How to set mask image for grabCut in OpenCV?

Question

How to set mask image for grabCut function in OpenCV? I want to do GC_INIT_WITH_MASK with parameters

GC_BGD = 0, GC_FGD = 1, GC_PR_BGD = 2, GC_PR_FGD = 3, 

If you can answer this with JavaCV, it would be great as I do this in Scala / Java.

Answer 1

Working example in OpenCV:

 //Fill with the background value Mat mask = cv::Mat::ones(src.size(), CV_8U) * cv::GC_BGD; //Fill a smaller rectangle with the probably-foreground value. Rect area; area.x=10; area.y=10; area.width=250; area.height=250; rectangle(mask, area , cv::Scalar(cv::GC_PR_FGD),-1,8,0); //Fill a smaller rectangle with the foreground value. area.x=50; area.y=50; area.width=20; area.height=20; rectangle(mask, area , cv::Scalar(cv::GC_FGD),-1,8,0); Mat bgd,fgd; cv::grabCut(src, mask, area, bgd, fgd, 1, cv::GC_INIT_WITH_MASK); //Visualize results. compare(mask,cv::GC_FGD,mask,cv::CMP_EQ); Mat foreground(src.size(),CV_8UC3, cv::Scalar(0,0,0)); src.copyTo(foreground,mask); imshow("segm",foreground); 

Answer 2

 public class ImageSegment { public static void main(String[] args) { System.loadLibrary("opencv_java244"); Mat image = null; image = Highgui.imread("syh.jpg"); Rect rectangle = new Rect(25,25,image.cols()-64,image.rows()-64); Mat result = new Mat(); Mat bgdModel = new Mat(); Mat fgdModel = new Mat(); Mat source = new Mat(1, 1, CvType.CV_8U, new Scalar(3)); Imgproc.grabCut(image, result, rectangle, bgdModel, fgdModel, 1, 0); Core.compare(result, source,result, Core.CMP_EQ); Mat foreground= new Mat(image.size(), CvType.CV_8UC1, new Scalar(0, 0, 0)); image.copyTo(foreground, result); Highgui.imwrite("sucess1.jpg", foreground); System.out.println("grabcut sucess!"); } } 

Answer 3

Input Images (lena.png, lena_mask.png):

Code (JAVA) :

 import org.opencv.core.Core; import org.opencv.core.CvType; import org.opencv.core.Mat; import org.opencv.core.Rect; import org.opencv.core.Scalar; import org.opencv.highgui.Highgui; import org.opencv.imgproc.Imgproc; /** * Example how to use grabCut algorithm in OpenCV using GC_INIT_WITH_MASK. * */ public class ImageSegmentByMask { public static void main(String[] args) { System.loadLibrary(Core.NATIVE_LIBRARY_NAME); // will read image Mat image = Highgui.imread("lena.png"); Mat mask = Highgui.imread("lena_mask.png", Highgui.CV_LOAD_IMAGE_GRAYSCALE); Rect rectangle = new Rect(10, 10, image.cols() - 20, image.rows() - 20); Mat bgdModel = new Mat(); // extracted features for background Mat fgdModel = new Mat(); // extracted features for foreground Mat source = new Mat(1, 1, CvType.CV_8U, new Scalar(0)); convertToOpencvValues(mask); // from human readable values to OpenCV values int iterCount = 1; Imgproc.grabCut(image, mask, rectangle, bgdModel, fgdModel, iterCount, Imgproc.GC_INIT_WITH_MASK); convertToHumanValues(mask); // back to human readable values Imgproc.threshold(mask,mask,128,255,Imgproc.THRESH_TOZERO); Mat foreground = new Mat(image.size(), CvType.CV_8UC1, new Scalar(0, 0, 0)); image.copyTo(foreground, mask); Highgui.imwrite("sandbox/sucess1.jpg", foreground); } private static void convertToHumanValues(Mat mask) { byte[] buffer = new byte[3]; for (int x = 0; x < mask.rows(); x++) { for (int y = 0; y < mask.cols(); y++) { mask.get(x, y, buffer); int value = buffer[0]; if (value == Imgproc.GC_BGD) { buffer[0] = 0; // for sure background } else if (value == Imgproc.GC_PR_BGD) { buffer[0] = 85; // probably background } else if (value == Imgproc.GC_PR_FGD) { buffer[0] = (byte) 170; // probably foreground } else { buffer[0] = (byte) 255; // for sure foreground } mask.put(x, y, buffer); } } } /** * Converts level of grayscale into OpenCV values. White - foreground, Black * - background. * * @param mask */ private static void convertToOpencvValues(Mat mask) { byte[] buffer = new byte[3]; for (int x = 0; x < mask.rows(); x++) { for (int y = 0; y < mask.cols(); y++) { mask.get(x, y, buffer); int value = buffer[0]; if (value >= 0 && value < 64) { buffer[0] = Imgproc.GC_BGD; // for sure background } else if (value >= 64 && value < 128) { buffer[0] = Imgproc.GC_PR_BGD; // probably background } else if (value >= 128 && value < 192) { buffer[0] = Imgproc.GC_PR_FGD; // probably foreground } else { buffer[0] = Imgproc.GC_FGD; // for sure foreground } mask.put(x, y, buffer); } } } } 

Result

Answer 4

The source image mask is the second argument to grabCut , so you just need to create an image with CvMat.create() , and then set the values GC_BGD, GC_FGC, GC_PR_BGD, GC_PR_FGD (unable to check the code for this computer), respectively:

 val mask = cvCreateImage(cvGetSize(image), IPL_DEPTH_8U, 1) // Set mask pixel values to what you want mask.put(offset, GC_BGD) ... grabCut(image, mask, ... <your other options here>) 

I'm not the most familiar with javacv, maybe a good way to set values ​​in ranges or blocks for a mask instead of one pixel at a time.

Also according to docs for grabCut :

"Note that GC_INIT_WITH_RECT and GC_INIT_WITH_MASK can be combined, then all pixels outside the ROI are automatically initialized with GC_BGD"