Google Begins Blurring Faces In Street View

mytrip notes a News.com article reporting that Google has begun blurring faces in its Street View service, which has spawned privacy concerns since its introduction last year. Google has been working for a couple of years to advance the state of the art of face recognition. Quoting News.com: 'The technology uses a computer algorithm to scour Google's image database for faces, then blurs them, said John Hanke, director of Google Earth and Google Maps, in an interview at the Where 2.0 conference...' Google wrote about the program in their Lat/Long blog."

Comments

Re:Can you focus out-of-focus pictures

[pavon]

You can't add pixels that aren't there, and an out of focus picture is effectively a lower resolution. No, it isn't. Think about an unfocused camera - all the light is still hitting film/CCD, it is just spread out. So from an information theory point of view you haven't lost any data, you just put it into another form. If you consider what would be a single point of light, the energy in that point is spread out in a normal distribution (aka bell curve, aka gaussian). So the blurred image is just all these Gaussians functions overlayed on top of each other. Computer blurring algorithms do pretty much the same thing.

From a signal processing perspective, this is the same as convolving with a Gaussian. And if you take the Fourier transform of that blurred image, you get the transform of the image multiplied by the transform of the Gaussian (which is just another Gaussian). From there all you have to do is divide by this Gaussian, take the inverse transform, and walla, you have the desired non-blurred image. This is called a deconvolution, and I've written code to do this for an image processing class.

There are some caveats. You have to guess how blurred the image is - what focal length is and what not. Noise and compression can kill you, so you need to filter those out first (or limit your deconvolution filter to low frequency content). In addition at the edges of the image (or edge of the blur boundary) information is genuinely lost as the gaussian falls outside the boundary and is discarded.

Focus Magic is a commercial package that refocuses blurred images, and they have some interesting sample photos.