The dynamic range with CMOS is usually lower, especially with high gain and longer exposures.ĬMOS readout is faster because circuitry is simpler and usually 12-bits rather than 16-bits, and pixels cannot usually be binned before readout, as with a CCD to increase sensitivity and reduce noise. High dynamic range means that with a single exposure both low and high intensity features can be seen, by choosing the perceived intensity range of 256 levels out of a possible 65,536 (16-bit). CMOS technology is however developing rapidly, dark current has been reduced, and efficiency increased with back illuminated chipsīoth CCD and CMOS cameras can use Peltier cooling to reduce thermal noise, but because the total noise is lower for CCDs, and readout is 16-bits, the dynamic range is higher. Resolution in radiography is determined in practice by the resolution of the scintillator (50-100µm for ordinary 6LiF/ZnS), beam collimation and the distance between object and scintillator, while an optical camera is limited in principle only by the wavelength of light (~0.5µm).ĬMOS cameras have faster readout and lower readout noise, but at the expense of higher thermal electronic noise (dark current) which becomes important for the long (seconds or minutes) exposures often needed with neutrons. Light gathering capacity depends directly on pixel area, and this is more important than small differences in quantum efficiency. CMOS cameras have advantages, but also disadvantages.
Large pixel CCD and megapixel CMOS cameras for neutron imaging.Ĭamera makers often emphasise the advantages of megapixel CMOS cameras, which are by far the most popular and usually the most suitable for commercial applications of optical imaging they are also less expensive to make.
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