How to add Noise to Color Image - Opencv

Question

I\'m trying to to add noise to an Image & then Denoise it to test my DeNoising algorithm! So for benchmark i\'m referring this Online Test samples. I\'m trying to replic

Answer 1

There are mainly two methods to add say awgn noise (mean = 0, standard deviation = 30) to a colored image.

First: You can add the awgn noise of mean = 0, standard deviation = 30 to each of Red, Green, and Blue channels independently (or any other color model-HSI, YUV, Lab); and then combine the noisy channels to form the colored noisy image.

Second: To use the in-built function to add noise to the colored image directly. eg. imnoise() in Matlab.

I tried with both the methods (imnoise and independently), I got the same result.

Answer 2

Thank you @Andrey Smorodov For your insights! I got it working! Here is my updated code for adding Noise in a Color Image. Hope this will be useful for someone!

#include "opencv2/imgproc/imgproc.hpp"
#include "opencv2/highgui/highgui.hpp"

#include <iostream>

using namespace cv;
using namespace std;

inline BYTE Clamp(int n)
{
    n = n>255 ? 255 : n;
    return n<0 ? 0 : n;
}

bool AddGaussianNoise(const Mat mSrc, Mat &mDst,double Mean=0.0, double StdDev=10.0)
{
    if(mSrc.empty())
    {
        cout<<"[Error]! Input Image Empty!";
        return 0;
    }

    Mat mGaussian_noise = Mat(mSrc.size(),CV_16SC3);
    randn(mGaussian_noise,Scalar::all(Mean),Scalar::all(StdDev));

    for (int Rows = 0; Rows < mSrc.rows; Rows++)
    {
        for (int Cols = 0; Cols < mSrc.cols; Cols++)
        {
            Vec3b Source_Pixel= mSrc.at<Vec3b>(Rows,Cols);
            Vec3b &Des_Pixel= mDst.at<Vec3b>(Rows,Cols);
            Vec3s Noise_Pixel= mGaussian_noise.at<Vec3s>(Rows,Cols);

            for (int i = 0; i < 3; i++)
            {
                int Dest_Pixel= Source_Pixel.val[i] + Noise_Pixel.val[i];
                Des_Pixel.val[i]= Clamp(Dest_Pixel);
            }
        }
    }

    return true;
}

bool AddGaussianNoise_Opencv(const Mat mSrc, Mat &mDst,double Mean=0.0, double StdDev=10.0)
{
    if(mSrc.empty())
    {
        cout<<"[Error]! Input Image Empty!";
        return 0;
    }
    Mat mSrc_16SC;
    Mat mGaussian_noise = Mat(mSrc.size(),CV_16SC3);
    randn(mGaussian_noise,Scalar::all(Mean), Scalar::all(StdDev));

    mSrc.convertTo(mSrc_16SC,CV_16SC3);
    addWeighted(mSrc_16SC, 1.0, mGaussian_noise, 1.0, 0.0, mSrc_16SC);
    mSrc_16SC.convertTo(mDst,mSrc.type());

    return true;
}


int main(int argc, const char* argv[])
{
    Mat mSource= imread("input.png",1); 
    imshow("Source Image",mSource);

    Mat mColorNoise(mSource.size(),mSource.type());

    AddGaussianNoise(mSource,mColorNoise,0,10.0);

    imshow("Source + Color Noise",mColorNoise); 


    AddGaussianNoise_Opencv(mSource,mColorNoise,0,10.0);//I recommend to use this way!

    imshow("Source + Color Noise OpenCV",mColorNoise);  

    waitKey();
    return 0;
}  

Answer 3

You mentioned "I have tried to add the noise only in the color channel. Convert the Input image into YUV Color space Add the Noise only in the UV Color Channels & Keep the Y channel unaltered."

If you are using the YUV color model, I would suggest you do the opposite. Keep U, and V channel unaltered and add noise only to the Y channel only.

Answer 4

Looks like your noise matrix can't get negative values as it have unsigned char element type. Try operate with real valued matrices, it should help.