Add two images in MATLAB - image

Question

I am trying to overlay an activation map over a baseline vasculature image but I keep getting the same error below:
X and Y must have the same size and class or Y must be a scalar double.
I resized each to 400x400 so I thought it would work but no dice. Is there something I am missing? It is fairly straight forward for a GUI I am working on. Any help would be appreciated.
a=imread ('Vasculature.tif');
b = imresize (a, [400,400]);
c=imread ('activation.tif');
d= imresize (c, [400,400]);
e=imadd (b,d);
Could it be the bit depth or dpi?

Answer 1

I think one of your images is RGB (size(...,3)==3) and the other is grayscale (size(...,3)==1). Say the vasculature image a is grayscale and the activation image c is RGB. To convert a to RGB to match c, use ind2rgb, then add.
aRGB = ind2rgb(a,gray(256)); % assuming uint8
Alternatively, you could do aRGB = repmat(a,[1 1 3]);.
Or to put the activation image into grayscale:
cGray = rgb2gray(c);
Also, according to the documentation for imadd the two images must be:
nonsparse numeric arrays with the same size and class
To get the uint8 and uint16 images to match use the im2uint8 or im2uint16 functions to convert. Alternatively, just rescale and cast (e.g. b_uint8 = uint8(double(b)*255/65535);).
Note that in some versions of MATLAB there is a bug with displaying 16-bit images. The fix depends on whether the image is RGB or gray scale, and the platform (Windows vs. Linux). If you run into problems displaying 16-bit images, use imshow, which has the fix, or use the following code for integer data type images following image or imagesc:
function fixint16disp(img)
if any(strcmp(class(img),{'int16','uint16'}))
if size(img,3)==1,
colormap(gray(65535)); end
if ispc,
set(gcf,'Renderer','zbuffer'); end
end

Answer 2

chappjc's answers is just fine, I want to add a more general answer to the question how to solve the error message
X and Y must have the same size and class or Y must be a scalar double
General solving strategy
At which line does the error occur
Try to understand the error message
a. "... must have the same size ...":
Check the sizes of the input.
Try to understand the meaning of your code for the given (type of) input parameters. Is the error message reasonable?
What do you want to achieve?
Useful command: size A: returns the size of A
b. "... must have the same class ...":
Check the data types of the input arguments.
Which common data type is reasonable?
Convert it to the chosen data type.
Usefull command: whos A: returns all the meta information of A, i.e. size, data type, ...
Implement the solution: your favorite search engine and the matlab documentation are your best friend.
Be happy: you solved your problem and learned something new.

Answer 3

A simple code :
a=imread ('image1.jpg');
b=imresize (a, [400,400]);
subplot(3,1,1), imshow(b), title('image 1');
c=imread ('image2.jpg');
d= imresize (c, [400,400]);
subplot(3,1,2), imshow(d), title('image 2');
[x1, y1] = size(b) %height and wedth of 1st image
[x2, y2] = size(d) %height and wedth of 2nd image
for i = 1: x1
for j = 1: y1
im3(i, j)= b(i, j)+d(i, j);
end
end
subplot(3,1,3), imshow (im3), title('Resultant Image');