How to Save image using imwrite?

I1 = imread('DiseasedBW.tif') ;
I2 =imread('HealthyBW.tif') ;
I3 = imshow([I2, I2, I2; I2, I1, I2; I2, I2, I2]);
imwrite(I3,'Middisease.tif');

% Error using imwrite (line 442)
% Expected DATA to be one of these types:

% numeric, logical

% Instead its type was matlab.graphics.primitive.Image.

I want to save the following image from the above code using imwrite however keeps displaying this error. What is going wrong and how do I solve this?

Answer 1

[KSSV]

I1 = imread('DiseasedBW.tif') ;
I2 =imread('HealthyBW.tif') ;
I3 = [I2, I2, I2; I2, I1, I2; I2, I2, I2];
imwrite(I3,'Middisease.tif');