Charge-Coupled Device (CCD) is an analog shift register, enabling analog signals (electric charges) to be transported through successive stages (capacitors) controlled by a clock signal. Charge coupled devices can be used as a form of memory or for delaying analog, sampled signals. They are most widely used for serializing parallel analog signals, namely in arrays of photoelectric light sensors. CCDs are used in digital photography and astronomy (particularly in photometry, sensors, medical fluoroscopy, optical and UV spectroscopy and high speed techniques such as lucky imaging). Digital color cameras generally use a Bayer mask over the CCD. Each square of four pixels has one filtered red, one blue, and two green (the human eye is more sensitive to green than either red or blue). The result of this is that luminance information is collected at every pixel, but the color resolution is lower than the luminance resolution.