opencv灰度图转伪彩图或彩色图

一般例如红外图像，呈现出来的是灰度图效果，此时每个像素有一个，在0-255内，如果想要观看伪彩图，也就是人工设置的彩色，需要在灰度图的基础上，给它增加RGB三个通道的值，让它变为看起来有红绿蓝叠加的彩色效果，原理也就是把1个灰度值变为3个值RGB。

#include 
using namespace cv;
using namespace std;

Mat scaleGray(const Mat& inputGray)
{
	Mat outputGray(inputGray.size(), CV_8U);
	unsigned char grayValue, maxValue = 1;
	for (int y = 0; y < inputGray.rows; y++)
		for (int x = 0; x < inputGray.cols; x++)
		{
			grayValue = inputGray.at(y, x);
			maxValue = max(maxValue, grayValue);
		}

	float scale = 255.0 / maxValue;
	for (int y = 0; y < inputGray.rows; y++)
		for (int x = 0; x < inputGray.cols; x++)
		{
			outputGray.at(y, x) = static_cast(inputGray.at(y, x) * scale + 0.5);
		}

	return outputGray;
}

Mat gray2pseudocolor(const Mat& scaledGray)
{
	Mat outputPseudocolor(scaledGray.size(), CV_8UC3);
	unsigned char grayValue;
	for (int y = 0; y < scaledGray.rows; y++)
		for (int x = 0; x < scaledGray.cols; x++)
		{
			//获取灰度值
			grayValue = scaledGray.at(y, x);
			Vec3b& pixel = outputPseudocolor.at(y, x);
			//给mat的RGB三通道赋值  orange  255 127 0
			pixel[0] = abs(255 - grayValue);
			pixel[1] = abs(127 - grayValue);
			pixel[2] = abs(0 - grayValue);
		}

	return outputPseudocolor;
}


Mat gray2rainbow(const Mat& scaledGray)
{
	Mat outputRainbow(scaledGray.size(), CV_8UC3);
	unsigned char grayValue;
	for (int y = 0; y < scaledGray.rows; y++)
		for (int x = 0; x < scaledGray.cols; x++)
		{
			grayValue = scaledGray.at(y, x);
			Vec3b& pixel = outputRainbow.at(y, x);
			//对灰度值进行分阶段处理，让色彩更丰富
			if (grayValue <= 51)
			{
				pixel[0] = 255;
				pixel[1] = grayValue * 5;
				pixel[2] = 0;
			}
			else if (grayValue <= 102)
			{
				grayValue -= 51;
				pixel[0] = 255 - grayValue * 5;
				pixel[1] = 255;
				pixel[2] = 0;
			}
			else if (grayValue <= 153)
			{
				grayValue -= 102;
				pixel[0] = 0;
				pixel[1] = 255;
				pixel[2] = grayValue * 5;
			}
			else if (grayValue <= 204)
			{
				grayValue -= 153;
				pixel[0] = 0;
				pixel[1] = 255 - static_cast(grayValue * 128.0 / 51 + 0.5);
				pixel[2] = 255;
			}
			else if (grayValue <= 255)
			{
				grayValue -= 204;
				pixel[0] = 0;
				pixel[1] = 127 - static_cast(grayValue * 127.0 / 51 + 0.5);
				pixel[2] = 255;
			}
		}

	return outputRainbow;
}

int main(int argc, char* argv[])
{

	Mat inputGray = imread("red-2022-3-27_20-25-42.jpg", 0);
	Mat scaledGray = scaleGray(inputGray);
	//伪彩
	Mat pseudocolor = gray2pseudocolor(scaledGray);
	//五彩缤纷
	Mat rainbow = gray2rainbow(scaledGray);

	imwrite("scaledGray.jpg", scaledGray);
	imwrite("pseudocolor.jpg", pseudocolor);
	imwrite("rainbow.jpg", rainbow);

	namedWindow("gray", WINDOW_NORMAL);
	resizeWindow("gray", 640, 480);
	//移动窗口位置
	moveWindow("gray", 100, 20);
	imshow("gray", inputGray);

	namedWindow("pseudocolor", WINDOW_NORMAL);
	resizeWindow("pseudocolor", 640, 480);
	//移动窗口位置
	moveWindow("pseudocolor", 740, 20);
	imshow("pseudocolor", pseudocolor);

	namedWindow("rainbow", WINDOW_NORMAL);
	resizeWindow("rainbow", 640, 480);
	//移动窗口位置
	moveWindow("rainbow", 740, 500);
	imshow("rainbow", rainbow);

	waitKey(0);

	return 0;
}