openCV inRange masking - opencv

Question

I'm using Opencv 3.0 to get only the colored objects in an image. Therefore i create and use a mask.
#include <opencv2\opencv.hpp>
using namespace cv;
using namespace std;
int main()
{
namedWindow("Display", CV_WINDOW_AUTOSIZE);
namedWindow("Orignial", CV_WINDOW_AUTOSIZE);
namedWindow("Mask", CV_WINDOW_AUTOSIZE);
// First load your image
Mat mSrc = imread("IMG_0005_AUSZUG2.png", CV_LOAD_IMAGE_COLOR);
Mat mGray = Mat::zeros(mSrc.size(), mSrc.type());
cvtColor(mSrc, mGray, CV_BGR2GRAY);
// define your mask
Mat mask = Mat::zeros(mSrc.size(), mSrc.type());
// define destination image
Mat dstImg = Mat::zeros(mSrc.size(), mSrc.type());
//finding mask
inRange(mSrc, Scalar(90, 90, 90), Scalar(180, 180, 180), mask);
// combination of mask and Source image
dilate(mask, mask, Mat(), Point(-1, -1));
bitwise_not(mask, mask);
//cvtColor(mask, mask, CV_GRAY2BGR);
mSrc.copyTo(dstImg, mask);
//bitwise_and(mSrc, mSrc, dstImg, mask);
imshow("Mask", mask);
imshow("Orignial", mSrc);
imshow("Display", dstImg);
waitKey(0);
return 0;
}
As you can see the result image is not the intended one. Only the colored objects should stay, because they have a white background in the mask, but it seems that the result image is a combination of source and mask.
Anybody know how to fix this ?
Source:
Mask:
Result:

Answer 1

To understand your requirement- you have an image with some coloured objects in it, in a white background, and you essentially want an result image containing the same coloured objects in a black background instead.
If that's the case, inRange will not help because you've essentially kept the threshold between grey values 90 and 180, so your code will discard dark objects as well.
To ensure that you obtain a mask that is black only in the white background regions, I would suggest using the threshold function instead, as shown:
//finding mask
//inRange(mSrc, Scalar(90, 90, 90), Scalar(180, 180, 180), mask);
threshold(mGray, mask, 220, 255, THRESH_BINARY_INV);
This function will ensure that any pixel value in your greyscale image above 220 will be set to 0 in the binary mask.
To superimpose the binary mask over the source image, you should use the subtract method, as shown:
cvtColor(mask,mask,CV_GRAY2BGR);//change thresh to a 3 channel image
Mat mResult = Mat::zeros(mSrc.size(), mSrc.type());
subtract(mask,mSrc,mResult);
subtract(mask,mResult,mResult);