CS194-26: Image Manipulation and Computational Photography

Project 6A: Image Warping and Mosaicing

1) Shoot and Digitize Pictures

Example 1

I took these pictures of Seattle from the top of the Space Needle this past summer. There is significant overlap between the pictures, and there are a lot of details that should be easy to align!

Example 2

I took these mountain pictures in Utah. The features of the mountain should provide good details to base correspondences off of.

Example 3

This, as you can tell, is the Golden Gate Bridge in San Francisco.

2) Recover Homographies

For this part of the project, we had to compute the homography between the two images. To do this, I chose corresponding points on each image, and then used Least-Squares to find the matrix that would most closely transform the points from image A into the corresponding points from image B.

3) Warp the Images

The next step for this project was using the homography to warp one image so that the corresponding points aligned. This was done by multiplying the pixels in one image by the homography matrix to get the resulting warped image.
To check that this process was working, I used the following photos (with clear square tiles) and warped the corners of the tiles to the corner of a square.

Example 1

For this example, I used the four corners of the blue mosaic square on the floor.

Example 2

For this example, I used the four corners of the tile behind my cat. As you can see, this warp had an unfortunate effect on my cat's head.

4) Blend Images into Mosaic

The next step for this project was blending the warped images into a panoramic. To accomplish this, I used the already calculated correspondences to determine how much to shift the warped image. Then, after the warped image was shifted, I used an alpha channel with linear feathering to blend the aligned images together, setting alpha to be one at the center of the image and decreasing until it reaches 0 at the edges of the images.

Example 1: Seattle, as seen from the top of the Space Needle

Example 2: Utah Mountains

Example 3: Golden Gate Bridge

I learned that creating mosaic panoramics is fun, and as usual, that small details can trip you up really easily!