def denormalize(img, mean, std):
    """
    Denormalize the image with mean and standard deviation. This inverts
    the normalization.
    
    Parameters
    ----------
    img : array(float)
        The image to denormalize.
    mean : float
        The mean which was used for normalization.
    std : float
        The standard deviation which was used for normalization.
    """
    return (img * std) + mean