Canon® EOS 40D Digital Field Guide

Appendix A. Image Sensors and the Canon DIGIC Processor

In This Appendix

• Sensor technology

• DIGIC III image processor

As Canon's ongoing research and development continues to refine camera features, Canon has progressively applied new and improved technologies throughout its camera lineup. As a result, photographers can rely on a consistently high level of quality, and this is certainly true in the EOS 40D.

An understanding of both the sensor technology and the internal processor is beneficial to better understand the camera and the image files that it produces.

Sensor Technology

The 40D features a Canon-produced CMOS (Complementary Metal Oxide Semiconductor) image sensor. While Canon isn't the only camera manufacturer that uses CMOS sensors, it is the only company, at the time of this writing, that produces and markets full-frame, 35mm-size image sensors. Canon is also one of the few companies that designs and manufactures its sensors in-house for all of its digital SLRs.

Sensors, of course, lie at the heart of digital photography. Digital cameras use either CMOS or Charge-Coupled Device (CCD) image sensors. CCDs were the norm for early digital photography image sensors. CCDs offer low image noise, but they are inherently limited in the speed of processing and by greater power requirements as compared to CMOS image sensors. CCDs are comprised of a matrix of photodiodes that accumulate an electrical charge in direct proportion to the amount of light striking them. The photodiodes convert ...