Capturing the image: DIGIC processing
It is not only the quality of the camera’s lens and sensor that determines the quality of the image produced. Much of the credit must also go to the on-board mini-computer that processes the data from the sensor. Canon has developed the DIGIC (Digital Imaging Core) chip for this purpose.
The DIGIC II image processor - a powerful computer in your camera.
The second-generation DIGIC II processor is used in many of the recent EOS digital models. It delivers excellent image quality, responsive camera performance, faster continuous shooting and extended battery life.
DIGIC II is able to handle the high-speed calculations needed to process huge volumes of data and provide exceptionally high image quality in real time. DIGIC II does not run as software, but as hardware built into the camera's circuitry. It consolidates the functions of a number of separate processing units to save time, space and power.
Most digital camera manufacturers face a trade-off between camera responsiveness and the amount of processing each image can receive. To overcome limitations with processor speed and capacity, manufacturers can install large and expensive buffers as a temporary store for unprocessed data, or compromise image quality by ‘dumbing down’ image processing, or both.
DIGIC II is designed to avoid these compromises. The processor is so fast it can read, process, compress and write JPEG image data back to the buffer between exposures.
White Balance
Apart from the speed with which it clears data from the camera's buffer, the benefits of DIGIC II are most obvious in the areas of white balance (WB) adjustment. DIGIC II’s additional processing power permits more accurate calculation of auto white balance by taking into account factors such as orientation and subject position.
While other manufacturers use systems that divide the scene into hundreds of segments for white balance assessment, the DIGIC II processor has the time and power to look at tens of thousands of segments to build a complex plan of how the scene is constructed. This allows the camera to distinguish between more than one type of light source in a single scene and to treat each area individually for optimum white balance.
Longer life
One of the benefits that has come about with the introduction of DIGIC II is extended battery life. As the processor is only operating for very short periods, it doesn’t use much power - DIGIC II is part of the reason that the EOS 5D, for example, is capable of taking 800 shots on just a single battery charge at 20 degrees C (based on the CIPA Standard and using the batteries and memory card format supplied with the camera).
DIGIC III
DIGIC II has been a major feature of Canon digital cameras since the EOS-1D Mark II in 2004. DIGIC III retains the basic concept of DIGIC II and improves upon it with higher performance and faster speed. To cope with the very large signal processing required by the EOS-1D Mark III’s 10.1 megapixels and top continuous shooting speed of 10 fps, dual DIGIC III image processors are incorporated for parallel signal processing. The CMOS sensor reads out to the dual DIGIC III image processors simultaneously in eight channels.
By having two processors handle the workload, image processing is approximately 1.5x faster; CompactFlash card access speed is 1.3x faster, and SD card access is 2x faster, compared to the EOS-1D Mark II N. The extra power of dual DIGIC III image processors has also allowed analog-to-digital conversion to improve from 12 to 14 bits per channel, meaning that tonal gradation for RAW images is divided into 16,384 separate levels per channel rather than 4,096. When saved as a 16-bit TIFF image, the image retains the full range of tones obtained with 14 bits. Also, JPEG images, at 8 bits per color, are generated from the 14-bit data. This substantially reduces tonal skipping, improving gradation and overall image quality.