def _surf_smooth_single(image,outfile,dilation,smooth,threshold,inflation,alpha,
    cut_idx,cut_side,overlay,overlay_mask,overlay_cmap,overlay_scale, 
    overlay_alpha,rotation,grayscale,bg_grayscale,verbose):
    """
    Generate a surface of the smooth white matter of a brain image. 

    This is great for displaying functional activations as are typically seen
    in the neuroimaging literature.

    Arguments
    ---------
    image : ANTsImage
        A binary segmentation of the white matter surface.
        If you don't have a white matter segmentation, you can use
        `kmeans_segmentation` or `atropos` on a full-brain image.
    
    inflation : integer
        how much to inflate the final surface

    rotation : 3-tuple | string | list of 3-tuples | list of string
        if tuple, this is rotation of X, Y, Z 
        if string, this is a canonical view..
            Options: 'left', 'right', 'inner_left', 'inner_right', 
            'anterior', 'posterior', 'inferior', 'superior'
        if list of tuples or strings, the surface images will be arranged
        in a grid according to the shape of the list.
        
        e.g. rotation=[['left', 'inner_left' ],
                       ['right','inner_right']] 
        will result in a 2x2 grid of the above 4 canonical views
    
    grayscale : float
        value between 0 and 1 representing how light to make the base image.
        grayscale = 1 will make the base image completely white and 
        grayscale = 0 will make the base image completely black

    background : float
        value between 0 and 1 representing how light to make the base image.
        see `grayscale` arg.

    outfile : string
        filepath to which the surface plot will be saved

    Example
    -------
    >>> import ants
    >>> mni = ants.image_read(ants.get_data('mni'))
    >>> seg = mni.otsu_segmentation(k=3)
    >>> wm_img = seg.threshold_image(3,3)
    >>> #ants.surf_smooth(wm_img, outfile='~/desktop/surf_smooth.png')
    >>> ants.surf_smooth(wm_img, rotation='inner_right', outfile='~/desktop/surf_smooth_innerright.png')
    >>> # with overlay
    >>> overlay = ants.weingarten_image_curvature( mni, 1.5  ).smooth_image( 1 ).iMath_GD(3)
    >>> ants.surf_smooth(image=wm_img, overlay=overlay, outfile='~/desktop/surf_smooth2.png')
    """

    # handle rotation argument
    if rotation is None:
        rotation = (270,0,270)
    if not isinstance(rotation, (str, tuple)):
        raise ValueError('rotation must be a 3-tuple or string')
    if isinstance(rotation, str):
        if 'inner' in rotation:
            cut_idx = int(image.shape[2]/2)
            cut_side = rotation.replace('inner_','')
        rotation = _view_map[rotation.lower()]


    # handle filename argument
    if outfile is None:
        outfile = mktemp(suffix='.png')
    else:
        outfile = os.path.expanduser(outfile)

    # handle overlay argument
    if overlay is not None:
        if overlay_mask is None:
            overlay_mask = image.iMath_MD(3)

    # PROCESSING IMAGE
    image = image.reorient_image2('RPI')
    image = image.iMath_fill_holes().iMath_get_largest_component()
    if dilation > 0:
        image = image.iMath_MD(dilation)
    if smooth > 0:
        image = image.smooth_image(smooth)
    if threshold > 0:
        image = image.threshold_image(threshold)
    if cut_idx is not None:
        if cut_side == 'left':
            image = image.crop_indices((0,0,0),(cut_idx,image.shape[1],image.shape[2]))
        elif cut_side == 'right':
            image = image.crop_indices((cut_idx,0,0),image.shape)
        else:
            raise ValueError('not valid cut_side argument')

    # surface arg
    # save base image to temp file
    image_tmp_file = mktemp(suffix='.nii.gz')
    image.to_file(image_tmp_file)
    # build image color
    grayscale = int(grayscale*255)
    alpha = 1.
    image_color = '%sx%.1f' % ('x'.join([str(grayscale)]*3),
                               alpha)
    cmd = '-s [%s,%s] ' % (image_tmp_file, image_color)

