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OpenCV 圖像對(duì)比度的實(shí)踐

更新時(shí)間：2021年09月05日 10:15:49 作者：翟天保Steven

本文主要介紹了OpenCV 圖像對(duì)比度的實(shí)踐，文中通過(guò)示例代碼介紹的非常詳細(xì)，具有一定的參考價(jià)值，感興趣的小伙伴們可以參考一下

本文主要介紹了OpenCV 圖像對(duì)比度，具有一定的參考價(jià)值，感興趣的可以了解一下

實(shí)現(xiàn)原理

圖像對(duì)比度指的是一幅圖像中明暗區(qū)域最亮的白和最暗的黑之間不同亮度層級(jí)的測(cè)量，即指一幅圖像灰度反差的大小。差異范圍越大代表對(duì)比越大，差異范圍越小代表對(duì)比越小。設(shè)置一個(gè)基準(zhǔn)值thresh，當(dāng)percent大于0時(shí)，需要令圖像中的顏色對(duì)比更強(qiáng)烈，即數(shù)值距離thresh越遠(yuǎn)，則變化越大；當(dāng)percent等于1時(shí)，對(duì)比強(qiáng)到極致，只有255和0的區(qū)分；當(dāng)percent等于0時(shí)，不變；當(dāng)percent小于0時(shí)，對(duì)比下降，即令遠(yuǎn)離thresh的數(shù)值更近些；當(dāng)percent等于-1時(shí)，沒(méi)有對(duì)比了，全是thresh值。

對(duì)比度調(diào)整算法的實(shí)現(xiàn)流程如下：

1.設(shè)置調(diào)整參數(shù)percent，取值為-100到100，類(lèi)似PS中設(shè)置，歸一化后為-1到1。

2.針對(duì)圖像所有像素點(diǎn)單個(gè)處理。當(dāng)percent大于等于0時(shí)，對(duì)比增強(qiáng)，調(diào)整后的RGB三通道數(shù)值為：

3.若percent小于0時(shí)，對(duì)比降低，此時(shí)調(diào)整后的圖像RGB三通道值為：

4.若percent等于1時(shí)，大于thresh則等于255，小于則等于0。

至此，圖像實(shí)現(xiàn)了明度的調(diào)整，算法邏輯參考xingyanxiao。C++實(shí)現(xiàn)代碼如下。

功能函數(shù)代碼

// 對(duì)比度
cv::Mat Contrast(cv::Mat src, int percent)
{
	float alpha = percent / 100.f;
	alpha = max(-1.f, min(1.f, alpha));
	cv::Mat temp = src.clone();
	int row = src.rows;
	int col = src.cols;
	int thresh = 127;
	for (int i = 0; i < row; ++i)
	{
		uchar *t = temp.ptr<uchar>(i);
		uchar *s = src.ptr<uchar>(i);
		for (int j = 0; j < col; ++j)
		{
			uchar b = s[3 * j];
			uchar g = s[3 * j + 1];
			uchar r = s[3 * j + 2];
			int newb, newg, newr;
			if (alpha == 1)
			{
				t[3 * j + 2] = r > thresh ? 255 : 0;
				t[3 * j + 1] = g > thresh ? 255 : 0;
				t[3 * j] = b > thresh ? 255 : 0;
				continue;
			}
			else if (alpha >= 0)
			{
				newr = static_cast<int>(thresh + (r - thresh) / (1 - alpha));
				newg = static_cast<int>(thresh + (g - thresh) / (1 - alpha));
				newb = static_cast<int>(thresh + (b - thresh) / (1 - alpha));
			}
			else {
				newr = static_cast<int>(thresh + (r - thresh) * (1 + alpha));
				newg = static_cast<int>(thresh + (g - thresh) * (1 + alpha));
				newb = static_cast<int>(thresh + (b - thresh) * (1 + alpha));
 
			}
			newr = max(0, min(255, newr));
			newg = max(0, min(255, newg));
			newb = max(0, min(255, newb));
			t[3 * j + 2] = static_cast<uchar>(newr);
			t[3 * j + 1] = static_cast<uchar>(newg);
			t[3 * j] = static_cast<uchar>(newb);
		}
	}
	return temp;
}

C++測(cè)試代碼

#include <opencv2/opencv.hpp>
#include <iostream>
using namespace cv;
using namespace std;
 
cv::Mat Contrast(cv::Mat src, int percent);
 
int main()
{
	cv::Mat src = imread("5.jpg");
	cv::Mat result = Contrast(src, 50.f);
	imshow("original", src);
	imshow("result", result);
	waitKey(0);
	return 0;
}
 
// 對(duì)比度
cv::Mat Contrast(cv::Mat src, int percent)
{
	float alpha = percent / 100.f;
	alpha = max(-1.f, min(1.f, alpha));
	cv::Mat temp = src.clone();
	int row = src.rows;
	int col = src.cols;
	int thresh = 127;
	for (int i = 0; i < row; ++i)
	{
		uchar *t = temp.ptr<uchar>(i);
		uchar *s = src.ptr<uchar>(i);
		for (int j = 0; j < col; ++j)
		{
			uchar b = s[3 * j];
			uchar g = s[3 * j + 1];
			uchar r = s[3 * j + 2];
			int newb, newg, newr;
			if (alpha == 1)
			{
				t[3 * j + 2] = r > thresh ? 255 : 0;
				t[3 * j + 1] = g > thresh ? 255 : 0;
				t[3 * j] = b > thresh ? 255 : 0;
				continue;
			}
			else if (alpha >= 0)
			{
				newr = static_cast<int>(thresh + (r - thresh) / (1 - alpha));
				newg = static_cast<int>(thresh + (g - thresh) / (1 - alpha));
				newb = static_cast<int>(thresh + (b - thresh) / (1 - alpha));
			}
			else {
				newr = static_cast<int>(thresh + (r - thresh) * (1 + alpha));
				newg = static_cast<int>(thresh + (g - thresh) * (1 + alpha));
				newb = static_cast<int>(thresh + (b - thresh) * (1 + alpha));
 
			}
			newr = max(0, min(255, newr));
			newg = max(0, min(255, newg));
			newb = max(0, min(255, newb));
			t[3 * j + 2] = static_cast<uchar>(newr);
			t[3 * j + 1] = static_cast<uchar>(newg);
			t[3 * j] = static_cast<uchar>(newb);
		}
	}
	return temp;
}