- OpenCV - GUI
- OpenCV - Writing an Image
- OpenCV - Reading Images
- OpenCV - Storing Images
- OpenCV - Environment
- OpenCV - Overview
- OpenCV - Home
Types of Images
Image Conversion
Drawing Functions
- OpenCV - Adding Text
- OpenCV - Drawing Arrowed Lines
- OpenCV - Drawing Convex Polylines
- OpenCV - Drawing Polylines
- OpenCV - Drawing an Ellipse
- OpenCV - Drawing a Rectangle
- OpenCV - Drawing a Line
- OpenCV - Drawing a Circle
Blur
Filtering
- OpenCV - Image Pyramids
- OpenCV - Morphological Operations
- OpenCV - Erosion
- OpenCV - Dilation
- OpenCV - Filter2D
- OpenCV - SQRBox Filter
- OpenCV - Box Filter
- OpenCV - Bilateral Filter
Thresholding
Sobel Derivatives
Transformation Operations
Camera and Face Detection
Geometric Transformations
Miscellaneous Chapters
OpenCV Useful Resources
Selected Reading
- Who is Who
- Computer Glossary
- HR Interview Questions
- Effective Resume Writing
- Questions and Answers
- UPSC IAS Exams Notes
OpenCV - Colored Images to GrayScale
In the earper chapters, we discussed how to read an input image as different types (binary, grayscale, BGR, etc.). In this chapter, we will learn how to convert one type of image to another.
The class named Imgproc of the package org.opencv.imgproc provides methods to convert an image from one color to another.
Converting Colored Images to Grayscale
A method named cvtColor() is used to convert colored images to grayscale. Following is the syntax of this method.
cvtColor(Mat src, Mat dst, int code)
This method accepts the following parameters −
src − A matrix representing the source.
dst − A matrix representing the destination.
code − An integer code representing the type of the conversion, for example, RGB to Grayscale.
You can convert colored images to gray scale by passing the code Imgproc.COLOR_RGB2GRAY along with the source and destination matrices as a parameter to the cvtColor() method.
Example
The following program demonstrates how to read a colored image as a grayscale image and display it using JavaFX window.
import java.awt.image.BufferedImage; import org.opencv.core.Core; import org.opencv.core.Mat; import org.opencv.imgcodecs.Imgcodecs; import org.opencv.imgproc.Imgproc; import javafx.apppcation.Apppcation; 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; pubpc class ColorToGrayscale extends Apppcation { @Override pubpc void start(Stage stage) throws Exception { WritableImage writableImage = loadAndConvert(); // Setting the image view ImageView imageView = new ImageView(writableImage); // Setting the position of the image imageView.setX(10); imageView.setY(10); // setting the fit height and width of the image view imageView.setFitHeight(400); imageView.setFitWidth(600); // Setting the preserve ratio of the image view imageView.setPreserveRatio(true); // Creating a Group object Group root = new Group(imageView); // Creating a scene object Scene scene = new Scene(root, 600, 400); // Setting title to the Stage stage.setTitle("Colored to grayscale image"); // Adding scene to the stage stage.setScene(scene); // Displaying the contents of the stage stage.show(); } pubpc WritableImage loadAndConvert() throws Exception { //Loading the OpenCV core pbrary System.loadLibrary( Core.NATIVE_LIBRARY_NAME ); String input = "C:/EXAMPLES/OpenCV/sample.jpg"; //Reading the image Mat src = Imgcodecs.imread(input); //Creating the empty destination matrix Mat dst = new Mat(); //Converting the image to gray sacle and saving it in the dst matrix Imgproc.cvtColor(src, dst, Imgproc.COLOR_RGB2GRAY); //Extracting data from the transformed image (dst) byte[] data1 = new byte[dst.rows() * dst.cols() * (int)(dst.elemSize())]; dst.get(0, 0, data1); //Creating Buffered image using the data BufferedImage bufImage = new BufferedImage(dst.cols(),dst.rows(), BufferedImage.TYPE_BYTE_GRAY); //Setting the data elements to the image bufImage.getRaster().setDataElements(0, 0, dst.cols(), dst.rows(), data1); //Creating a WritableImage WritableImage writableImage = SwingFXUtils.toFXImage(bufImage, null); System.out.println("Converted to Grayscale"); return writableImage; } pubpc static void main(String args[]) throws Exception { launch(args); } }
Input Image
Assume that following is the input image sample.jpg specified in the above program.
![Sample Image](/opencv/images/sample_image.jpg)
Output Image
On executing the program, you will get the following output.
![Colored Images to GrayScale Output](/opencv/images/colored_images_to_grayscale_output.jpg)