add gaussian noise to colour image

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And what have you tried?

I have tried to separate the colour channels and add noise to each of them and merge them. And succeed to do so. But I want to separate the Y Cr Cb components and then add noise to only Y. Finally merge the components but could not. My code for colour channels:

for (int i=0;i<3;i++) {

    Mat noise = Mat(channel[i].size(),CV_64F);

    normalize(channel[i], result[i], 0.0, 1.0, CV_MINMAX, CV_64F);
    randn(noise, 0, .2);
    result[i] = result[i] + noise;
    normalize(result[i], result[i], 0.0, 1.0, CV_MINMAX, CV_64F);

    result[i].convertTo(result[i], CV_32F, 255, 0);
        }


merge(result,3,input);
imwrite("/Users/hossainmdshakhawat/developer/subimg/Noisy/merge.jpg",input);

And why can't you add noise just to channel Y? Are you getting any errors or what?

I can split the Y Cr, and Cb. I can add noise to Y too. But while I am trying to merge I am getting assertion error.

which assertion error? and with which exact code? Please, provide all the relevant information, we can't imagine things...

my code:

Mat ycrcb = input.clone(); cvtColor(input, ycrcb, CV_BGR2YCrCb);

Mat channel[3];
Mat result[3];

split(ycrcb,channel);

    Mat noise = Mat(channel[0].size(),CV_64F);


    normalize(channel[0], result[0], 0.0, 1.0, CV_MINMAX, CV_64F);
    randn(noise, 0, .1);
    result[0] = result[0] + noise;
    normalize(result[0], result[0], 0.0, 1.0, CV_MINMAX, CV_64F);

    result[0].convertTo(channel[0], CV_32F, 255, 0);

    imwrite("gaussiannoisy.jpg",channel[0]);

Mat output;
merge(channel,3,output);

imwrite("merge.jpg",output);

This is the error OpenCV Error: Assertion failed (mv[i].size == mv[0].size && mv[i].depth() == depth) in merge, file /Users/hossainmdshakhawat/opencv-3.0.0/modules/core/src/convert.cpp, line 950 libc++abi.dylib: terminating with uncaught exception of type cv::Exception: /Users/hossainmdshakhawat/opencv-3.0.0/modules/core/src/convert.cpp:950: error: (-215) mv[i].size == mv[0].size && mv[i].depth() == depth in function merge

Please suggest is there any better and simple way to add noise to colour with varying std of gaussian noise.

You're modifying Y channel and converting it to CV_32F, but your Cr and Cb channels are still CV_8U. Therefore, you can't merge them (all of them have to have the same depth).

Thanks it fixed the error but the resulting noisy image is some how different. It is a yellowish image. And this is not my desired target. Is my way is wrong ? I am very new at opencv and image processing