OpenCV Tutorials —— Changing the contrast and brightness of an image

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Brightness and contrast adjustments

• Two commonly used point processes are multiplication and addition with a constant:

  

 

• The parameters and are often called the gain and bias parameters; sometimes these parameters are said to control contrast and brightness respectively.

 

• You can think of as the source image pixels and as the output image pixels. Then, more conveniently we can write the expression as:

  

  where and indicates that the pixel is located in the i-th row and j-th column.

 

亮度增强

#include "stdafx.h"

#include <cv.h>
#include <highgui.h>
#include <iostream>

using namespace cv;

double alpha; /**< Simple contrast control */
int beta;  /**< Simple brightness control */

int main( int argc, char** argv )
{
	/// Read image given by user
	Mat image = imread( "xue.jpg" );
	Mat new_image = Mat::zeros( image.size(), image.type() );

	/// Initialize values
	std::cout<<" Basic Linear Transforms "<<std::endl;
	std::cout<<"-------------------------"<<std::endl;
	std::cout<<"* Enter the alpha value [1.0-3.0]: ";std::cin>>alpha;
	std::cout<<"* Enter the beta value [0-100]: "; std::cin>>beta;

	/// Do the operation new_image(i,j) = alpha*image(i,j) + beta
	for( int y = 0; y < image.rows; y++ )
	{ for( int x = 0; x < image.cols; x++ )
	{ for( int c = 0; c < 3; c++ )
	{
		new_image.at<Vec3b>(y,x)[c] =
			saturate_cast<uchar>( alpha*( image.at<Vec3b>(y,x)[c] ) + beta );
	}
	}
	}

	/// Create Windows
	namedWindow("Original Image", 1);
	namedWindow("New Image", 1);

	/// Show stuff
	imshow("Original Image", image);
	imshow("New Image", new_image);

	/// Wait until user press some key
	waitKey();
	return 0;
}

new_image.at<Vec3b>(y,x)[c] =
saturate_cast<uchar>( alpha*( image.at<Vec3b>(y,x)[c] ) + beta ); 

注意 ： y，x

注意： image.at<Vec3b>(y,x)[c]

To access each pixel in the images we are using this syntax: image.at<Vec3b>(y,x)[c] where y is the row, x is the column and c is R, G or B (0, 1 or 2).

最后，这样的方法OpenCV有现成的

image.convertTo(new_image, -1, alpha, beta);

OpenCV Tutorials —— Changing the contrast and brightness of an image

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原文地址：http://www.cnblogs.com/sprint1989/p/4101826.html