matlab algorithm question

The below link shows an algorithm I want to try and use and I have a few questions about.

Link

Firstly, I am assuming that when i=0, the first frame of a video is titled caltrain000.

for i = 0:30
imgINumber = i;
imgPNumber = i+2;

I also want to know what the below code does? Because when I try and run the code with my own video frames I get the error - "Index exceeds matrix dimensions".

imgI = imgI(:,1:352);
imgP = imgP(:,1:352);

Please help with these two questions

Answer 1

In regard to your second question,

a = a(:,1:3)

redefines a to be all rows of the current matrix, but only columns 1 through 3.

So, say

a = [ 1 2 3 4 5 6; 7 8 9 10 11 12; 13 14 15 16 17 18];

then you get

>> a = a(:,1:3)

a =

       1     2     3
       7     8     9
      13    14    15

Answer 2

When i=0, imgIFile='./caltrain/gray/caltrain000.ras'

The operation is like crop an image. All rows are selected, but only column 1 to 352 (pixel?) are selected.

Do you know why the image need to be cropped like this for motion estimation?

No idea. I guess it might be related to the size of the image.