def _obtain_input_shape(input_shape,
                        default_size,
                        min_size,
                        data_format,
                        include_top):
    """Internal utility to compute/validate an ImageNet model's input shape.
    # Arguments
        input_shape: either None (will return the default network input shape),
            or a user-provided shape to be validated.
        default_size: default input width/height for the model.
        min_size: minimum input width/height accepted by the model.
        data_format: image data format to use.
        include_top: whether the model is expected to
            be linked to a classifier via a Flatten layer.
    # Returns
        An integer shape tuple (may include None entries).
    # Raises
        ValueError: in case of invalid argument values.
    """
    if data_format == 'channels_first':
        default_shape = (3, default_size, default_size)
    else:
        default_shape = (default_size, default_size, 3)
    if include_top:
        if input_shape is not None:
            if input_shape != default_shape:
                raise ValueError('When setting`include_top=True`, '
                                 '`input_shape` should be ' + str(default_shape) + '.')
        input_shape = default_shape
    else:
        if data_format == 'channels_first':
            if input_shape is not None:
                if len(input_shape) != 3:
                    raise ValueError('`input_shape` must be a tuple of three integers.')
                if input_shape[0] != 3:
                    raise ValueError('The input must have 3 channels; got '
                                     '`input_shape=' + str(input_shape) + '`')
                if ((input_shape[1] is not None and input_shape[1] < min_size) or
                   (input_shape[2] is not None and input_shape[2] < min_size)):
                    raise ValueError('Input size must be at least ' +
                                     str(min_size) + 'x' + str(min_size) + ', got '
                                     '`input_shape=' + str(input_shape) + '`')
            else:
                input_shape = (3, None, None)
        else:
            if input_shape is not None:
                if len(input_shape) != 3:
                    raise ValueError('`input_shape` must be a tuple of three integers.')
                if input_shape[-1] != 3:
                    raise ValueError('The input must have 3 channels; got '
                                     '`input_shape=' + str(input_shape) + '`')
                if ((input_shape[0] is not None and input_shape[0] < min_size) or
                   (input_shape[1] is not None and input_shape[1] < min_size)):
                    raise ValueError('Input size must be at least ' +
                                     str(min_size) + 'x' + str(min_size) + ', got '
                                     '`input_shape=' + str(input_shape) + '`')
            else:
                input_shape = (None, None, 3)
    return input_shape