The water in the first row goes into a special row of storage buckets, the water in each bucket in the second row goes into its neighbor bucket in the first row, and so on across the whole CCD. When the CCD is read out, the water in each row of buckets is emptied into the adjacent row. Picture each pixel on the CCD as a bucket with a certain amount of water in it. The analogy that is almost universally used to describe this process is the "bucket brigade" analogy. When the CCD is exposed to light for a length of time, an image of whatever is being observed-whether a distant galaxy or cars in a parking lot-forms on the CCD as an array of differing electric voltages.Īfter an image has been recorded on the CCD, the device can be "read out," meaning that the voltages are extracted from the CCD for storage on a computer. The voltage accumulated by each pixel during an exposure is directly proportional to the amount of light striking it. Regardless of the pixel or grid size, however, each pixel on the CCD has the ability to convert the light striking it into an electric signal. The scale and resolution of the image a camera is able to form on the CCD depends both on the pixel size and the grid size. The pixels are tiny some CCDs have pixels only 9 microns across, while others may have 27-micron pixels. Although many CCD pixel grids are square, this is not always the case scanners and photocopiers, for example, have a single line of pixels that passes over the picture or page of text being imaged. Small CCDs may have a grid of 256 x 256 pixels, while large CCDs may have 4,096 x 4,096 pixel grids. The CCD surface is a grid of pixels (pixel is a contraction for "picture element").
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