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Articles by Maruthi Krishna
Page 38 of 50
How to draw a polygon in OpenCV using Java?
A polygon with all the interior angles less than 180 is known as a convex polygon. The org.opencv.imgproc package of Java OpenCV library contains a class named Imgproc. To draw a polygon you need to invoke the fillConvexPoly() method of this class. This method accepts 3 parameters −A Mat object representing the image on which the polygon is to be drawn.A MatOfPoint object points between which the polygon is to be drawn.A Scalar object representing the color of the polygon.Exampleimport org.opencv.core.Core; import org.opencv.core.Mat; import org.opencv.core.MatOfPoint; import org.opencv.core.Point; import org.opencv.core.Scalar; import org.opencv.highgui.HighGui; import org.opencv.imgcodecs.Imgcodecs; import org.opencv.imgproc.Imgproc; public class DrawingConvexPolygon { public ...
Read MoreHow to draw a filled circle in OpenCV using Java?
The org.opencv.imgproc package of Java OpenCV library contains a class named Imgproc. This class provides a method named circle(), using this you can draw a circle on an image. This method provides the following parameters −A Mat object representing the image on which the circle is to be drawn.A Point object representing the center of the circle.An integer variable representing the radius of the circle.A Scalar object representing the color of the circle(BGR).An integer representing the thickness of the circle(default 1).If you pass Imgproc.FILLEDas line type, this method generates/draws a filled circle.Exampleimport org.opencv.core.Core; import org.opencv.core.Mat; import org.opencv.core.Point; import org.opencv.core.Scalar; import ...
Read MoreHow to convert OpenCV Mat object to JavaFX WritableImage?
If you try to read an image using the OpenCV imread() method it returns a Mat object. If you want to display the contents of the resultant Mat object using a JavaFX window You need to convert the Mat object to an object of the class javafx.scene.image.WritableImage. To do so, you need to follow the steps given below −Encode the Mat to MatOfByte − First of all, you need to convert the matrix to the matrix of a byte. You can do it using the method imencode() of the class Imgcodecs.This method accepts a String parameter(specifying the image format), a ...
Read MoreHow to create a database in MongoDB using Java?
There is no separate method to create a MongoDB database in Java, you can create a database by invoking the getDatabase() method of the com.mongodb.MongoClient class.Exampleimport com.mongodb.MongoClient; public class CreatingDatabase { public static void main( String args[] ) { //Creating a MongoDB client @SuppressWarnings("resource") MongoClient mongo = new MongoClient( "localhost" , 27017 ); //Accessing the database mongo.getDatabase("myDatabase1"); mongo.getDatabase("myDatabase2"); mongo.getDatabase("myDatabase3"); System.out.println("Databases created successfully"); } }OutputDatabases created successfully
Read MoreHow to drop an index in MongoDB using Java?
In MongoDB to drop an index, you need to use dropIndex() method.Syntaxdb.COLLECTION_NAME.dropIndex({KEY:1})In Java, you can drop an Index using the dropIndex() method, to this method you need to pass the type of the index (ascending or descending) and the field name on which you have created it.dropIndex(Indexes.ascending("name"));Exampleimport com.mongodb.client.MongoCollection; import com.mongodb.client.MongoDatabase; import com.mongodb.client.model.Indexes; import org.bson.Document; import com.mongodb.MongoClient; public class DroppingIndex { public static void main( String args[] ) { //Creating a MongoDB client MongoClient mongo = new MongoClient( "localhost" , 27017 ); //Accessing the database MongoDatabase database = ...
Read MoreExplain Java MongoDB projections
While retrieving data from MongoDb collections you can select only necessary data using projections. In Java, you can project necessary data while reading the documents from a collection using the projection() method. Invoke this method on the result of find(), bypassing the names of the required filed names as −projection(Projections.include("name", "age"));ExampleFollowing Java examples read the documents from a collection, using projection we are displaying the values of name and age fields only.import com.mongodb.client.FindIterable; import com.mongodb.client.MongoCollection; import com.mongodb.client.MongoDatabase; import com.mongodb.client.model.Projections; import java.util.ArrayList; import java.util.Iterator; import java.util.List; import org.bson.Document; import com.mongodb.MongoClient; public class ProjectionExample { public static void main( String args[] ...
Read MoreHow to display OpenCV Mat object using Swings?
The class ImageIcon is an implementation of the Icon interface that paints Icons from Images. You can display images on a Swing window using this class, the constructor of this class accepts a BufferedImage object as a parameter.Therefore to display an OpenCV image that is stored in a Mat object using Swing window, you need to convert it into a BufferedImage object and pass it as a parameter to the ImageIcon method.Exampleimport java.awt.image.BufferedImage; import java.io.ByteArrayInputStream; import java.io.InputStream; import javax.imageio.ImageIO; import javax.swing.ImageIcon; import javax.swing.JFrame; import javax.swing.JLabel; import org.opencv.core.Core; import org.opencv.core.Mat; import org.opencv.core.MatOfByte; import org.opencv.imgcodecs.Imgcodecs; public class DisplayingImagesUsingSwings { public static ...
Read MoreHow to display OpenCV Mat object using JavaFX?
The JavaFX library provides a class with name ImageView using this you can display an image. This class accepts an object of the WritableImage class.To display an image Stored in OpenCV Mat object you need to convert it into a WritableImage object and pass it the ImageView class.Exampleimport java.awt.image.BufferedImage; import java.io.ByteArrayInputStream; import java.io.IOException; import java.io.InputStream; import javafx.application.Application; import javafx.embed.swing.SwingFXUtils; import javafx.scene.Group; import javafx.scene.Scene; import javafx.scene.image.ImageView; import javafx.scene.image.WritableImage; import javafx.stage.Stage; import javax.imageio.ImageIO; import org.opencv.core.Core; import org.opencv.core.Mat; import org.opencv.core.MatOfByte; import org.opencv.imgcodecs.Imgcodecs; public class DisplayingImagesJavaFX extends Application { @Override public void start(Stage stage) throws IOException { WritableImage writableImage = ...
Read MoreHow to convert a positive image to Negative to using OpenCV library?
Algorithm to convert an image to negativeGet the red green blue values of each pixelSubtract each color value from 255 and save them as new color values.Create a new pixel value from the modified colors.set the new value to the pixel.Implementation in JavaRead the required image using ImageIO.read() method.Get the height and width of the image.Using nested for loops traverse through each pixel in the image.Get the pixel value using the getRGB() method.Create a Color object bypassing the above-retrieved pixel value as parameter.Get the red, green, blue values from the color object using the getRed(), getGreen() and getBlue() methods respectively.Calculate ...
Read MoreExplain the Mat class in Java OpenCV library
In OpenCV, images are stored in Using Mat object. It is nothing but an n-dimensional array and is used to store image data of grayscale or color images, voxel volumes, vector fields, point clouds, tensors, histograms, etc.If you try to read an image using the OpenCV library it will be read to a Mat object.Mat matrix = Imgcodecs.imread(filePath);You can instantiate this class manually using one of the following constructors −Mat() − A no-arg constructor, used to create an empty matrix and pass this to other OpenCV methods.Mat(int rows, int cols, int type) − This constructor accepts three parameters of integer ...
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