Matrix Multiplication Problem. Different Data Types.

Hi.. I have already posted a question before: http://mathworks.com/matlabcentral/answers/13018-array-of-matrices#answer_17796

This is sort of an extension of it.

My problem is, I do this:

A=imread(A) B=dct2(A) M=B*A*B'

Now, the final statement gives me an error since A is uint8 and B is double.

So what I did is, before the third step, I did: A=double(A)

Now, on doing imshow(A)...my entire image has changed from being that of a retina scan into a blank white image. I understand this is because of the type change, but the question is....will this cause any precision change in the multiplication that I am carrying out? After all, it is the value of M that is my main aim to find.

Also, on inserting a value in a 3D matrix array, I have to see the content of thousands of lines. Is there any way to stop that?

Answer 1

[Jan]

Instead of A = double(A), you can normalize the values to the intervall [0, 1]:

A = double(A) / 255

You can suppress the dispaly of the complete arrays by closing the statement with a semicolon:

A = rand(3);
A(1) = 5   % A is displayed
A(2) = 5;  % A is not displayed

Answer 2

[Walter Roberson]

As I already indicated hours ago, instead of using double(A), I suggest you use im2double(A)

This is more general than Jan's solution in that im2double() will detect the proper scaling factor instead of assuming uint8.