CODEWITHSUNDEEP
opencv
preeti
preeti

Reputation: 1

Convert color image into grey in opencv without CV_RGB2GRAY

I want to convert colorBGR image into grey scale in opencv without using direct command CV_RGB2GRAY. Here I uploaded my code which gives me a bluish color of the image which is not a proper grey output image. Please check the below code and tell me where I m going wrong or you can give me another solution to convert the color image into grey output image without CV_RGB2GRAY. Thanks in advance.

Mat image=imread("Desktop\\Sample input\\ip1.png");
Mat grey( image.rows,image.cols, CV_8UC3);
for(int i=0;i<image.rows;i++)
        {
            for(int j=0;j<image.cols;j++)
            {
                 int blue = image.at<Vec3b>(i,j)[0];
                 int green = image.at<Vec3b>(i,j)[1];
                 int red = image.at<Vec3b>(i,j)[2];

                grey.at<Vec3b>(i,j) = 0.114*blue+0.587*green+ 0.299*red ;   
            }
        }
  imshow("grey image",grey);

Upvotes: 0

Views: 686

Answers (2)

Saif Mahmud Parvez
Saif Mahmud Parvez

Reputation: 77

If you intend to convert the image which you are taking by imread() functions, you can take the image as input as a grayscale image directly by

Mat image = imread("Desktop\\Sample input\\ip1.png",CV_LOAD_IMAGE_GRAYSCALE);

or, by 

Mat image = imread("Desktop\\Sample input\\ip1.png",0);

It is because CV_LOAD_IMAGE_GRAYSCALE corresponds to the constant 0. And when in imread() function gets this argument zero, it will load an image with intensity one. And if want to convert any image to grayscale then the out image image should like

Mat grey = Mat::zeros(src_image.rows, src_image.cols, CV_8UC1);

as grayscale image is of only one channel and then you can convert the image like this:

for(int i=0;i<image.rows;i++)
        {

            for(int j=0;j<image.cols;j++)
            {
                 int blue = image.at<Vec3b>(i,j)[0];
                 int green = image.at<Vec3b>(i,j)[1];
                 int red = image.at<Vec3b>(i,j)[2];

                grey.at<uchar>(i, j) = (uchar) (0.114*blue + 0.587*green + 0.299*red);   
            }
        }

It will give you the grayscale image.

Upvotes: 3

Ove
Ove

Reputation: 6317

In your code, the grey Mat has 3 channels. For a grayscale image you only need 1 channel (8UC1).

Also, when you are writing the values in the grayscale image, you need to use uchar instead of Vec3b because each pixel in the grayscale image is only made up of one unsigned char value, not a vector of 3 values.

So, you need to replace these lines:

Mat grey(image.rows, image.cols, CV_8UC1);

and

grey.at<uchar>(i, j) = 0.114*blue + 0.587*green + 0.299*red;

Upvotes: 1

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