Security monitoring terminology interpretation (camera parameters)
2018-05-23 14:01:05
Focal length (f): The focal length is the distance between the lens and the photosensitive element. By changing the focal length of the lens, the magnification of the lens can be changed and the size of the captured image can be changed. When the object is far from the lens, we can use the following formula: Lens magnification, focal length/object distance. Increase the focal length of the lens, increase the magnification, can narrow the distance, the scope of the picture is small, the details of the vision can be seen more clearly; if the focal length of the lens is reduced, the magnification is reduced, the scope of the picture is enlarged, and See bigger scenes.
Field of view angle: In the actual project, we often use the horizontal field of view angle to reflect the shooting range of the screen. The larger the focal length f, the smaller the angle of view, and the smaller the range of the picture formed on the photosensitive element. Conversely, the smaller the focal length f, the larger the angle of view, and the larger the range of the picture formed on the photosensitive element.
Aperture: The aperture is mounted on the rear of the lens. The larger the aperture is opened, the greater the amount of light passing through the lens and the higher the resolution of the image. The smaller the aperture is opened, the smaller the amount of light passing through the lens, and the sharper the image. low. Usually expressed as F (light flux). F=focal length (f)/clear aperture. In the technical indicators of the camera, we can often see such parameters as 6mm/F1.4, which means that the focal length of the lens is 6mm, luminous flux is 1.4, then we can easily calculate the clear aperture of 4.29mm. In the case where the focal length f is the same, the smaller the F value and the larger the aperture, the greater the luminous flux reaching the CCD chip, and the better the lens.
Illumination: Illuminance is a unit that measures the camera's sensitivity and is expressed in Lux, which means that the camera can capture images under dim lighting conditions. The lower the value of Lux, indicates that the camera can take clear images under lower light conditions. We know that the nominal value of the video signal generated by the camera is 1v, and the standard value is 700mv. For example, if a lens with an aperture of F1.2 is used, the amplitude of the video signal output by the camera is the standard amplitude when the illuminance of the scene being shot is 0.02 Lux. The value of 700mv is 33%-50%. At this time, the minimum illumination of the camera is 0.02Lux/F1.2. The minimum illuminance of the test must pay attention to the aperture of the lens. The smaller the F-number and the larger the aperture, the lower the required illuminance. Different apertures have different minimum illumination values.
Sharpness: The resolution of the camera is represented by lines, which are divided into horizontal lines and vertical lines. In practical engineering applications, we often use the horizontal line as the evaluation index of camera sharpness. The more lines, the higher the sharpness. The resolution of commonly used black and white cameras is generally 450-600, while the resolution of color cameras is generally 330-480. The larger the value, the clearer the imaging. In a general monitoring situation, a camera with about 450 lines can satisfy the requirements. For medical and image processing and other special occasions, a 600-line camera can obtain clearer images.
Resolution: Image resolution simply refers to the number of points displayed in the vertical direction of the screen's horizontal and vertical directions. For example, 1024×728, where “1024†indicates the number of points displayed on the screen in the horizontal direction, and “768†indicates the number of points displayed in the vertical direction. The higher the resolution, the clearer the image. The higher the resolution, the clearer the display of the image.
Field of view angle: In the actual project, we often use the horizontal field of view angle to reflect the shooting range of the screen. The larger the focal length f, the smaller the angle of view, and the smaller the range of the picture formed on the photosensitive element. Conversely, the smaller the focal length f, the larger the angle of view, and the larger the range of the picture formed on the photosensitive element.
Aperture: The aperture is mounted on the rear of the lens. The larger the aperture is opened, the greater the amount of light passing through the lens and the higher the resolution of the image. The smaller the aperture is opened, the smaller the amount of light passing through the lens, and the sharper the image. low. Usually expressed as F (light flux). F=focal length (f)/clear aperture. In the technical indicators of the camera, we can often see such parameters as 6mm/F1.4, which means that the focal length of the lens is 6mm, luminous flux is 1.4, then we can easily calculate the clear aperture of 4.29mm. In the case where the focal length f is the same, the smaller the F value and the larger the aperture, the greater the luminous flux reaching the CCD chip, and the better the lens.
Illumination: Illuminance is a unit that measures the camera's sensitivity and is expressed in Lux, which means that the camera can capture images under dim lighting conditions. The lower the value of Lux, indicates that the camera can take clear images under lower light conditions. We know that the nominal value of the video signal generated by the camera is 1v, and the standard value is 700mv. For example, if a lens with an aperture of F1.2 is used, the amplitude of the video signal output by the camera is the standard amplitude when the illuminance of the scene being shot is 0.02 Lux. The value of 700mv is 33%-50%. At this time, the minimum illumination of the camera is 0.02Lux/F1.2. The minimum illuminance of the test must pay attention to the aperture of the lens. The smaller the F-number and the larger the aperture, the lower the required illuminance. Different apertures have different minimum illumination values.
Sharpness: The resolution of the camera is represented by lines, which are divided into horizontal lines and vertical lines. In practical engineering applications, we often use the horizontal line as the evaluation index of camera sharpness. The more lines, the higher the sharpness. The resolution of commonly used black and white cameras is generally 450-600, while the resolution of color cameras is generally 330-480. The larger the value, the clearer the imaging. In a general monitoring situation, a camera with about 450 lines can satisfy the requirements. For medical and image processing and other special occasions, a 600-line camera can obtain clearer images.
Resolution: Image resolution simply refers to the number of points displayed in the vertical direction of the screen's horizontal and vertical directions. For example, 1024×728, where “1024†indicates the number of points displayed on the screen in the horizontal direction, and “768†indicates the number of points displayed in the vertical direction. The higher the resolution, the clearer the image. The higher the resolution, the clearer the display of the image.