COMP 776 Spring 2009
Assignment 4: Stereo Matching
Due date: March 31, 5PM
The goal of the assignment is to implement a simple windowbased stereo matching algorithm
for rectified stereo pairs. You will be using the following stereo pair:
first image, second image
Follow the basic outline given in this lecture: pick a window around
each pixel in the first (reference) image, and then search the corresponding scanline in the second
image for a matching window. The output should be a disparity map with respect to the first view
(use this ground truth map for qualitative reference).
You should experiment with the following settings and parameters:
 Search window size: show disparity maps for several window sizes and discuss which window
size works the best (or what are the tradeoffs between using different window sizes). How does the running
time depend on window size?
 Disparity range: what is the range of the scanline in the second image that should
be traversed in order to find a match for a given location in the first image? Examine the stereo
pair to determine what is the maximum disparity value that makes sense, where to start the search
on the scanline, and which direction to search in. Report which settings you ended up using.
 Matching function: try sum of squared differences (SSD) and normalized correlation.
Discuss in your report whether there is any difference between using these two functions, both
in terms of quality of the results and in terms of running time.
In addition to showing your results and discussing implementation parameters, discuss the shortcomings
of your algorithm. Where do the estimated disparity maps look good, and where do they look bad? What would be required
to produce better results? Also discuss the running time of your approach and what might be needed to make
stereo run faster.
Extensions
You should also implement at least one of the following extensions. Of course, feel free to do
more than one for bonus points.

Convert your disparity map to a depth map and attempt to visualize the depth map in 3D. Just pretend that
all projection rays are parallel, and try to "guess" the depth scaling constant. Experiment with
displaying a 3D point cloud, or computing a Delaunay triangulation of that point cloud.

Find additional rectified stereo pairs on the Web and show the results of your algorithm on these pairs.

Find nonrectified stereo pairs and rectification code on the Web and apply your algorithm to this data.

Implement multiplebaseline stereo as described in this lecture (see
paper by Okutomi and Kanade). Use
this data.

Try to incorporate nonlocal constraints (smoothness, uniqueness, ordering) into your algorithm.
You can come up with simple heuristic ways of incorporating these constraints, or try to
implement some of the more advanced methods discussed in the course (dynamic programming, graph cuts).
For this part, it is also fine to find code on the web.

Got another idea not listed above? Just send me email and I'll let you know whether it's OK for the assignment.
Turning in the Assignment
As usual, please email me or post on the Web (1) your MATLAB code and (2) a PDF report file
that includes all your results and discussion by 5PM, Tuesday,
March 31.
