15-463 Assignment 2

By Jitu Das (cdas)

Overview

In this assignment, I took pairs of images and combined them to form a hybrid image. A hybrid image is created by taking the high frequency features of one image and adding them to the low frequency features of another image. The result has the property that when viewed from close or at large scale, the high frequency features are clearly visible and dominate the low frequency features of the other image. However, when viewed from afar or at a low scale, the high frequency features are too high to be seen (or displayed by the screen) and the low frequency features appear to be higher. So then the low frequency features are more visible than the high frequency features and the second image is dominant.

The process for producing the hybrid image is relatively simple. To get the low frequency features of one image, a low pass filter is applied by applying a gaussian blur. The spread of the gaussian blur is determined by the desired cut-off frequency, and the size of the filter generated by Matlab is three times the cut-off frequency. The high frequency features are extracted by applying a gaussian blur at a cut-off frequency to extract the opposite of what we wish to keep, and then the blurred image is subtracted from the image to retain only the high frequency componenets. Finally, the two images are added at the end, which is effectively the same as taking the average.

Results

Richard Stallman + Dennis Ritchie = Richard Ritchie

I think this hybrid image turned out the best out of the ones I tried. This is probably due to the fact that the two people have a similar physical appearance as they both have large beards. Stallman's hair is retained in the hybrid image since it is a high frequency feature, but the it very neatly disappears when the image is shrunk. The skin on both faces match well also. Also the background in the two images don't interfere with each other.

	Richard Stallman	Dennis Ritchie	Hybrid
Original			Low pass filter cut-off: 7 High pass filter cut-off: 15
Filtered
FFT

Banana Moon

These images work reasonably well, although the shading of the moon in the hybrid is not convincing. Both images have a similar shape so the hybrid retains this shape. The craters of the moon are high frequency features and these are also visible in the hybrid image and they disappear when the image is shrunken. The banana is composed of very low frequency features since there isn't much variation in color of the banana.

	Moon	Banana	Hybrid
Original			Low pass filter cut-off: 7 High pass filter cut-off: 15
Filtered
FFT

Heliplane

The helicopter-airplane combination didn't work nearly as well as I had hoped. I chose these two images since they both have similar backgrounds. However, the shape of the helicopter was too different from the shape of the airplane and the high frequency features of the helicopter don't disappear when the image is shrunken. Instead, the helicopter's high frequency features still dominate the airplane. This may be because the helicopter is darker and is adding contours to the smooth colored fuselage of the plane.

	Helicopter	Plane	Hybrid
Original			Low pass filter cut-off: 7 High pass filter cut-off: 15
Filtered
FFT