converting a cell array into numeric arrays

I am dividing images into blocks using mat2cell then i want to convert each block from cell array to a numeric array to make histogram for every block.

I need to make it in a for loop.

so what do you think?

here is my code:

 nb(1) = ceil(256/ b(1)); % number of blocks in each dimension
 nb(2) = ceil(384/ b(2)); % number of blocks in each dimension

 C=mat2cell(images,ones(256/ b(1),1)*b(1),ones(384/ b(2),1)*b(2),3);% dividing the Image into blocks.

      %C1=mat2cell(images,repmat(b(1),1,nb(1)), repmat(b(2),1,nb(2)),3);

     m=1;
      while (m < ((nb(1)*nb(2))+1))
           for i=1:nb(1)%256
              for j=1:nb(2)%384
                    [counts(i,j), x(i,j)] = imhist(C{i,j});%error
              end
           end
      end

   end
end

it gave me these errors:

??? Error using ==> iptcheckinput Function IMHIST expected its first input, I or X, to be two-dimensional.

Error in ==> imhist>parse_inputs at 281 iptcheckinput(a, {'double','uint8','int8','logical','uint16','int16','single','uint32', 'int32'}, ...

Error in ==> imhist at 59 [a, n, isScaled, top, map] = parse_inputs(varargin{:});

Error in ==> fll1 at 26 [counts(i,j), x(i,j)] = imhist(C{i,j});

Answer 1

[Sean de Wolski]

Just use cellfun with imhist as the function being applied.

As for the two dimensionality, use rgb2gray to convert your rgb image to a gray image so that data are 2-dimensional. Or use a for-loop form 1:3 to apply imhist to each slice of the third dimension.

[yasmine]

would you help me with code example for this please ?

[yasmine]

i used cellfun with imhist but this error occurred:

??? Error using ==> iptcheckinput

Function IMHIST expected its first input, I or X, to be two-dimensional.

Error in ==> imhist>parse_inputs at 281

iptcheckinput(a,

{'double','uint8','int8','logical','uint16','int16','single','uint32', 'int32'}, ...

Error in ==> imhist at 59

[a, n, isScaled, top, map] = parse_inputs(varargin{:});

Error in ==> fll1 at 22

H=cellfun(@imhist,C(:,:,1));

[Walter Roberson]

Because you did not convert your whole image to grayscale, or convert your block to grayscale, or apply imhist to each of the panes separately.

H = cellfun(@(B) imhist(rgb2gray(B)), C);

Note that your cell array C is 2 dimensional, and it is the contents of the cell that are 3 dimensional. If you wanted to just run imhist against the red plane, you could use

H = cellfun(@(B) imhist(B(:,:,1)), C);

Answer 2

[Walter Roberson]

Copied from the original thread:

You are trying to apply imhist() to a (subsection of) a truecolor image (which is thus a 3D matrix). imhist() is only for grayscale images. You should convert your whole image to grayscale before you break it up in to blocks; or you should convert each block to grayscale and imhist that as you go; or you should imhist() each of the three color planes separately.

[yasmine]

ok thank you so much for help

[yasmine]

i want to make a nested for loop to put each block in C in a separate cell then convert it to matrix using cell2mat

do you have idea ow to make it using matlab?

[Walter Roberson]

You would only convert an array of cells with cell2mat. e.g., to take a 2 x 3 cell array and unpack it back to (say) the original 37 x 19 numeric array. cell2mat should seldom be used on a single element of a cell array: to convert a single element of a cell array to numeric form, just use {} indices to reference the cell.

I think you should probably be looking in to blockproc() or blkproc() instead of worrying about mat2cell and cell2mat .

[yasmine]

yes i think so !

would you help me with code to use blkproc as i tried before and failed so i switched to mat2cell