Video Cameras
Video cameras are used in machine vision, quality monitoring, security, and remote monitoring for industrial and commercial operations. Consumer video cameras are not covered in this search form. Video cameras can operate in monochrome or color. Monochrome is black and white, or grayscale; the image is presented in black, white, and grayscale. The range of colors is generated with varying combinations of different discrete colors. One common technique is sensing the red, green, and blue components (RGB) and combining them to create a wide spectrum of colors. Multiple chip color is a method of capturing color in which multiple chips are each dedicated to capturing part of the color image, such as one color, and the results are combined to generate the full color image. They typically employ color separation devices such as beamsplitters rather than having integral filters on the sensors. Choices for imaging technologies for video cameras include CCD, CMOS, tube, and film. Charge Coupled Devices (CCD) use a light-sensitive material on a silicon chip to detect electrons excited by incoming light. CMOS image sensors operate at lower voltages than CCDs, reducing power consumption for portable applications. In a tube camera, the image is formed on a fluorescent screen. Image is exposed onto photosensitive film, which is then developed to be played or stored.
Important performance specifications to consider when searching for video cameras include horizontal resolution, maximum frame rate, shutter speed, sensitivity, and signal-to-noise ratio. Horizontal resolution is the maximum number of individual picture elements that can be distinguished in a single scanning line. It is most common to characterize horizontal video resolution corrected for the image aspect ratio, or specify the resolution in the largest circle than can fit in a rectangular image. Thus, for example a 640 x 480 image would be specified as 480 horizontal lines. Maximum frame rate is the number of frames that can be captured per unit time, typically frames per second. Shutter time is the time of exposure or light collection. Typically may be set across a wide range. Sensitivity refers to minimum scene illumination for good image quality. The standard unit for illuminance is lux, or lumens per square meter (lm/m2). Signal-to-Noise ratio is defined as the peak-to-peak camera signal output current to the RMS noise in the output current. This ratio represents how prevalent the noise component of a signal, and thus the image uncertainty, is in the total signal. Noise sources include sensor "dark current," electromagnetic interference, and any other spurious non-image signal elements. Higher SNR numbers represent less image degradation from noise.
Analog video formats used by video cameras include NTSC, PAL, SECAM, RS170, RS330, and CCIR. Digital output interfaces common to vision sensors include RS232, RS422, RS485, parallel interfaces, Ethernet, DeviceNet, ARCNET, PROFIBUS, CANbus, Foundation Fieldbus, IEEE 1394 (Firewire), Modem, SCSI, TTL, USB, and radio or wireless. Choices for bits or pixels include 8 bits, 10 bits, 12 bits, 14 bits, or 16 bits. Color outputs are typically RGB, Y PbPr, Y/C (S-video), or composite.
Other parameters to consider when specifying video cameras include specialty applications, performance features, physical features, lens mounting, shutter control, sensor specifications, dimensions, and operating environment parameters.
