def compress_under_size(imagefile, targetfile, targetsize):
    """压缩图片尺寸直到某一尺寸

    :param imagefile: 原图路径
    :param targetfile: 保存图片路径
    :param targetsize: 目标大小，单位byte
    """
    currentsize = os.path.getsize(imagefile)
    for quality in range(99, 0, -1):  # 压缩质量递减
        if currentsize > targetsize:
            image = Image.open(imagefile)
            image.save(targetfile, optimize=True, quality=quality)
            currentsize = os.path.getsize(targetfile)


if __name__ == '__main__':
    imagefile = './input/t1.jpg'  # 图片路径
    targetfile = './output/zm.jpg'  # 目标图片路径
    targetsize = 2048 * 1024  # 目标图片大小
    compress_under_size(imagefile, targetfile, targetsize)  # 将图片压缩到2M