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Breaking The Imaging Barrier

Sensor technology moves from film parody to film parity and beyond

Labels: CanonSonyARRIRED

Modern digital cinema cameras continue
to evolve at breathtaking speed. Light sensitivity, resolution and dynamic range have increased exponentially in just the past few years. While modern cameras are highly dependent on lens technology, processing, storage and the advanced electrical engineering that allows for innovative new features, at the center of this progress lies what's probably the single most important and significant part of a digital camera: the imaging sensor.

Just a few short years ago, who would have thought that Sony and RED would introduce 8K and 6K sensors in the F65 and EPIC cameras, respectively? Who would have thought that ARRI would have made the successful change from a premier maker of motion-picture film cameras to a premier maker of one of the most popular digital cinema camera systems, the ALEXA? Who could have envisioned that Canon's latest DSLR, the EOS 5D Mark III, would continue to represent an almost unheard-of cost-to-image-quality ratio with the $3,500 camera seeing seemingly constant use in television shows and feature films, as well as indie production?

While all of the new features and technology have driven camera technology forward, at its heart, it has been the advances in imaging technology that have served as the catalyst for this latest step. Let's take a look under the hood at the imaging technology that drives each of the four most popular digital cinema cameras on the market.

ARRI ALEXA
Introduced in March 2010, the ARRI ALEXA has quickly gained a solid foothold in the world of feature film and television work by its differentiation in the market as one of the first true digital cinema cameras (www.arridigital.com). The ALEXA is based on an ARRI-designed CMOS sensor, which offers a base sensitivity equivalent to 800 ASA, low noise and unsurpassed latitude that exceeds 13 stops.

Although the science behind the breakthrough performance of ALEXA's custom-designed CMOS sensor is complex, the use of large pixels and a Dual Gain Architecture (DGA) are its two main principles. By employing unusually large pixels, ALEXA's sensor exhibits high sensitivity, wide exposure latitude and low crosstalk. DGA simultaneously provides two separate read-out paths from each pixel with different amplification. The first path contains the regular, highly amplified signal. The second path contains a signal with lower amplification to capture the information that's clipped in the first path. Both paths feed into the camera's A/D converters, delivering a 14-bit image for each path. These images are then combined into a single, 16-bit, high-dynamic-range image. This method enhances low-light performance and prevents the highlights from being clipped, thereby significantly extending the dynamic range of the image.

ALEXA's sensor design provides 32 pairs of outputs. Each channel is divided into a high-amplification (gain) path (H) and a low-gain path (L), resulting in 64 channels arriving at the 14-bit A/D converters. In the final images, the shadow areas are reconstructed from the high-gain path and the highlights are reconstructed from the low-gain path for an image containing meaningful luminance information in all 16 bits.

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