![]() At a typical readout rate of 1 MHz, the read noise for this CCD is about 10 electrons/pixel, which yields a dynamic range of 44,900/10 or 4,490. Thus, a CCD with 6.7 x 6.7 micron photodiodes should have a maximum charge storage capacity (a full-well capacity) of about 44,900 electrons (or holes). In a high-performance cooled CCD camera, the well capacity is proportional to the size of the individual photodiode, such that the maximum number of electrons stored is about 1000 times the cross sectional area of each photodiode. ![]() Where N(sat) is the linear full well capacity stated as the number of electrons and N(noise) is the total value of the read and dark noise, also expressed as the number of electrons. The dynamic range is expressed in decibel units according to the following equation : Read noise is usually specified in the performance data sheets that accompany a CCD sensor, with typical values ranging from 10-20 electrons/pixel in high quality chips operated at room temperature, and dropping to 2-5 electrons/pixel in Peltier-cooled CCDs for scientific imaging applications. This includes noise from input clocking and fixed pattern, along with reset transistor noise and amplifier output noise. Read noise is a combination of all noise generated during readout of the device. Typical diode sizes in modern CCDs utilized in photomicrography range from 4.5 to 24 microns with corresponding well capacities of 20,000 to 600,000 electrons. Photodiode size determines, in part, the size of the depletion wells-larger diodes having greater full-well capacity compared to camera noise. The interscene dynamic range represents the spectrum of intensities that can be accommodated when detector gain, integration time, lens aperture, and other variables are adjusted for differing fields of view. ![]() As the dynamic range of a device is increased, the ability to quantitatively measure the dimmest intensities in an image (intrascene performance) is improved. The dynamic range of a charge-coupled device ( CCD) or complementary metal oxide semiconductor ( CMOS) image sensor is typically specified as the maximum achievable signal divided by the camera noise, where the signal strength is determined by the full-well capacity, and noise is the sum of dark and read noises. Concepts in Digital Imaging Technology Dynamic Range ![]()
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