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How to adjust the threshold for template matching in openCV (java)?

I am running template matching using openCV 3.4.7 Android SDK (java).
The code work almost perfectly; when the template is match, it draws a rectangle on the matching area. The problem is that even when there is no match, it draws a random rectangle. I think that happens because the threshold is not set correctly. If so, can someone please help me out?
Here's the code:
public static void run(String inFile, String templateFile, String outFile,
int match_method) {
Mat img = Imgcodecs.imread(inFile);
Mat templ = Imgcodecs.imread(templateFile);
// / Create the result matrix
int result_cols = img.cols() - templ.cols() + 1;
int result_rows = img.rows() - templ.rows() + 1;
Mat result = new Mat(result_rows, result_cols, CvType.CV_32FC1);
// / Do the Matching and Normalize
Imgproc.matchTemplate(img, templ, result, match_method);
Core.normalize(result, result, 0, 1, Core.NORM_MINMAX, -1, new Mat());
// / Localizing the best match with minMaxLoc
Core.MinMaxLocResult mmr = Core.minMaxLoc(result);
Point matchLoc;
if (match_method == Imgproc.TM_SQDIFF
|| match_method == Imgproc.TM_SQDIFF_NORMED) {
matchLoc = mmr.minLoc;
} else {
matchLoc = mmr.maxLoc;
}
// / Show me what you got
Imgproc.rectangle(img, matchLoc, new Point(matchLoc.x + templ.cols(),
matchLoc.y + templ.rows()), new Scalar(0, 0, 128));
// Save the visualized detection.
System.out.println("Writing " + outFile);
Imgcodecs.imwrite(outFile, img);
}

You can use Imgproc.TM_CCOEFF_NORMED or Imgproc.TM_CCORR_NORMED and mmr.maxVal >= 0.8. It should take care of most of your false positives.
Sample Code:
import org.opencv.core.*;
import org.opencv.imgcodecs.Imgcodecs;
import org.opencv.imgproc.Imgproc;
import java.io.File;
import java.nio.file.Files;
public class templateMatchingTester {
private static String str = null;
static {
if (str == null) {
str = "initialised";
nu.pattern.OpenCV.loadShared();
System.loadLibrary(Core.NATIVE_LIBRARY_NAME);
}
}
private static Mat createMatrixFromImage(String imagePath) {
Mat imageMatrix = Imgcodecs.imread(imagePath);
Mat greyImage = new Mat();
Imgproc.cvtColor(imageMatrix, greyImage, Imgproc.COLOR_BGR2GRAY);
return greyImage;
}
private static boolean matchTemplate(String pathToInputImage,String pathToTemplate){
Mat inputImage = createMatrixFromImage(pathToInputImage);
Mat templateImage = createMatrixFromImage(pathToTemplate);
// Create the result matrix
int result_cols = inputImage.cols() - templateImage.cols() + 1;
int result_rows = inputImage.rows() - templateImage.rows() + 1;
Mat result = new Mat(result_rows, result_cols, CvType.CV_8UC1);
int match_method;
match_method = Imgproc.TM_CCOEFF_NORMED;//Imgproc.TM_CCORR_NORMED;
Imgproc.matchTemplate(inputImage, templateImage, result, match_method);
Core.MinMaxLocResult mmr = Core.minMaxLoc(result);
double minMatchQuality = 0.85;
System.out.println(mmr.maxVal);
if (mmr.maxVal >= minMatchQuality){
return true;
} else
return false;
}
public static void main(String args[]) {
String template = "path/to/your/templateImage";
final File folder = new File("path/to/your/testImagesFolder/");
int matchCount = 0;
for (final File fileEntry : folder.listFiles()){
if (matchTemplate(fileEntry.getPath(),template)){
matchCount+=1;
}else
System.out.println(fileEntry.getPath());
}
System.out.println(matchCount);
}
}

Use a normed match method to ensure your match value is [0..1].
Replace this line
Core.normalize(result, result, 0, 1, Core.NORM_MINMAX, -1, new Mat());
with a thresholding operation. Otherwise a best match of 0.9 would become 1 by the second normalization and you would lose the actual match "quality" information.
Normalizing the result of the template matching will always result in your best match being 1 making it impossible to discard a bad match.