    # anti-alias arg
    tolerance = 0.01
    cmd += '-a %.3f ' % tolerance

    # inflation arg
    cmd += '-i %i ' % inflation

    # display arg
    bg_grayscale = int(bg_grayscale*255)
    cmd += '-d %s[%s,%s]' % (outfile,
                              'x'.join([str(s) for s in rotation]),
                              'x'.join([str(bg_grayscale)]*3))

    # overlay arg
    if overlay is not None:
        overlay = overlay.reorient_image2('RPI')
        if overlay_scale == True:
            min_overlay, max_overlay = overlay.quantile((0.05,0.95))
            overlay[overlay<min_overlay] = min_overlay
            overlay[overlay>max_overlay] = max_overlay
        elif isinstance(overlay_scale, tuple):
            min_overlay, max_overlay = overlay.quantile((overlay_scale[0], overlay_scale[1]))
            overlay[overlay<min_overlay] = min_overlay
            overlay[overlay>max_overlay] = max_overlay

        # make tempfile for overlay
        overlay_tmp_file = mktemp(suffix='.nii.gz')
        # convert overlay image to RGB
        overlay.scalar_to_rgb(mask=overlay_mask, cmap=overlay_cmap,
                              filename=overlay_tmp_file)
        # make tempfile for overlay mask
        overlay_mask_tmp_file = mktemp(suffix='.nii.gz')
        overlay_mask.to_file(overlay_mask_tmp_file)

        cmd += ' -f [%s,%s,%.2f]' % (overlay_tmp_file, overlay_mask_tmp_file, overlay_alpha)

    if verbose:
        print(cmd)
        time.sleep(1)

    cmd = cmd.split(' ')
    libfn = utils.get_lib_fn('antsSurf')
    retval = libfn(cmd)
    if retval != 0:
        print('ERROR: Non-Zero Return Value!')

    # cleanup temp file
    os.remove(image_tmp_file)
Generate a surface of the smooth white matter of a brain image. 

    This is great for displaying functional activations as are typically seen
    in the neuroimaging literature.

    Arguments
    ---------
    image : ANTsImage
        A binary segmentation of the white matter surface.
        If you don't have a white matter segmentation, you can use
        `kmeans_segmentation` or `atropos` on a full-brain image.
    
    inflation : integer
        how much to inflate the final surface

    rotation : 3-tuple | string | list of 3-tuples | list of string
        if tuple, this is rotation of X, Y, Z 
        if string, this is a canonical view..
            Options: 'left', 'right', 'inner_left', 'inner_right', 
            'anterior', 'posterior', 'inferior', 'superior'
        if list of tuples or strings, the surface images will be arranged
        in a grid according to the shape of the list.
        
        e.g. rotation=[['left', 'inner_left' ],
                       ['right','inner_right']] 
        will result in a 2x2 grid of the above 4 canonical views
    
    grayscale : float
        value between 0 and 1 representing how light to make the base image.
        grayscale = 1 will make the base image completely white and 
        grayscale = 0 will make the base image completely black

    background : float
        value between 0 and 1 representing how light to make the base image.
        see `grayscale` arg.

    outfile : string
        filepath to which the surface plot will be saved

    Example
    -------
    >>> import ants
    >>> mni = ants.image_read(ants.get_data('mni'))
    >>> seg = mni.otsu_segmentation(k=3)
    >>> wm_img = seg.threshold_image(3,3)
    >>> #ants.surf_smooth(wm_img, outfile='~/desktop/surf_smooth.png')
    >>> ants.surf_smooth(wm_img, rotation='inner_right', outfile='~/desktop/surf_smooth_innerright.png')
    >>> # with overlay
    >>> overlay = ants.weingarten_image_curvature( mni, 1.5  ).smooth_image( 1 ).iMath_GD(3)
    >>> ants.surf_smooth(image=wm_img, overlay=overlay, outfile='~/desktop/surf_smooth2.png')