请教加高斯噪声的问题

[ljlj521521521]

I=imread('.\草原.jpg');
c=20;
[m,n,color]=size(I);
B1=awgn(I(:,:,1),c);
B2=awgn(I(:,:,2),c);
B3=awgn(I(:,:,3),c);
I(:,:,1)= B1;
I(:,:,2)= B2;
I(:,:,3)= B3;
imshow(I)

对图像在单通道下加入高斯噪声，代码如上，调试时会报错
??? Error using ==> plus
Integers can only be combined with integers of the same class, or scalar doubles.

Error in ==> awgn at 247
y = sig+wgn(size(sig,1), size(sig,2), noisePower, 1, state, pMode, opType);

Error in ==> testawgn at 4
B1=awgn(I(:,:,1),c);
请教各位大侠该如何修改，谢谢