“Passing Period”

Peter Davis
CSE 455 — Computer Vision
Project 1 Artifact
(Scroll to final result)

Original Images

For this project, I wanted to use intelligent scissors to remove objects, not add them, to an image. My first idea was to magically remove all the dirty dishes from my sink.

However getting an image of a clean sink to replace the dirty one would have required, um, cleaning, so that was out of the question.

Instead, I used my camera's "panerama" mode to take several dozen pictures of people walking in front of Mary Gates Hall, without moving the camera, each photo with the same exposure settings. I wanted to remove the people from the sidewalk, so I used my intelligent scissors program to create a mask. (Actually, I chopped up the image into smaller chunks and reassembled them into one big mask, since iScissors choked on my multi-megapixel original.)

Chances were, I could find blank areas in the other images to cover every person. Using multiple images makes a much cleaner result than Photoshop's "clone" tool could.

I opened the original image and the mask in Photoshop.
I imported each of my other images as a layer on top of the original.
I made a copy of the mask, and expanded and feathered it by 3 pixels to avoid leaving artifacts at the edges of where the people used to be.
I applied the mask to each of the other images, and searched for a subset of them that could be combined to completely cover all of the people with an empty background. This was more difficult than it sounds, since the sidewalk was pretty busy and some people were moving very slowly, especially in the upper-right-hand corner. These are the ones I ended up using:
I realigned some of the images slightly to compensate for small movements of the camera between shots.
It might have been faster to manually assemble a clean background, but instead, using the "people mask" left behind nice shadows and reflections on the cement (well, nice for what I planned on doing with them). This was the result.

Final Image

Finally, I made a copy of the original image and applied the mask to get an image of only the people. I blurred this (Gaussian, 10 pixel radius), and reduced the opacity to about 80%. Then I layered it on top of the blank background.

Click the image for more detail; notice the sharp backgrounds seen through the ghosts.