I got an email this weekend forwarding a cool optical illusion.  I thought I’d share it here on my blog:

If you are near to this picture, Mr Angry is on the left and Mrs Calm is on the right. If you view it from a distance, they switch places!

For me, stepping away from my computer and looking at the image from about 8 feet away did the trick.  Your mileage may vary.

CREDITS This illusion was invented by Philippe G. Schyns and Aude Oliva of the University of Glasgow. It is featured on this web page: http://cvcl.mit.edu/gallery.htm , listed under ‘Dr Angry and Mr Smiles’. It is taken from Schyns and Oliva’s paper, “Dr Angry and Mr Smiles: when categorization flexibly modifies the perception of faces in rapid visual presentations, Nov 1998”. It is a copyright image and if they tell me to take it off this web page, I will.

I didn’t use to do this, but now when I receive these emails, I tend to go online to see if I can ferret out the source.   I did a Google search for “Mr. Angry Ms. Calm” and I found this very illusion was a Digg front page post… 2 years ago!    Digg was pretty young back then, as you can tell from the comments that people left on the post, debating whether it merited “front page status” or not.

The original post is located here, if you are interested.

Interestingly, it was also on Boing Boing at the same time, and the original image creators actually commented:

The illusion works by manipulating the spatial frequencies of the image.  The low spatial frequencies (the rough, fuzzy shape information of an image) from one image (e.g. Mr. Angy) are combined with the high spatial frequencies (the sharp edge information of an image) from a different image (e.g. Mrs. Calm).  When viewing this hybrid image at a close distance, our perceptual system is able to extract and process the high spatial frequencies and thus we see the image where the high spatial frequencies were taken from.  When viewing the hybrid image at a distance further away, our perceptual system can no longer extract the high spatial frequencies meaning we only see the low spatial frequency information, thus we see the other image.  You can also get a switch in the hybrid image by squinting.”

For me, this is an interesting commentary on the speed and distribution of “unique content” around the web.  It took two years for a front page Digg post to make it to my inbox.

It’s also a really cool special effect. 🙂