Question

I want to do background subtraction in a video file using OpenCV method. Right now I’m able to do background subtraction, but the problem is that I couldn’t get the output in color mode. All the output after subtracting the background is coming in grayscale color mode 🙁. I want to get the color information to the foreground which is the resulting output after background got subtracted.

Can I do it using masking technique?? like the following procedure which I’m thinking about.

1. Capture Input — InputFrame (RGB)
2. Process InputFrame
3. Subtract background, store foreground in TempFrame (which is coming in grayscale 🙁 )
4. Create a mask using TempFrame
5. Apply the created mask to the InputFrame
6. Get colored foreground as OutFrame

I’m struck up with doing the masking using OpenCV. I’m just a very beginner in OpenCV. Please help me to overcome this.

Thanks in advance.

Answer 1

Okay, I don’t understand how TempFrame (your foreground) could be greyscale if you are using background subtraction. You must be using a very special algorithm. But assuming TempFrame is greyscale, then you would do this:

cv::Mat mask = tempFrame > 0.5;

cv::Mat outFrame;
capturedFrame.copyTo(outFrame, mask);

That is OpenCV 2.0 code above. The number 0.5 is a threshold, you’ll need to set it to something appropriate. If you’re not using floating-point images, you’d probably set it to 128 or something like that. This is the same thing in OpenCV 1.1 code:

CvMat* mask = cvCreateMat(tempFrame.rows, tempFrame.cols, CV_8UC1);
cvCmpS(tempFrame, 0.5, mask);

CvMat* outFrame = cvCreateMat(capturedFrame.rows, capturedFrames.cols, CV_32FC3);
cvCopy(capturedFrame, outFrame, mask);