i wrote an app that would take a screenshot of the game overwatch and attempt to tell who is on each team. using template matching and open cv. project need to iterate over the result image and check values.
OpenCVUtils.getPointsFromMatAboveThreshold(result,
0.90f)
public static void scaleAndCheckAll(String guid){
Mat source = imread(IMG_PROC_PATH + guid); //load the source image
Mat scaledSrc = new Mat(defaultScreenshotSize, source.type());
resize(source, scaledSrc, defaultScreenshotSize);
Mat sourceGrey = new Mat(scaledSrc.size(), CV_8UC1);
cvtColor(scaledSrc, sourceGrey, COLOR_BGR2GRAY);
for (String hero : getCharacters()) {
Mat template = OpenCVUtils.matFromJar(TEMPLATES_FOLDER + hero + ".png", 0); //load a template
Size size = new Size(sourceGrey.cols()-template.cols()+1, sourceGrey.rows()-template.rows()+1);
Mat result = new Mat(size, CV_32FC1);
matchTemplate(sourceGrey, template, result, TM_CCORR_NORMED);// get results
Scalar color = OpenCVUtils.randColor();
List<Point> points = OpenCVUtils.getPointsFromMatAboveThreshold(result,
0.90f);
for (Point point : points) {
//rectangle(scaledSrc, new Rect(point.x(),point.y(),template.cols(),template.rows()), color, -2, 0, 0);
putText(scaledSrc, hero, point, FONT_HERSHEY_PLAIN, 2, color);
}
}
String withExt = IMG_PROC_PATH + guid +".png";
imwrite(withExt, scaledSrc);
File noExt = new File(IMG_PROC_PATH + guid);
File ext = new File(withExt);
noExt.delete();
ext.renameTo(noExt);
}
the other method.
public static List<Point> getPointsFromMatAboveThreshold(Mat m, float t){
List<Point> matches = new ArrayList<Point>();
FloatIndexer indexer = m.createIndexer();
for (int y = 0; y < m.rows(); y++) {
for (int x = 0; x < m.cols(); x++) {
if (indexer.get(y,x)>t) {
System.out.println("(" + x + "," + y +") = "+ indexer.get(y,x));
matches.add(new Point(x, y));
}
}
}
return matches;
}
you can just get the first from the list or see how close they are if you expect multiple matches.

OpenCv matching template in Video [Java]

please i try to make a new application in java for matching picture and video, the matching of template in picture working fine , but when i try to do it for video i always have this error message :
OpenCV Error: Assertion failed ((depth == CV_8U || depth == CV_32F) &&
type == _templ.type() && _img.dims() <= 2) in cv::matchTemplate, file
C:\builds\master_PackSlaveAddon-win64-vc12-static\opencv\modules\imgproc\src\templmatch.cpp,
line 1062 Exception in thread "main" CvException
[org.opencv.core.CvException: cv::Exception:
C:\builds\master_PackSlaveAddon-win64-vc12-static\opencv\modules\imgproc\src\templmatch.cpp:1062:
error: (-215) (depth == CV_8U || depth == CV_32F) && type ==
_templ.type() && _img.dims() <= 2 in function cv::matchTemplate ]
This is my function for matching video with picture , someone can help please .
public int runVedio(String inFile, String templateFile, int match_method) {
int nbr = 0;
Mat templ = Imgcodecs.imread(templateFile);
VideoCapture capture=new VideoCapture(inFile);
Mat frame = new Mat();
Mat result = new Mat();
capture.read(frame);
// / Do the Matching and Normalize
Imgproc.matchTemplate(frame,templ, result, match_method);
Imgproc.threshold(result, result,0.9,1,Imgproc.THRESH_TOZERO);
//Core.normalize(result, result, 0, 1, Core.NORM_MINMAX, -1, new Mat());
while(true)
{
// / Localizing the best match with minMaxLoc
Core.MinMaxLocResult mmr = Core.minMaxLoc(result);
Point matchLoc;
if (match_method == Imgproc.TM_SQDIFF || match_method == Imgproc.TM_SQDIFF_NORMED) {
matchLoc = mmr.minLoc;
} else {
matchLoc = mmr.maxLoc;
}
if(mmr.maxVal > 0.98)
{
// / Show me what you got
Imgproc.rectangle(frame, matchLoc,
new Point(matchLoc.x + templ.cols(),matchLoc.y + templ.rows()),
new Scalar(0,255,0),2);
Imgproc.rectangle(result, matchLoc,
new Point(matchLoc.x + templ.cols(),matchLoc.y + templ.rows()),
new Scalar(0,255,0),-1);
nbr++;
}
else
{
return nbr;
}
}
}

