def batch_center_crop_frac(batch_image, frac):
    """
    Args:
        batch_image: [b, h, w, c]
        frac: 0.5, 0.75

    """
    b, h, w, c =  batch_image.get_shape().as_list()
    start_h = int((h - frac * h)/2)
    start_w = int((w - frac * w)/2)
    
    end_h = start_h + int(frac * h)
    end_w = start_w + int(frac * w)

    croped_image = batch_image[:, start_h:end_h, start_w:end_w,:]

    return croped_image