中文说明：灰度扩展及灰度图像伪彩色化：灰度值在0～20之间显蓝色，20～40之间显绿色，40～255显红色。
English Description：
Grayscale expansion and pseudo colorization of grayscale image: the grayscale value between 0 and 20 shows blue, between 20 and 40 shows green, and between 40 and 255 shows red.