IHS wavelet image fusion

The code uses two images one panchromatic and other multispectral. The images are to be fused using IHS based wavelet image fusion technique.I am using the following code for image fusion but facing problem at the end line:

img_pan = imread('C:\Documents and Settings\admin\Desktop\TM\tanya\img3.tif'); 
img_msi = imread('C:\Documents and Settings\admin\Desktop\TM\tanya\img4.tif');
[r c] = size(img_pan);
img_msi_re = imresize(img_msi,[r c],'bilinear');

img_pan=im2double(img_pan);
img_msi=im2double(img_msi);
r=img_msi(:,:,1);
g=img_msi(:,:,2);
b=img_msi(:,:,3);
th=acos((0.5*((r-g)+(r-b)))./((sqrt((r-g).^2+(r-b).*(g-b)))+eps));
H=th;
H(b>g)=2*pi-H(b>g);
H=H/(2*pi);
S=1-3.*(min(min(r,g),b))./(r+g+b+eps);
I=(r+g+b)/3;
hsi=cat(3,H,S,I);
HE=H*2*pi;
HE=histeq(HE);
HE=HE/(2*pi);
SE=histeq(S);
IE=histeq(I);
figure, imshow(hsi),title('HSI Image');
img_msi_re_hsi = hsi;
I = img_msi_re_hsi(:,:,3);
hespc = imhist(I);

img_pan_histeq = histeq(img_msi,hespc);

error:

??? Error using ==> iptcheckinput
Function HISTEQ expected its first input, I, to be two-dimensional.

Error in ==> histeq at 100
      iptcheckinput(a,{'uint8','uint16','double','int16','single'}, ...