Business Wire: Canon announces a Dual Pixel CMOS AF, an autofocus technology for the EOS 70D Digital SLR camera. Dual Pixel CMOS AF, a phase-detection AF technology conducted directly on the image sensor plane, employs a CMOS sensor on which all of the effective pixels are able to perform both imaging and phase-detection AF simultaneously to achieve dramatically improved AF performance over prior EOS cameras during Live View and video shooting. Each individual pixel on the CMOS sensor incorporates two independent photodiodes which output signals that can be used for both imaging and the phase-detection AF. Compared with earlier generations of Canon’s image-plane phase-detection AF, Dual Pixel CMOS AF realizes shorter focusing times, outstanding tracking performance and smoother autofocusing during video shooting.
Compared with the EOS Rebel SL1, which employs Hybrid CMOS AF II, the EOS 70D Digital SLR camera (scheduled to go on sale in September 2013), which is the first camera to feature Dual Pixel CMOS AF, not only achieves AF speed that is approximately 30% faster but also delivers improved Movie Servo AF tracking for continuously smooth focusing during video shooting, even when filming quickly moving subjects.
Here is the description of how it works form the Cannon's technology page:
"Each pixel on the EOS 70D camera's sensor consists of two independent photodiodes that function both as imaging points and as individual phase-difference AF sensors. When the shutter button is pressed, parallax images on each photodiode of the pixel are detected, the amount of lens drive is calculated to correct the amount of shift in the AF points, and AF is achieved nearly instantaneously. During image capture, the same two photodiodes record the image and output as a single pixel. By placing approximately 40.3 million photodiodes on the camera's sensor, two per pixel, this caliber of AF is possible on approximately 80% of the image plane, vertically and horizontally. When the image or video clip is being captured, the CMOS sensor behaves as it always has with EOS SLR cameras, unimpeded by the dual photodiodes and recording each individual pixel with virtually no loss of detail or sharpness."
Update: Canon Singapore published Vimeo video on the Dual Pixel AF principle: