Signal processing and automatic camera control for digital still cameras equipped with a new type CCD

Abstract

Nowadays, digital still cameras are becoming as popular as conventional film cameras. As over 3 mega-pixel cameras become the main stream of digital still cameras, they are accepted from a point of view of pixel numbers. However, from a point of view of "scene toughness," digital still cameras need further improvement. Current digital cameras have difficulties reproducing high-contrast images containing both dark and bright areas, with shadows tending to lose details and whites washing out. In order to improve "scene toughness," we have developed a new concept camera system, which can capture wider dynamic range images. Applying miniaturization technology of CCD device, we developed the new structure CCD, the Super CCD SR. One photodiode of the new type CCD is divided into two parts, and each of the two photodiodes has a different size and a different sensitivity. When it outputs an image by optimally combining the images from a high sensitivity part and a low sensitivity part, it has wider dynamic range, that means the camera equipped with the new CCD has the advantage of getting wider dynamic range photographic images by one device and by one exposure. To make the best use of this CCD device, new technique in signal processing and new automatic camera control are important, then we have developed the automatic system that controls the camera corresponding to the scene variation. In this paper we discuss the concept of the signal processing and the automatic camera control for the camera equipped with the Super CCD SR. In the front-light condition the camera exposure and tone control are operated not to lose highlight details. In backlight containing both dark and bright areas, these are operated to reduce flat shadows of main subjects and washing out of highlights against strong sunlight in the background. The camera we developed is capable of obtaining wider dynamic range images and achieves richer and smoother tonality for better reproduction of fine detail, and gets over the above problem and improves "scene toughness."