OpenCV |动手做图像对比

对比度是指更改每个图像像素的值。可以通过将图像的像素值乘以或除以任何常数来完成此更改。本文深入介绍了如何使用OpenCV更改图像对比度。

Input : 
Original Image

Output : 
-> Original Image
-> Image with contrast increased by 4
-> Image with contrast increased by 2
-> Image with contrast decreased by .5
-> Image with contrast decreased by .25

代码：CPP代码，用于增加或减少图像的对比度

CPP

// c++ code explaining how to
// increase or decrease the
// contrast of an image
 
// loading library files
#include 
#include 
#include 
 
using namespace cv;
using namespace std;
 
int main(int argc, char** argv)
{
    // Loading the Image File under testing
    Mat image = imread("C:\\Users\\dell\\Desktop\\abc.jpg");
 
    // Check whether the image is present or not
    if (image.empty()) {
        cout << "Could not open or find the image" << endl;
 
        // waiting for any  key to be pressed
        return -1;
    }
 
    // Declaring the Contrast instances
 
    // increasing the contrast level by 100%
    Mat imageContrastHigh2;
    image.convertTo(imageContrastHigh2, -1, 2, 0);
 
    // increasing the contrast level by 200%
    Mat imageContrastHigh4;
    image.convertTo(imageContrastHigh4, -1, 4, 0);
 
    // decreasing the contrast level by 50%
    Mat imageContrastLow0_5;
    image.convertTo(imageContrastLow0_5, -1, 0.5, 0);
 
    // decreasing the contrast level by 75%
    Mat imageContrastLow0_25;
    image.convertTo(imageContrastLow0_25, -1, 0.25, 0);
 
    // Declaring the windows
    // for images belonging to different contrast level
    String 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";
 
    // Running the window instance
    // and opening it
    namedWindow(windowNameOriginalImage, WINDOW_NORMAL);
    namedWindow(windowNameContrastHigh2, WINDOW_NORMAL);
    namedWindow(windowNameContrastHigh4, WINDOW_NORMAL);
    namedWindow(windowNameContrastLow0_5, WINDOW_NORMAL);
    namedWindow(windowNameContrastLow0_25, WINDOW_NORMAL);
 
    // Loading images inside the above created Windows
    imshow(windowNameOriginalImage, image);
    imshow(windowNameContrastHigh2, imageContrastHigh2);
    imshow(windowNameContrastHigh4, imageContrastHigh4);
    imshow(windowNameContrastLow0_5, imageContrastLow0_5);
    imshow(windowNameContrastLow0_25, imageContrastLow0_25);
 
    // waiting for any key to be pressed
    waitKey(0);
 
    // closing all the windows instances
    // when any key is pressed.
    destroyAllWindows();
 
    return 0;
}

输入 ：

输出 ：
对比度提高了4的图像

对比度提高2倍的图像

对比度降低了0.5的图像

对比度降低了.25的图像

解释 ：

CPP

// Declaring the Contrast instances
 
// increasing the contrast level by 100%
Mat imageContrastHigh2;
image.convertTo(imageContrastHigh2, -1, 2, 0);
 
// increasing the contrast level by 200%
Mat imageContrastHigh4;
image.convertTo(imageContrastHigh4, -1, 4, 0);
 
// decreasing the contrast level by 50%
Mat imageContrastLow0_5;
image.convertTo(imageContrastLow0_5, -1, 0.5, 0);
 
// decreasing the contrast level by 75%
Mat imageContrastLow0_25;
image.convertTo(imageContrastLow0_25, -1, 0.25, 0);

这些代码行会将图像像素值更改指定的数量。然后将最终更改的图像存储到给定的输出图像。如果指定的数量因子大于1，则对比度级别将增加；否则，如果指定的数量因子小于1，则对比度级别将降低。
MAT函数：
“ MAT”函数将每个图像像素值更改为目标数据类型，并且值会随着倍数的倍增而变化。

Parameters : 

m      : Output Image 
rtype  : Output Image type, Output Image type is same
        as input if it is set to -ve value
alpha  : Input image pixel are multiplied with this
        number prior to its assignment to output image
beta   : adding this value to each input image pixel 

要从最佳影片策划和实践问题去学习，检查了C++基础课程为基础，以先进的C++和C++ STL课程基础加上STL。要完成从学习语言到DS Algo等的更多准备工作，请参阅“完整面试准备课程” 。