Project 1: Hybrid Image

Algorithm Design

The project implements laplacian pyramid to create hybrid images. The lower levels of the pyramid (which contain high frequency information) are taken from image A and the high levels of the pyramid(which contain low frequency information) are taken from image B, so that after reconstruction, when people go close up, A is perceived and when they go far away, B is perceived.

To create levels of laplacian pyramid, a 5-by-5 gaussian kernel is first used to blur the original image, and the laplacian image is derived by substracting the blurred image from the original one. Then down sampling the blurred image by picking up every other pixel before next iteration. To reconstruct the image, sum up all the laplacian images including the last level of gaussian pyramid. Before addition, high level pyramid images are first super sampled. In the super sampling process, a gaussian kernel (the same as the one in creating pyramid) is used to blur the image.

Discussion and Extra Points

Perceptual grouping is important when choosing image pairs. The objects in image pairs should be spatially well aligned. Of the pairs I choose, the sizes and the poses of the objects are almost the same, like the wolf and the lion. So when you are perceiving the lion, you can hardly notice the wolf, and vice versa.

The Matlab function imresize() is not used because the inside filtering kernel is unknown. In the process of creating pyramid and the process of reconstruction, the same gaussian kernel should be used. If imresize() is used in one of the processes, the results will be worse.

I've used color to enhance the effect. And in my opinion, color makes better effect for high-frequency components. Because with color, we'll have a stronger perception of texture details such as the hair on the lion, cat and the letters on the ring. And the low frequency components are more like the background.

Results

Best results are achieved at the indicated pyramid level and cutoff-frequency.

Orignial	Hybrid Color	Hybrid Gray

Lion and Wolf
pyramid_level = 8, cutoff = 3

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Orignial	Hybrid Color	Hybrid Gray

Pigsy and Monalisa
pyramid_level = 7, cutoff = 3

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Orignial	Hybrid Color	Hybrid Gray

Ring and Saturn
pyramid_level = 7, cutoff = 3

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Orignial	Hybrid Color	Hybrid Gray

Cat and Dog
pyramid_level = 7, cutoff = 3

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Orignial	Hybrid Color	Hybrid Gray

Einstein and Marilyn
pyramid_level = 6, cutoff = 2

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Orignial	Hybrid Color	Hybrid Gray

Car and Rhino
pyramid_level = 6, cutoff = 2

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