Low Light Cameras

Low light cameras are designed for low light applications. They contain sensors that are highly sensitive to light and reduce images to a series of lines. There are two basic types of low light cameras: monochrome and color. Monochrome devices present images in black and white or grayscale. Color devices present images in a range of colors. Several color output methods are available. Some low light cameras transmit red, green and blue (RGB) image components as separate signals over three separate wires. Other low light cameras transmit only two signals, luminance (Y) and color (C), over separate cables. Composite outputs encode or compress red, green and blue components before superimposing them on the luminance of a single signal. The RGB signals are decoded and reconstructed for image display, but the bandwidth limiting of the signal compression limits the subsequent color faithfulness.

Low light cameras use several image sensing technologies. Charge coupled devices (CCDs) are light-sensitive silicon chips that detect electrons excited by incoming light. Complementary metal oxide semiconductor (CMOS) image sensors operate at lower voltages than charged coupled devices (CCDs), reducing power consumption for portable applications. Analog and digital processing functions can be integrated readily onto a CMOS chip, reducing system package size and overall cost. Charge injection devices (CIDs) are photosensitive image sensors that are often implemented with large-scale integration technologies. CIDs can be randomly addressed, read non-destructively, and sub-scanned in a small region. Tube cameras use an electron beam to read the image in a raster scan pattern. The image is then converted to a voltage that is proportional to the intensity of the image light. Film cameras include a shutter or manual door that admits light to a photosensitive film.

Performance specifications for low light cameras include horizontal resolution, maximum frame rate, shutter speed, sensitivity, resolution and signal-to-noise ratio. Horizontal resolution is the maximum number of individual picture elements that can be distinguished in a single scanning line. Maximum frame rate is the number of frames that can be captured in a unit of time. Shutter speed, the time of exposure or light collection, is typically set across a wider range of parameters. Sensitivity, the minimum scene illumination required for good image quality, is measured in lux or lumens per square meter (lm/m²). Resolution represents the number of signal levels and is available in 8, 10, 12, 14, or 16 bits. Signal-to-noise ratio (SNR) is the peak-to-peak camera signal output current to the root mean square (RMS) noise in the output current. Noise sources include sensor “dark current”, electromagnetic interference (EMI), and other spurious non-image signal elements. Higher signal-to-noise ratios indicate less image degradation from noise.

Analog video formats for low light cameras include NTSC, PAL, SECAM, RS170, RS330, and CCIR. The National Television System Committee (NTSC) 525-line color television standard is used in North America and Japan. Phase alternate line (PAL) is a 625-line, 25-frame per second color television standard used in Europe. Sequential color and memory (SECAM) is a composite color transmission system in which two color-different signals are transmitted on separate lines. RS170 is the standard black and white video format used in the United States at 525 lines and 30 frames per second. RS330 is used with signals generated by closed-circuit television cameras scanned at 525 lines and 60 frames per second. The Electronics Industry Association (EIA) established both the RS170 and RS330 standards. Comité Consultatif International des Radio Communications (CCIR) or the International Radio Consultative Committee is another international organization that sets and governs video signal standards.

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Part Numbers for Low Light Cameras