I am trying to use blockproc (A,[8 8 ],dct2) to create a block of 8X8 from A image of 600X800 it does not works as they are telling me that dct2 is not a handle function . what is the exact argument I have to use instead of dct2?

A = imread('C:\lesloges.png'); B= rgb2gray(A); B=double(B)/255.0;

C= blockproc(B,[8 8],dct2);

Error using dct2 (line 45) Not enough input arguments.

Error in essaidecoupagebloc88 (line 11) C= blockproc(B,[8 8],dct2)

[Geoff Hayes]

According to http://www.mathworks.com/help/images/ref/blockproc.html#inputarg_fun, a function handle is required. Try putting an ampersand in front of dct2:

 C= blockproc(B,[8 8],@dct2);

Note that if I do

 y = @dct2;

then class(y) returns function_handle.

[yaowu groshenry]

thanks but is does not seem to work.I wrote:

A=imread('C:\Users\ygroshen\Desktop\fleurslesloges.png');

I=rgb2gray(A);

y=@dct2;

J= blockproc(I,[8 8],y);

imshow(J)

I have this error message:

Function BLOCKPROC encountered an error while evaluating the user supplied function handle, FUN.

The cause of the error was:

Error using double Conversion to double from struct is not possible.

Error in dct (line 27) a = double(a);

Error in dct2 (line 67) b = dct(a, mpad);

Error in blockprocFunDispatcher (line 13) output_block = fun(block_struct);

Error in blockprocInMemory (line 80) [ul_output fun_nargout] = blockprocFunDispatcher(fun,block_struct,...

Error in blockproc (line 236) result_image = blockprocInMemory(source,fun,options);

Error in codedJPEGavecIMTB (line 5) J= blockproc(I,[8 8],y);

Answer 1

[Geoff Hayes]

The documentation for the blockproc function (see http://www.mathworks.com/help/images/ref/blockproc.html for details) indicates that the function handle must be to a function that accepts a block struct as input and returns a matrix, vector, or scalar. Your function, dct2, accepts a matrix only, not a structure. So you will have to do something like the example from the blockproc link:

 % their example
 fun = @(block_struct) imresize(block_struct.data,0.15);

 % your code
 fun = @(block_struct) dct2(block_struct.data);
 J   = blockproc(I,[8 8],fun);

Try the above and see if it helps.

[Lu]

Errors:

Answer 2

[Meshooo]

Hi Lu,

Check the following url, it shows a very good example for block processing.

http://matlabf1.blogspot.jp/2012/10/threshold-and-histogram.html

Hope it helps you.

Meshoo