Introduction
The problem discussed in this post is quite common. In fact, you can find lots and lots of tutorials on it. You can take this post as one more addition to the available resources. The problem that we are going to discuss in this post is "Converting Colored Image To Black and White or to Grayscale".
In computer science terminology, color image is known as the RGB image. RGB stands for RED, GREEN, BLUE. Since these are the primary colors and all the other colors are made up of these colors, all the colored images that we click with our digital cameras fall into the category of RGB images.
Similarly, the images that are black and white, in computer terminology are known as Grayscale images. Grayscale means having different shades of gray. Basically, the black and white images do not have black and white colors, they have different shades of gray color. Below, I have explained algorithms for converting color images to black and white.
Algorithm for Grayscale Conversion
There are various algorithms to convert the color image to black and white. Here I am going to discuss two of them. One is naive and not very efficient whereas the second one is much more efficient. But before we begin the algorithm we must understand how does the algorithm work? All grayscale conversion includes these basic steps,
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Get the red, green and blue value of pixels.
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Use fancy maths to turn those numbers into a single gray value.
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Replace the original red, green and blue values into a grayscale value.
Method 1 - Averaging (aka “quick and dirty”)
This method is the most boring. Averaging is the most common grayscale method and it works like this
GRAY = (RED + GREEN + BLUE) / 3
Basically in this algorithm, we calculate the value of gray color as shown above and assign it to red, green and blue values of the pixels. Fast, simple – no wonder this is a go-to method for the rookie programmers. This formula generates a reasonably nice grayscale equivalent, and its simplicity makes it easy to implement and optimize. However, this formula has its own shortcomings. While fast and simple this formula does a poor job of representing shades of gray relative to the way humans perceive luminosity (brightness). For that, we need a bit more complex.
Method 2 - Luminescence Method (Correction for human eye)
The first method fails because of the fact that cone density is not uniform across colors. Humans perceive green more strongly than red, and red more strongly than blue. This is because much of the natural world appear green, so humans have evolved greater sensitivity to green light. Because humans do not perceive all colors equally, the “average method” of grayscale is inaccurate.
In this method instead of treating red, blue and green light equally, a good grayscale conversion will weight each color based on how the human eye perceives it. A common formula found in image processor programs is shown below,
Gray = (Red * 0.3 + Green * 0.59 + Blue * 0.11)
This method is used in the code to make the color image black and white, or RGB image to Grayscale. The algorithm works in three basic steps as explained above.
Below you can see the source code,
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- package grayscaleconversion;
- import java.io.File;
- import java.net.MalformedURLException;
- import java.util.logging.Level;
- import java.util.logging.Logger;
- import javafx.application.Application;
- import javafx.concurrent.Service;
- import javafx.concurrent.Task;
- import javafx.concurrent.WorkerStateEvent;
- import javafx.event.ActionEvent;
- import javafx.scene.Group;
- import javafx.scene.Scene;
- import javafx.scene.control.Button;
- import javafx.scene.control.ProgressBar;
- import javafx.scene.image.Image;
- import javafx.scene.image.ImageView;
- import javafx.scene.image.PixelReader;
- import javafx.scene.image.PixelWriter;
- import javafx.scene.image.WritableImage;
- import javafx.scene.paint.Color;
- import javafx.scene.text.Font;
- import javafx.stage.FileChooser;
- import javafx.stage.Stage;
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- public class GrayScaleConversion extends Application {
- private Image image;
- private ImageView iv = new ImageView();
- private Button selectBTN = new Button();
- private Button convertBTN = new Button();
- private PixelReader preader;
- private PixelWriter pwriter;
- private File filePath = null;
- private ProgressBar pbar = new ProgressBar(0);
- WritableImage wimage;
- @Override
- public void start(Stage primaryStage) {
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- Font poorRichard = new Font("Poor Richard", 16);
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- selectBTN.setText("Select Image");
- selectBTN.setFont(poorRichard);
- selectBTN.setLayoutX(20);
- selectBTN.setLayoutY(450);
- convertBTN.setText("Convert GrayScale");
- convertBTN.setFont(poorRichard);
- convertBTN.setLayoutX(200);
- convertBTN.setLayoutY(450);
- iv.setFitHeight(300);
- iv.setFitWidth(300);
- iv.setLayoutX(100);
- iv.setLayoutY(0);
- pbar.setLayoutX(20);
- pbar.setLayoutY(320);
- pbar.setPrefWidth(460);
- pbar.setVisible(false);
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- selectBTN.setOnAction((ActionEvent ae) -> {
- FileChooser fc = new FileChooser();
- filePath = fc.showOpenDialog(primaryStage);
- if (filePath != null) {
- System.out.println();
- try {
- image = new Image(filePath.toURI().toURL().toExternalForm());
- iv.setImage(image);
- } catch (MalformedURLException ex) {
- Logger.getLogger(GrayScaleConversion.class.getName()).log(Level.SEVERE, null, ex);
- }
- }
- });
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- convertBTN.setOnAction((ActionEvent ae) -> {
- pbar.progressProperty().unbind();
- pbar.progressProperty().bind(RGBToGRAYSCALE.progressProperty());
- pbar.setVisible(true);
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- RGBToGRAYSCALE.restart();
- });
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- RGBToGRAYSCALE.setOnSucceeded((WorkerStateEvent we) -> {
- iv.setImage(wimage);
- pbar.setVisible(false);
- });
- Group root = new Group();
- Scene scene = new Scene(root, 500, 500);
- root.getChildren().add(selectBTN);
- root.getChildren().add(convertBTN);
- root.getChildren().add(iv);
- root.getChildren().add(pbar);
- primaryStage.setTitle("Grayscale Conversion");
- primaryStage.setScene(scene);
- primaryStage.setResizable(false);
- primaryStage.show();
- }
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- Service < Void > RGBToGRAYSCALE = new Service < Void > () {
- @Override
- protected Task < Void > createTask() {
- return new Task < Void > () {
- @Override
- protected Void call() throws Exception {
- image = new Image(filePath.toURI().toURL().toExternalForm());
- preader = image.getPixelReader();
- wimage = new WritableImage((int) image.getWidth(), (int) image.getHeight());
- pwriter = wimage.getPixelWriter();
- int count = 0;
- for (int i = 0; i < (int) image.getHeight(); i++) {
- for (int j = 0; j < (int) image.getWidth(); j++) {
- count += 1;
- Color col = preader.getColor(j, i);
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- pwriter.setColor(j, i, new Color((col.getRed() * 0.3 + col.getGreen() * 0.59 + col.getBlue() * 0.11), (col.getRed() * 0.3 + col.getGreen() * 0.59 + col.getBlue() * 0.11), (col.getRed() * 0.3 + col.getGreen() * 0.59 + col.getBlue() * 0.11), 1.0));
- updateProgress(count, image.getHeight() * image.getWidth());
- }
- }
- return null;
- }
- };
- }
- };
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- public static void main(String[] args) {
- launch(args);
- }
- }