Undefined function 'mtimes' for input arguments of type 'struct'. Error in @(a)T*a*T' Error in blockprocFunDispatcher (line 13)

I am doing jpeg compression. I will imlement dct to image with blockproc. When I want to working the below code Matlab is giving that problem. Can you help me for solve this problem. After I will quantization process this code..

    %
clc
clear all
close all
f = imread('monkey.tif');
g1 = rgb2gray(f);
g1 = im2double(g1);
%imshow(g1);
T = dctmtx(8);
dct_2 = @(x)T*x*T';
A = blockproc(g1, [8 8], dct_2);

Answer 1

[dpb]

You must reference the structure field content to have an array as input to the function. Example...

>>  s.x=rand(2);  % create a structure, fieldname 'x' as 2x2 array
>>  abs(s)        % take absolute value (I don't have Toolbox, same issue)
Undefined function 'abs' for input arguments of type 'struct'. 
>> abs(s.x)    % now refer to the field
ans =
  0.2760    0.6551
  0.6797    0.1626
>>

Or, you could have (perhaps inadvertently) created a nested structure that would cause same thing but at deeper level --

>> t.s=s  % create structure containing structure
t = 
  s: [1x1 struct]
>> abs(t)
Undefined function 'abs' for input arguments of type 'struct'. 
>> abs(t.s)
Undefined function 'abs' for input arguments of type 'struct'. 
>> abs(t.s.x)
ans =
  0.2760    0.6551
  0.6797    0.1626
>>

We can't know what you did precisely w/o seeing the definition for the data and the actual code usage besides the error.

ADDENDUM

Ah, with the function handle definition in line it's easier to see/pick out the issue -- examples did illustrate the error, just not so simple to see what the root cause was--

Note the requirement that the function accept a block_struct

From the example for blockproc

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

So, your function needs to refer to x.data to refer to the data, x in the argument is the structure.

dct_2 = @(x)T*x.data*T';

[murat alboga]

Sorry dbp, Thanks your answers. I added my little code. If you want to check again my code problems.

[dpb]

Ah, that's easier -- see updated Answer.