create a random colour image in OpenCV - c++

Question

I am new to OpenCV. I am trying to create a random color image. Firstly I tried to create a random grayscale image. The code I have attached below
void random_colour(Mat input_image) {
for (int i = 0; i < image.rows; i++)
for (int j = 0; j < image.cols; j++)
image.at<uchar>(i,j)= rand()%255;
imwrite("output.tif",image);
}
int main( int argc, char** argv )
{
Mat img=Mat::zeros(100,100,CV_8UC1);
random_colour(img);
waitKey(0);
return 0;
}
The output obtained is
Now I changed my above code to create a random colour image as.
void random_colour(Mat input_image) {
for (int i = 0; i < image.rows; i++)
{
for (int j = 0; j < image.cols; j++)
{
image.at<Vec3b>(i,j)[0] = rand()%255;
image.at<Vec3b>(i,j)[1] = rand()%255;
image.at<Vec3b>(i,j)[2] = rand()%255;
}
}
imwrite("output.tif",image);
}
The main function remains same. While doing so, I get a runtime error. Please help me on what should I do. What I understood is that each pixel in colour space has three component RGB. So therefore I am changing all the three component of each pixel. I am not getting the output what I wanted.

Answer 1

no need to reinvent the wheel, please use cv::randu()
#include "opencv2/core.hpp"
#include "opencv2/imgproc.hpp"
#include "opencv2/highgui.hpp"
using namespace cv;
int main(int argc, char** argv)
{
Mat img(100, 100, CV_8UC3);
randu(img, Scalar(0, 0, 0), Scalar(255, 255, 255));
imshow("random colors image", img);
waitKey();
return 0;
}

Answer 2

This line creates a greyscale image, it doesn't have three channels.
Mat img=Mat::zeros(100,100,CV_8UC1);
That means when you use this line, its going to crash:
image.at<Vec3b>(i,j)[0] = rand()%255;
You need to not use CV_8UC1 because that creates 1 channel (C1) try it with CV_8UC3 instead
Mat img=Mat::zeros(100,100,CV_8UC3);
FYI 8u means 8 bit so values 0 to 255, CX is the number of channels in the image. If you want BGR you need C3.