make sure you are accessing the video correctly for that you can use :
while(camera.read(frame))
Since, it's a video you need to access all the frames in it so use while.
And also your result image i.e
Mat result = new Mat();
must go like below, so that both the images are of same size and are of same color code.
So change it to this ,
new Mat(frame.rows(), frame.cols(), Highgui.CV_LOAD_IMAGE_COLOR);
Run the code and tell me weather it works..

Compare Camera captured images with computer generated images

I am making an app which compare camera captured image with computer generated images and these images are stored in database.
I am using Opencv for image comparison but it only compare computer generated images correctly.When i capture same image with camera and compare that image with computer generated image then it does not match them acuurately.Is there any way where i can compare camera images also;
Here is my code
public static void main(String[] args) {
// Set image path
String path = System.getProperty("user.dir");
String filename1 = path+"/images/266.jpg";
String filename2 = path+"/images/20160805_121529.jpg";
int ret;
ret = compareFeature(filename1, filename2);
if (ret > 0) {
System.out.println("Two images are same.");
} else {
System.out.println("Two images are different.");
}
}
/**
* Compare that two images is similar using feature mapping
* #author minikim
* #param filename1 - the first image
* #param filename2 - the second image
* #return integer - count that has the similarity within images
*/
public static int compareFeature(String filename1, String filename2) {
int retVal = 0;
long startTime = System.currentTimeMillis();
System.loadLibrary(Core.NATIVE_LIBRARY_NAME);
// Load images to compare
Mat img1 = Imgcodecs.imread(filename1, Imgcodecs.CV_LOAD_IMAGE_COLOR);
Mat img2 = Imgcodecs.imread(filename2, Imgcodecs.CV_LOAD_IMAGE_COLOR);
// Declare key point of images
MatOfKeyPoint keypoints1 = new MatOfKeyPoint();
MatOfKeyPoint keypoints2 = new MatOfKeyPoint();
Mat descriptors1 = new Mat();
Mat descriptors2 = new Mat();
// Definition of ORB key point detector and descriptor extractors
FeatureDetector detector = FeatureDetector.create(FeatureDetector.ORB);
DescriptorExtractor extractor = DescriptorExtractor.create(DescriptorExtractor.ORB);
// Detect key points
detector.detect(img1, keypoints1);
detector.detect(img2, keypoints2);
// Extract descriptors
extractor.compute(img1, keypoints1, descriptors1);
extractor.compute(img2, keypoints2, descriptors2);
// Definition of descriptor matcher
DescriptorMatcher matcher = DescriptorMatcher.create(DescriptorMatcher.BRUTEFORCE_HAMMING);
// Match points of two images
MatOfDMatch matches = new MatOfDMatch();
// System.out.println("Type of Image1= " + descriptors1.type() + ", Type of Image2= " + descriptors2.type());
// System.out.println("Cols of Image1= " + descriptors1.cols() + ", Cols of Image2= " + descriptors2.cols());
// Avoid to assertion failed
// Assertion failed (type == src2.type() && src1.cols == src2.cols && (type == CV_32F || type == CV_8U)
if (descriptors2.cols() == descriptors1.cols()) {
matcher.match(descriptors1, descriptors2 ,matches);
// Check matches of key points
DMatch[] match = matches.toArray();
double max_dist = 0; double min_dist = 100;
for (int i = 0; i < descriptors1.rows(); i++) {
double dist = match[i].distance;
if( dist < min_dist ) min_dist = dist;
if( dist > max_dist ) max_dist = dist;
}
System.out.println("max_dist=" + max_dist + ", min_dist=" + min_dist);
// Extract good images (distances are under 10)
for (int i = 0; i < descriptors1.rows(); i++) {
if (match[i].distance <= 10) {
retVal++;
}
}
System.out.println("matching count=" + retVal);
}
long estimatedTime = System.currentTimeMillis() - startTime;
System.out.println("estimatedTime=" + estimatedTime + "ms");
return retVal;
}
Here is pictures that i am comparing
And here is camera captured image
Thanks in Advance

