Image arrays and converting matrix to line

Can someone explain what each line is doing in this code and how it's doing it, if possible?

I commented the best I could to get a general understanding of what's going on. But I don't understand it in detail. Like what the main lines of code are actually doing.

    for i=1:10   
      FName=sprintf('%d.bmp',i);
      image1=imread([FFolder1, FName]);
       % Creating a 3D image for every number and implementing it in every loop
        im1(:,:,i)=image1;      % "A"
    end
  for i=1:M   
      FName=sprintf('%d.bmp',i+10);
      image1t=imread([FFolder1, FName]);
        im1t(:,:,i)=image1t;      % "A"
    end

for i=1:10   % Training images
    im(:,:,i)=im1(:,:,i);
end
for i=1:20   
    imt(:,:,i)=im1t(:,:,i);
end
      % The transition of values (0 1) to the range (0: 255)
  for i=1:10*10   % Training images
      imd(:,:,i)=(im2double(im(:,:,i)));
  end
for i=1:10*20   
    imdt(:,:,i)=(im2double(imt(:,:,i)));
end

    for s=1:10*10
        for i=1:40
            for j=1:120
                Xv(s,(i-1)*120+j)=imd(j,i,s);
            end
        end
    end
    sizeXv=size(Xv);

Answer 1

[Walter Roberson]

There is a lot there which is inefficient.

The first two loops do not create a 3D array for each number. They read images as "slices" in a 3D array.

The code

for i=1:N   % Training images
    im(:,:,i)=im1(:,:,i);
end

can be coded much more compactly as

 im = im1;

since im1 is exactly N panes long anyhow. Likewise the training and test can be done by simple copying of entire arrays.

For

for i=1:10*N   % Training images
    imd(:,:,i)=(im2double(im(:,:,i)));
end

you might prefer this code, but it is not the most efficient. More efficient would be to work on the entire array at one time,

if isa(im, 'uint8')              %bmp can be logical or 8 bit or 24 but not 16 bit
  imd = double(im) ./ (2^8-1);
else
  imd = double(im);
end

and if you were sure ahead of time which data class it was going to be, you could optimize that. I suspect you are working with uint8 images.

The last bit could be rewritten as

Xv = reshape(imd, size(imd,1)*size(imd,2), size(imd,3)) .';