I tried to construct a byte array and set it to a WritableImage using PixelWriter's setPixels method.

If I use a byte-indexed pixel format, I get an NPE.


java.lang.NullPointerException
at com.sun.javafx.image.impl.BaseByteToByteConverter.<init>(BaseByteToByteConverter.java:45)
at com.sun.javafx.image.impl.General$ByteToByteGeneralConverter.<init>(General.java:69)
at com.sun.javafx.image.impl.General.create(General.java:44)
at com.sun.javafx.image.PixelUtils.getB2BConverter(PixelUtils.java:223)
at com.sun.prism.Image$ByteAccess.setPixels(Image.java:770)
at com.sun.prism.Image.setPixels(Image.java:606)
at javafx.scene.image.WritableImage$2.setPixels(WritableImage.java:199)

Short self-contained correct example to reproduce:

import java.nio.ByteBuffer;
 
import javafx.application.Application;
import javafx.scene.Scene;
import javafx.scene.image.ImageView;
import javafx.scene.image.PixelFormat;
import javafx.scene.image.WritableImage;
import javafx.scene.layout.BorderPane;
import javafx.stage.Stage;
 
public class IndexedColorTestApp extends Application {
 
    public static void main(String[] args) {
        launch(args);
    }
 
    @Override
    public void start(Stage primaryStage) {
        BorderPane borderPane = new BorderPane();
        Scene scene = new Scene(borderPane, 600, 1100);
        primaryStage.setScene(scene);
 
        ImageView imageView = new ImageView();
        borderPane.setCenter(imageView);
        primaryStage.show();
 
        int imageWidth = 200;
        int imageHeight = 200;
        WritableImage writableImage = new WritableImage(imageWidth, imageHeight);
 
        // this works
        byte[] rgbBytePixels = new byte[imageWidth * imageHeight * 3];
        PixelFormat<ByteBuffer> byteRgbFormat = PixelFormat.getByteRgbInstance();
        writableImage.getPixelWriter().setPixels(0, 0, imageWidth, imageHeight,
                                                 byteRgbFormat, rgbBytePixels, 0, imageWidth * 3);
        imageView.setImage(writableImage);
 
        // this throws an NPE in setPixels()
        byte[] indexedBytePixels = new byte[imageWidth * imageHeight];
        int[] colorPalette = new int[256];
        PixelFormat<ByteBuffer> byteIndexedFormat = PixelFormat.createByteIndexedInstance(colorPalette);
        writableImage.getPixelWriter().setPixels(0, 0, imageWidth, imageHeight,
                                                 byteIndexedFormat, indexedBytePixels, 0, imageWidth);
        imageView.setImage(writableImage);
    }
 
}