New 35mm Cmos Image Sensor for Digital Cine Motion Imaging

Large format single-sensor digital cine cameras have emerged as an important worldwide creative choice for motion picture film origination. Most of these image sensors are based upon the established Bayer color filter array for encoding of the color components. Important advances in demosaicking algorithms have steadily improved the reconstruction of RGB video components that support the color correction and image manipulation required in postproduction. Canon explored an alternative to such reconstructive algorithms in a quest to pursue an overall image quality that aspires to achieve the superb aesthetics long associated with 35mm motion picture film. This paper will discuss an important new CMOS image sensor that requires no demosaicing algorithm and facilitates structuring of equiband 4:4:4 RGB video components directly from the image sensor. 1.0 Introduction In 2003 the first large-format single-sensor digital camera appeared accompanied by the message that it had been specifically developed to offer a digital alternative to motion picture film origination. In the decade that has followed, a broadening range of such cameras and camcorders has emerged from most of the global professional camera manufacturers. Even more remarkable has been the appearance of totally new manufacturers dedicated to the development of high-performance large-format digital acquisition systems. To the cinematographer, the most significant attraction of these digital acquisition systems is their ability to use the existing global inventory of 35mm motion picture film lenses. At the same time, new lenses – especially zoom lenses – are now being developed by all of the major optical manufacturers. Of special note – and a testament to the vigor of the competition in this arena of motion imaging – has been the rapidity with which a hierarchy of such cameras (in terms of cost, imaging performance, and operational features) has expanded. These cameras employ both CCD and CMOS imagers. While most of these single-sensor cameras have employed the Color Filter array (CFA) according to the popular Bayer [1] pattern, one notable exception chose to deploy an alternative RGB stripe filter system. 2.0 Goals of the New Image Sensor The unanticipated use of the new generation of hybrid HD DSLR cameras for both low-budget moviemaking, and even for inserts into quite high-end movie productions, spawned a considerable commentary on the merits and demerits of the motion imaging aspects of these cameras. A broad industry debate continues on this topic. Always, the imaging yardstick remains that of 35mm motion picture film. A great deal has been published over the past decade on the relative image performance of 35mm film and the various digital counterparts that have flourished in this period. Canon believes that a dedicated development to seek a highperformance image sensor specifically for digital motion imaging could capitalize on new sensor technologies to close the gap between film and digital imaging. 1 Specifically, it was believed that an image sensor could be developed that would aspire to address the multiple imaging attributes that collectively contribute to the superb overall image quality of a motion picture originated on 35mm film negative and projected from a positive print derived from that negative master (either by traditional photochemical processes or via a digital intermediate workflow). The first decision in the design of this new CMOS imager was to base its image size upon that of the well-known and standardized 3-perf 35mm motion picture film format – this decision anticipating the possibility of using the large global inventory of related film lenses. Figure 1 Showing in yellow the active image size of the new Canon image sensor compared to contemporary digital large format image sizes 3.0 Criteria for Origination of Cinematic Imagery The multi-dimensional aspects of image quality originated by motion picture film are well known to the cinematographer and have been amply published in the technical literature over many decades. They can be separated into the following imaging attributes: • Speed [2] Film sensitivity specified by Exposure Index (EI) • Picture Sharpness [3] [4] Objectively assessed from film system MTF • Granularity [5] Artifact due to non-uniformity of photographic deposit • Tonal Reproduction [6] Management of scene brightness ratios • Exposure Latitude [7] The full recording range of the film negative stock • Color Reproduction [3] [7] Spectral sensitivity of the three emulsions