像素范围处理 saturate_cast<char>( )  ，确保RGB的值在0~255

掩膜操作实现图像对比度，

代码片段三（提高对比度）：

#include<opencv2/opencv.hpp>
#include<iostream>
#include<math.h>

using namespace cv;
int main(int argc, char ** argv) {
	Mat src, dst;
	src= imread("D:/newWorkSpace/image.png");
	if (src.empty()) {
		printf("could not load image...\n");
		return -1;
	}
	namedWindow("input image", CV_WINDOW_AUTOSIZE);
	imshow("input image", src);

	int cols = src.cols * src.channels();
	int offsetx = src.channels();
	int rows = src.rows;
	
	dst = Mat::zeros(src.size(), src.type());
	for (int row = 1; row < (rows - 1);row++) {
		const uchar* previous = src.ptr<uchar>(row - 1);
		const uchar* current = src.ptr<uchar>(row);
		const uchar* next = src.ptr<uchar>(row + 1);
		uchar* output = dst.ptr<uchar>(row);
		for (int col = offsetx; col < cols; col++) {
			output[col] = saturate_cast<uchar>(5 * current[col] - (current[col - offsetx] + current[col + offsetx] + previous[col] + next[col]));
		}
	}

	namedWindow("output image", CV_WINDOW_AUTOSIZE);
	imshow("output image", dst);

	waitKey(0);
	return 0;
}

可替换为：

        double t = getTickCount();
	Mat kernel = (Mat_<char>(3, 3) << 0, -1, 0, -1, 5, -1, 0, -1, 0);
	filter2D(src, dst, src.depth(), kernel);
	double timeconsume = (getTickCount() - t) / getTickFrequency();
	printf("tim consume %.2f\n", timeconsume);