如果你想加強一幅圖像的對比度，可以給每個像素的值都乘以一個大于1的常數

\[ new\_image (i, j) = image(i, j) * c \]

其中 \(c > 1\)

如果你想減弱一幅圖像的對比度，可以給每個像素的值都乘以一個大于0且小于1的常數

\[ new\_image (i, j) = image(i, j) * c \]

其中 \(0 < c < 1\)

Code

/* 作者：鄭大峰 時間：2019年09月20日 環境：OpenCV 4.1.1 + VS2017 內容：Change Contrast */#include "pch.h" #include <iostream> #include <opencv2/opencv.hpp>using namespace std; using namespace cv;int main() {Mat image = imread("claudia.png");if (image.empty()){cout << "Could not open or find the image" << endl;cin.get();return -1;}Mat imageContrastHigh2;image.convertTo(imageContrastHigh2, -1, 2, 0); //increase the contrast by 2Mat imageContrastHigh4;image.convertTo(imageContrastHigh4, -1, 4, 0); //increase the contrast by 4Mat imageContrastLow0_5;image.convertTo(imageContrastLow0_5, -1, 0.5, 0); //decrease the contrast by 0.5Mat imageContrastLow0_25;image.convertTo(imageContrastLow0_25, -1, 0.25, 0); //decrease the contrast by 0.25//Defining window names for above imagesString windowNameOriginalImage = "Original Image";String windowNameContrastHigh2 = "Contrast Increased by 2";String windowNameContrastHigh4 = "Contrast Increased by 4";String windowNameContrastLow0_5 = "Contrast Decreased by 0.5";String windowNameContrastLow0_25 = "Contrast Decreased by 0.25";//Create and open windows for above imagesnamedWindow(windowNameOriginalImage, WINDOW_NORMAL);namedWindow(windowNameContrastHigh2, WINDOW_NORMAL);namedWindow(windowNameContrastHigh4, WINDOW_NORMAL);namedWindow(windowNameContrastLow0_5, WINDOW_NORMAL);namedWindow(windowNameContrastLow0_25, WINDOW_NORMAL);//Show above images inside the created windows.imshow(windowNameOriginalImage, image);imshow(windowNameContrastHigh2, imageContrastHigh2);imshow(windowNameContrastHigh4, imageContrastHigh4);imshow(windowNameContrastLow0_5, imageContrastLow0_5);imshow(windowNameContrastLow0_25, imageContrastLow0_25);waitKey(0); // Wait for any key strokedestroyAllWindows(); //destroy all open windowsreturn 0; }

Result

Explanation

void Mat::convertTo( OutputArray m, int rtype, double alpha=1, double beta=0 ) const

This function converts the each pixel value to the target data type and changes the value as per the following formula. pixel_value_of_output_image(x, y) = pixel_value_of_input_image(x, y) * alpha + beta;

m - Output image. This data structure will be reallocated if required.

rtype - Type of the output image. If rtype is a negative value, the type of the output image will be same as the input image.

alpha - Each pixels in the input image will be multiplied by this number before assigning to the output image.

beta - This value will be added to each pixels in the input image and assigned to the output image.

轉載于:https://www.cnblogs.com/zdfffg/p/11558241.html

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