Unable to use multiplication with grayscale image matrix

Question

I am quite new to matlab/octave. I loaded an image using imread() function of octave. I tried to perform multiplication operation on the matrix but get the following error:

binary operator `*' not implemented for `uint8 matrix' by `matrix' operations 

Is there another way to input the image??

Answer 1

I=imread('...');
I=rgb2gray(I);
I=double(I);
% you can perform the multiplication operation now

Answer 2

This usually means that you are trying to multiply arrays of different data types. The easiest thing to do here is to convert the uint8 image into double. You can either use the double() function, which will just cast the values, or us im2double(), which will also normalize the values to be between 0 and 1.