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April 2012 www.tvbeurope.com


TVBEurope 53 The Workflow


high-contrast imagery: we have demonstrated 20 stops in the lab. Although CCD imagers are


today’s standard for top-end broadcast production, they have reached the end of their lifecycle, with no new


technological developments planned. CMOS imagers are relatively new in broadcast applications but are proven after years in millions of consumer devices and many professional applications as well.


The performance


characteristics of CMOS today see picture quality in professional three-chip cameras that is as good as the best CCD, if not significantly better — and performance will continue to


improve. Those looking for broadcast cameras today should think carefully before buying CCD technology since it is at the end of its life. CMOS imaging is available today, and promises even more in the future.


‘In 2007, we developed our own CMOS imager, the Xensium. It contains 2.4 million photosites, for a full 1920x1080 pixel raster’


means less stress on the chips and ultimately longer life. Even the finest CCD cameras


are at risk of image defects through leaking or flashing pixels over time, which increases the maintenance burden. The lower operating temperature of the Xensium CMOS chip, thanks to its low internal clock speed, makes for fewer defects. Those that do appear tend to be less severe and can be masked using automatic correction. A related issue is highlight smearing. Those who remember early CCD cameras will remember a vertical line running the full picture height from any point light source from spotlights to reflective jewellery. While the latest designs of IT CCD have minimised the effect, it is still there. Typically, vertical smear is specified at around -135 dB. However, if you are forced to shut the exposure time down, ie, for capturing fast moving objects without excessive motion blur, it can be reduced to -100dB which is still visible. CMOS imagers, because of their construction, produce no smearing. Sensitivity of CMOS imagers is also better today, with the promise of really exciting possibilities to come. For 2000 lux at 3200˚K, a CCD camera will be the equivalent of f10 or f11, while the CMOS camera will be f9. At higher colour temperatures, most CCDs require optical filtering which reduces the sensitivity, while CMOS with its high dynamic range can correct for colour temperatures digitally, maintaining full sensitivity. Because each photosite on a CMOS imager has its own amplifier, there is the prospect of manipulating gain across the image, either to look deeper into shadows or to create very


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