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Image Sensors: Myths and Mythology
by Peter Brown
Do people really know how image sensors work? They say they do, or think they do, but the problem is that there are many misconceptions as to what image sensors really do and how they operate. This month's cover story features an interview with Dr. Ben Wu, chairman and founder of IC Media.
Dr. Wu received his BSEE from National Taiwan University in 1982 and MSEE and Ph.D. degrees from University of Florida in 1985 and 1989, respectively. Dr. Wu has published more than 25 papers and holds more than 10 patents in the area of device/circuit/design.
How do image sensors work?
These devices react to light in a more or less intensive manner depending on how much light actually lands on the device. The photodiodes in the sensor are reset to a predefined voltage. Photons striking the photodiode induce electrons to flow inside the photodiodes, which creates a voltage difference (Vpd) that is converted by an analog-to-digital converter (ADC) into digital signals. The digital signals can now be manipulated to create an image that is processed for quality and display, the color patterns (R/G/G/B) are then grouped together to produce the final images with the best color representation.
Where does the image sensor fit in the overall camera?
The image sensor is physically installed between the lens (incoming light channeling component) and the digitizing circuit that will interpret and handle the image. In effect, it sits where the film used to be in non-digital cameras. In most cameras, an image sensor processor receives the signal from the image sensor to perform further image processing such as exposure time control, white balance, color correction and other tasks to enhance image quality.
Do image sensors from different manufacturers produce a different feelto the image being recorded, not unlike different film manufacturers producesofter or harsher results?