template matching with multiple templates in android

I'm a beginner to OpenCV.
I'm trying to do template matching with multiple tempates.
for single template i get the source code from here
OpenCV Template Matching example in Android
I searched in the internet and I couldn't find a proper android or java code which satisfy my requirement.
I have C++ code but I dont know how to translate it.
Can you please help me to find a proper java or android code. Or else please help me with translate this C++ code into java, which I can use inside android application.
Thank you in advance.
C++ code
#include "opencv2/highgui/highgui.hpp"
#include "opencv2/imgproc/imgproc.hpp"
#include <iostream>
#include <stdio.h>
using namespace std;
using namespace cv;
bool FindTemplate(Mat Img_Scene_Bgr,Mat Img_Template_Bgr,Point &Point_TemplateLocation)
{
// `Img_Scene_Bgr` and `Img_Template_Bgr` are the reference and template image
cv::Mat Img_Result_Float(Img_Scene_Bgr.rows-Img_Template_Bgr.rows+1, Img_Scene_Bgr.cols-Img_Template_Bgr.cols+1, CV_32FC1);
cv::matchTemplate(Img_Template_Bgr, Img_Scene_Bgr, Img_Result_Float, CV_TM_CCOEFF_NORMED);
normalisasi normalize( Img_Result_Float, Img_Result_Float, 0, 1, NORM_MINMAX, -1, Mat() );
double minval, maxval, threshold = 0.7;
cv::Point minloc, maxloc;
cv::minMaxLoc(Img_Result_Float, &minval, &maxval, &minloc, &maxloc);
if (maxval >= threshold)
{
Point_TemplateLocation= maxloc;
return true;
}
else
{
return false;
}
}
int main( int argc, char** argv )
{
Mat Img_Scene;
Mat Img_Template_1;
Mat Img_Template_2;
Mat Img_Result;
char* image_window = "Source Image";
char* result_window = "Result window";
/// Load image and template
Img_Scene = imread("SceneImage.png", 1 );
Img_Template_1 = imread( "Templ1.png", 1 );
Img_Template_2 = imread( "Templ2.png", 1 );
if(Img_Scene.data== NULL||Img_Template_1.data==NULL||Img_Template_2.data==NULL)
{
cout<<"Image Not Found";
return 0;
}
Img_Result= Img_Scene.clone();
Vector<Mat> List_Template_Img;
List_Template_Img.push_back(Img_Template_1);//Otherwise Get some folder & add the Files in it
List_Template_Img.push_back(Img_Template_2);
Point Point_TemplateLocation;
for (int i = 0; i < List_Template_Img.size(); i++)
{
if(!FindTemplate(Img_Scene,List_Template_Img[i],Point_TemplateLocation))
{
cout<<"No Match Found";
}
/// Show me what you got
rectangle( Img_Result, Point_TemplateLocation, Point( Point_TemplateLocation.x + Img_Template_1.cols , Point_TemplateLocation.y + Img_Template_1.rows ), Scalar(0,0,255), 2, 8, 0 );
putText( Img_Result, format("Object %d ",i),Point( Point_TemplateLocation.x + Img_Template_1.cols/4 , Point_TemplateLocation.y + Img_Template_1.rows/2 ),1,1,Scalar(255,0,0),1,-1);
}
/// Create windows
namedWindow( image_window, CV_WINDOW_AUTOSIZE );
namedWindow( result_window, CV_WINDOW_AUTOSIZE );
imshow( image_window, Img_Template_1);
imshow( image_window, Img_Template_2);
imshow( result_window, Img_Result );
waitKey(0);
return 0;
}

