iOS: OpenCV Red color range - ios

Question

I am trying to encircle Red color in the picture using OpenCV library. I have seen many question in google but no one helped for me. My code is below:
void highLightRed(const cv::Mat& inputFrame, cv::Mat& outputFrame)
{
cv::Mat gray, edges, red, blurred;
// blur will enhance edge detection
medianBlur(inputFrame, blurred, 9);
// give image in gray color space
getGray(blurred, gray);
cv::inRange(gray, cv::Scalar(0,0,112), cv::Scalar(60,0,225), red); //BGR
// using Canny algorithm to find edges
cv::Canny(red, edges, 50, 150);
std::vector< std::vector<cv::Point> > c;
// find contours of edges
cv::findContours(edges, c, cv::RETR_EXTERNAL, cv::CHAIN_APPROX_NONE);
NSLog(#"size: %lu", c.size());
inputFrame.copyTo(outputFrame);
// draw contour in green (0,200,0) with thinkness 3
//cv::drawContours(outputFrame, c, -1, cv::Scalar(0,200,0),3);
cv::drawContours(outputFrame, c, -1, cv::Scalar(0,200,0),2);
}
void getGray(const cv::Mat& input, cv::Mat& gray)
{
const int numChannes = input.channels();
if (numChannes == 4)
{
cv::cvtColor(input, gray, cv::COLOR_BGRA2GRAY);
}
}
Problem: This code works perfect if only Red and white color are there in picture, it encircles red color successfully. But if multiple colors specially dark colors are involved the color detection fails.
I need exact range which only detect Red color. Thanks

Answer 1

Finding the exact range of color in BGR or RGB format is very difficult. You will have to play around it a lot (if you are a newbie).
A very simple way:
Convert your image into HSV format using cvtColor()
Split your HSV image into three channel i.e. H, S and V-channel.
Extract the red color from the H-channel. You can have a look here to find the hue range of Red color.
Merge this new H-channel with the old S and V channel.
Convert back to BGR format. Now your BGR image will contain only the Red color.