital time scale. Generally, the camera (PAL) frame rate of the random synchronization (internal synchronization) has a large error between the frame frequency and the line frequency and 24Hz and 15625 Hz, and the cameras of the same type also have deviations from each other. The power-synchronized camera frame rate and line frequency are 25 Hz and 15625 Hz.
Concluding remarks In addition, a good camera power supply with the same frequency can adapt to any one of the three-phase power supply, its power synchronization phase adjustable can be greater than 270 °.
The camera also has a lot of performance, such as: geometric distortion, chroma distortion, white balance, correction and so on. This article only describes the most common and most important technical indicators and their tests for the reader's reference.