how to write matrix into geotiff format

Hello, I have an image made in ArcGIS. its format is Geotiff. I raed it with below command in matlab:

    [X, cmap, R] = geotiffread('sarea.tif')

Then I made some changes in matrix X. finally I decided to convert it to previous format (Geotiff) to read in ArcGIS. Therefore I used the below code:

    geotiffwrite('aa.tif',X,cmap,R)

But I got the error:

    ??? Error using ==> geotiffwrite
Expected input number 2, X, to be one of these types:

uint8, uint16
Instead its type was single.
Error in ==> geotiffwrite>validateImage at 395
  validateattributes(A, {'uint8','uint16'}, {'nonempty'}, ...
Error in ==> geotiffwrite>validateInputs at 343
[A, cmap] = validateImage(A, cmap);
Error in ==> geotiffwrite at 233
[filename, A, cmap, R, Params] = validateInputs( ...

I convert X to uint8 using

    X=uint8(X)

But again I got the error:

    geotiffwrite('aa.tif',X,cmap,R)
??? Error using ==> checkcmap at 16
Function GEOTIFFWRITE expected its third input argument CMAP to be a valid colormap. Valid
colormaps must be nonempty, double, 2-D matrices with 3 columns.
Error in ==> geotiffwrite>validateImage at 397
    internal.map.checkcmap(cmap, mfilename, 'CMAP', 3)
Error in ==> geotiffwrite>validateInputs at 343
[A, cmap] = validateImage(A, cmap);
Error in ==> geotiffwrite at 233
[filename, A, cmap, R, Params] = validateInputs( ...

Why I got the error? What is problem? Thank you