How do I use the face recognition feature

What does the face recognition function actually do?

The camera does not know what the most important parts of the picture are and therefore what you want to have in focus. Traditionally, autofocus systems have simply selected the closest object near the center of the image and focused on it. This can easily fail with irrelevant foreground details.

Face detection assumes that if there are people in the picture, you will likely want to focus on their faces. By recognizing the position of faces, the autofocus system can be instructed more precisely.

For such a scheme to work, you need to be able to read the image data continuously and focus on any point in the image. This basically means that for face detection you need live view and contrast-detection AF. This is one of the reasons why the feature has been slow to become available on DSLRs. Contrast detection is still slower than phase detection, so it's not the primary method of focusing on DSLRs. Another factor is that DSLR users tend to have a little more control over the operation of the camera and prefer to manually select AF points.

The really interesting development is that the Canon 1DX has a metering sensor that is high enough resolution to detect faces, so face detection can be used in conjunction with phase detection AF.

jrista ♦

It should also be noted that 1D X face detection (and possibly face detection in another camera) isn't limited to human face detection. I've read some articles where people used the 1D X face recognition feature to recognize bird and animal faces as well, which is quite an intriguing feature.

Matt Grum

@jrista this is probably the result of a really simple face recognition scheme looking for a round shape with two eyes! But yeah, I can see that would still be an advantage for wildlife photographers.

jrista ♦

I'm not sure it's that simple as it seems to work in profile ... For deer, elk, even bears ... that wouldn't really be a "round" face.