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CS223B Homework 3 Wiki

• Do images have to be contained in the writeup? This makes the document somewhat unwieldy and seems to add little value.

We would like to see all the images, either embedded in the writeup or attached at your submission e-mail.

• When proving that C has nonnegative eigenvalues, can we invoke the property that positive semi-definite matrices have nonnegative eigenvalues? After you proved that C is positive semi-definite, it only takes one line to show that positive semi-definite matrices must have nonnegative eigenvalues anyway.

Yes. Definitely you can use the property.

• Helpful Hint -> When coding the Matlab portion of the homework, depending on how you set up your patch (i.e. template) be mindful of data types (double vs. uint8). If the patches are cast as uint8, when you take the difference between them any negative values are truncated to zero which is not correct...

• Can you explain what is wanted for "scaling factor for lighting invariance" in the Submitting section? Each feature vector for every image will have a different scale factor, and I'm not sure how to meaningfully display those numbers.

Please include the derivation of the scaling factor. We are not looking for a numerical value, because, as you said, it change for every keypoint.

• Is it ok to use 15x15 windows instead of 16x16? It's a little awkward to have the window size be even given that you can't put the feature point in the center of the window.

You can use 15x15 windows if you want to. It should not make much difference.