灰度级图像水印
Gray-level Image Watermarking
图像灰度级拉伸算法
image gray-lever stretch algorithm
灰度图像的OCR识别
recognition of gray scale Optical Character Recognition
灰度图像加密
encryptions of gray scale image
图像灰度差值法
Image subtracting operation
图像灰度跳变特征
Gray-scale transformation features