how to rewrite a 2d image matrix as 3d matrix and operate further

i am doing digital watermarking using svd+dwt. at the time of extracting the watermark i have a problem that my original watermark is a colored image and the watermarked image is also in color but on applying svd i took only the red components but on combining it is showing the error that " Subscripted assignment dimension mismatch" please help!

[Image Analyst]

How can we do that? Give us all the red text that is the error message. Also give the snippet of code around the error, or attach the m-file.