matrix dimensions must agree error

%I want to use dct2 to an image array and quantize 4x4 blocks of the image

%but in [afteral]=quantization(imafter,25); command it says "matrix dimensions must agree"

%IGNORE integer_transform its just another function I use.

frame178=imread("frame178.tif");

quantize = @(block_struct) integer_transform(dct2(block_struct.data));

imafter = blockproc(frame178,[4 4],quantize);

[afteral]= quantization(imafter,25);

%the function :

function [Z] = quantization(W,QP)

Z = round(W.*(M/2^q));

%THIS IS THE FUNCTION DEFINITION AND THE LINE WHERE IS THE ERROR

%M and q are defined before in the function M is a matrix with some factors and q is an integer

%I assume Z the error is the inserted matrix M that is different size from Z but when I do

%multiply with x.*y dont I multiply all elements of an array(W) with an integer from a matrix(M)? so why to have size error there?

Answer 1

[Image Analyst]

It's not Z that matters. It's W.

What does this report in the command window if you put it before that Z line:

whos W
whos M
whos q

[Lefteris Kostakis]

W 144x176 double (the parameter in function is array frame178 and its also 144x176 but not double it is uint8)

M 4x4 double

q 1x1 double

[Image Analyst]

So why do you think it's okay to do an element-by-element operation of a 144x176 matrix by a 4x4 matrix?

What happens when it goes to multiply W(5, 1) by M(5, 1) when there is no M(5,1)?

It can't multiply elements when the elements are not there.