What is a CCD imager?
On CCD cameras, a CCD (“charge-coupled device”) is a detector sensitive to light. When light (consisting of discrete photons) hits the detector surface of the CCD microchip, electrons are given off and stored in the detector elements,or pixels. A CCD microchip consists typically of thousands of pixels. When CCD cameras are pointed at a brighter area of the sky, a larger number of photons come in contact with the chip. More photons generate a larger number of electrons. Thus, a brighter portion of an image has a greater number of electrons stored in each pixel.