Ex 2 Task 2

[Tigger]

I have a question about the last ToDo in Task2. It says, the image has to be projected on our 20 dimensional subspace. Why is our subspace 20 dimensional? I calculated the subspace from the 760 images in yale_faces/, which resulted in a 760 dimensional subspace.

[qgao]

I have a question about the last ToDo in Task2. It says, the image has to be projected on our 20 dimensional subspace. Why is our subspace 20 dimensional? I calculated the subspace from the 760 images in yale_faces/, which resulted in a 760 dimensional subspace.

It seems you do not well understand the concepts of space and space basis.

All eigenvectors have the dimension of number of image pixels, and composed the basis of a new space. If you use N eigenvectors as the basis, each image can be represented as a N-D vector. Thus we say the subspace is N dimensional.

[Sete]

I am a little bit confused by this issue, too. If i am not mistaken, by applying SVD on all the images we obtain 760 eigenvectors, each with a dimension of something about 8000.
So where does the "20" come from? Should we only use the 20 "most important" vectors to form our subspace?

[Tigger]

Should we only use the 20 "most important" vectors to form our subspace?

I think this is it. We choose the 20 dimensional subspace by selecting the corresponding eigenvectors. The idea is clear, i was just a little confused by the formulation of the task.

[qgao]

I am a little bit confused by this issue, too. If i am not mistaken, by applying SVD on all the images we obtain 760 eigenvectors, each with a dimension of something about 8000.
So where does the "20" come from? Should we only use the 20 "most important" vectors to form our subspace?

Right!