DCT example gives me an error when using a different picture

Hello, I've been trying to compress an image using the DCT example provided here , but when I put my own images it gives me this error:

BLOCKPROC encountered an error while evaluating the user-supplied function handle, FUN.

The cause of the error was:

Error using  * 
Arguments must be 2-D, or at least one argument must be scalar. Use TIMES (.*) for elementwise multiplication.

Error in ImageCompression>@(block_struct)T*block_struct.data*T'

Error in blockprocFunDispatcher (line 13)
        output_block = fun(block_struct);

Error in blockprocInMemory (line 80)
[ul_output fun_nargout] = blockprocFunDispatcher(fun,block_struct,...

Error in blockproc (line 243)
    result_image = blockprocInMemory(source,fun,options);

Error in ImageCompression (line 6)
B = blockproc(I,[8 8],dct);

Answer 1

[Walter Roberson]

You are probably passing in rgb images .

Note that although jpg in theory can handle greyscale images in practice greyscale jpg are very rare and nearly all grey appearing jpg are stored as rgb

[Yiannis Hadjicharalambous]

Yeah I'm passing in RGB images. Is there another example that can do image compression with RGB images?