I recently attended a course in Image Processing and in one lecture my teacher showed me an image of Marilyn Monroe depicted in a newspaper. My teacher then took the newspaper and walked towards the students. When he got close enough, the image changed into Albert Einstein! What the heck was going on there? – It was a so-called “Hybrid image”, in this post I will explain what happened.
The concept of Hybrid images was invented by people at MIT and Glasgow University. For more information and examples, see SIGGRAPH paper http://cvcl.mit.edu/publications/Talk_Hybrid_Siggraph06.pdf.
Miley vs. Einstein
The trick with hybrid images is to embed information into an image that depends on the viewing distance. All you need is a simple image editor with filtering abilities and the ability to use layers. To get the best hybrid images, look for images of famous, recognizable people who look “similar” in a sense. For instance, Miley Cyrus sticking out her tongue is very recognizable as is Albert Einstein and they both have had their tongue displayed in a silly fashion.
I digress, but at this point I believe Miley Cyrus is more famous because of her tongue and not because of… something she does. Nevermind, I can’t remember what she does, it will come back to me at the end of this post, I’m sure. Needless to say, the only thing in common between Miss Miley and Einstein is that they both have a tongue, but that’s fine, that’s all we need.
Another pairing I was very pleased with is Chaplin and Hitler who are totally polar opposites only sharing the famous toothbrush mustache. Too bad for the toothbrush mustache.
Chaplin vs. Hitler
Anyway, in order to create the hybrid image you have to first align the photos. This means: scale, resize and rotate the features that are similar in both photos. Then, use a low pass filter on the image you wish to be viewable from a distance, in this case with the Einstein/Miley, it’s miss Miley. Miley will be blurry and her features will only become discernible to our eyes at a distance. Zoom out as far as you wish the image to be seen, blur the image until you cannot see who it is and then push back on the slider until you see. This method is good because we want to have as much blur as possible when we view the image close up. The photo of Einstein, on the other hand, needs to be high-pass filtered. Einstein will therefore only be viewable close up. The high frequency details will be lost from a distance, because of the lack of resolution in our eyes. The amount of high pass filtering is up for grabs, you have to tweak the amount. The illustration shows how it may look.
The hybrid image is simply a fading between the two images. In my example above I use approximately 44% of Miley and rest Einstein.
When we have our hybrid image, we can print it out and go around and show it to people, it’s fun! To spare you the effort of printing the images, I have created a short video showing how different viewing distances affect the appearance of the two hybrid images. I have not altered the images in any way, this is what you will see if you print the images and view them from different distances, it’s very cool.