I tried to write a script like this, but I am confused in the calculation process and bring the results of calculations
public void matching() {
String img_eq = Environment.getExternalStorageDirectory().getAbsolutePath() + "/img_eq/img_eq.jpg";
String template = Environment.getExternalStorageDirectory().getAbsolutePath() + "/img_template/img_template.jpg";
String template2 = Environment.getExternalStorageDirectory().getAbsolutePath() + "/img_template/img_template2.jpg";
Mat img = Highgui.imread(img_eq, CvType.CV_8SC3);
Mat templ = Highgui.imread(template, CvType.CV_8SC3);
Mat templ_2 = Highgui.imread(template2, CvType.CV_8SC3);
int match_method = Imgproc.TM_SQDIFF_NORMED;
int result_cols = img.cols() - templ.cols() + 1;
int result_rows = img.rows() - templ.rows() + 1;
Mat result = new Mat(result_rows, result_cols, CvType.CV_8SC3);
Imgproc.matchTemplate(img, templ, result, match_method);
Core.normalize(result, result, 0, 1, Core.NORM_MINMAX, -1, new Mat());
// / Localizing the best match with minMaxLoc
MinMaxLocResult mmr = Core.minMaxLoc(result);
Point matchLoc = new Point();
//for (int i = 0; i < List_template_image.size(); i++)
{
if (match_method == Imgproc.TM_SQDIFF || match_method == Imgproc.TM_SQDIFF_NORMED) {
matchLoc = mmr.minLoc;
} else {
matchLoc = mmr.maxLoc;
}
// / Show me what you got
Core.rectangle(img, matchLoc, new Point(matchLoc.x + templ.cols(),
matchLoc.y + templ.rows()), new Scalar(0, 255, 0));
// Save the visualized detection.
Highgui.imwrite("/mnt/sdcard/img_result/img_result.jpg", img);
Mat image = Highgui.imread("/mnt/sdcard/img_result/img_result.jpg");
Mat android_image = Mat.zeros(image.cols(), image.rows(), CvType.CV_8SC3);
Imgproc.cvtColor(image, android_image, Imgproc.COLOR_BGR2RGB);
Bitmap bm = Bitmap.createBitmap(android_image.cols(),android_image.rows(), Bitmap.Config.ARGB_8888);
Utils.matToBitmap(android_image, bm);
ImageView iv = (ImageView) findViewById(R.id.image);
iv.setImageBitmap(bm);
}

How to match multiple objects

How do i match multiple objects using a single template?
i want to match multiple objects by threshold value.
When i matched a single object, i used this code.
System.loadLibrary(Core.NATIVE_LIBRARY_NAME);
Mat img = Highgui.imread("/test/test_img.jpg");//input image
if(img.empty())
throw new Exception("no image");
Mat tpl = Highgui.imread("/test/test_tpl.jpg");//template image
if(tpl.empty())
throw new Exception("no template");
Mat result = new Mat();
Imgproc.matchTemplate(img, tpl,result,Imgproc.TM_CCOEFF_NORMED);//Template Matching
Core.MinMaxLocResult maxr = Core.minMaxLoc(result);
Point maxp = maxr.maxLoc;
Point maxop = new Point(maxp.x + tpl.width(), maxp.y + tpl.height());
Mat dst = img.clone();
Core.rectangle(dst, maxp, maxop, new Scalar(255,0,0), 2);//draw a rectangle
Highgui.imwrite("/test/test.jpg", dst);//save image

This one is working for me:
Mat img = Highgui.imread("/test/test_img.jpg");//input image
if(img.empty())
throw new Exception("no image");
Mat tpl = Highgui.imread("/test/test_tpl.jpg");//template image
if(tpl.empty())
throw new Exception("no template");
Mat result = new Mat();
Imgproc.matchTemplate(img, tpl,result,Imgproc.TM_CCOEFF_NORMED);//Template Matching
Imgproc.threshold(result, result, 0.1, 1, Imgproc.THRESH_TOZERO);
double threshold = 0.95;
double maxval;
Mat dst;
while(true)
{
Core.MinMaxLocResult maxr = Core.minMaxLoc(result);
Point maxp = maxr.maxLoc;
maxval = maxr.maxVal;
Point maxop = new Point(maxp.x + tpl.width(), maxp.y + tpl.height());
dst = img.clone();
if(maxval >= threshold)
{
System.out.println("Template Matches with input image");
Core.rectangle(img, maxp, new Point(maxp.x + tpl.cols(),
maxp.y + tpl.rows()), new Scalar(0, 255, 0),5);
Core.rectangle(result, maxp, new Point(maxp.x + tpl.cols(),
maxp.y + tpl.rows()), new Scalar(0, 255, 0),-1);
}else{
break;
}
}
Highgui.imwrite("test.jpg", dst);//save image
for example
the template:
coin
and the result:
marioWorld