Dual Pixel RAW is a Canon innovation utilising both photodiodes on the EOS 5D Mark IV’s 30.4 Megapixel Dual Pixel CMOS AF sensor.
The Dual Pixel sensor’s pixels have a dual photodiode construction. This sensor design means the sensor can receive an A and B signals from the subject and to detect any phase differences between the two signals, allowing them to attain focus as part of the Dual Pixel AF system. When capturing the image, the sensor obtains the picture info from the combined A and B image signals. This technology making both focusing and image shooting possible with the same sensor.
During Dual Pixel RAW shooting, a single RAW file saves two images into the file. One image consists of the A+B combined image data and the other only the A image data. This means the Dual Pixel RAW files contains both the normal image and also any parallax information, which can be measured and subject distance information extrapolated. As Dual Pixel RAW images contain two images they are therefore double the file size of normal RAW images.
Using the Dual Pixel RAW Optimizer in Digital Photo Professional software, users can make use of the Dual Pixel data recorded with the Dual Pixel RAW image for microadjustments of the position of maximum sharpness using the depth information contained within the file.
When an image isn’t quite sharp enough in a specific area, such as on a subject’s eyes for example, it’s possible to adjust the image and bring sharpness back to a desired area.
With Dual Pixel RAW it is possible to adjust the position of out of focus areas, or ‘bokeh’ to enhance composition, for example moving an out of focus object that is obscuring the subject.
Unlike lens flare, which can sometimes be used creatively in making an image appear low in contrast and atmospherically ‘hazy’, ghosting is not desirable and shows internal lens reflections. This can be controlled with Dual Pixel RAW and minimized with careful adjustment.