Demonstrates different methods of scaling images in JavaFX and the effects of scaling with each.

ImageScaler.java

import javafx.application.*;
import javafx.geometry.HPos;
import javafx.geometry.Pos;
import javafx.scene.*;
import javafx.scene.control.*;
import javafx.scene.image.*;
import javafx.scene.layout.*;
import javafx.stage.Stage;
 
public class ImageScaler extends Application {
  private static final String IMAGE_LOC = 
    "http://icons.iconarchive.com/icons/martin-berube/character/32/Robot-icon.png";
  
  private static final int SCALE_FACTOR = 6;
  
  private Image image;
  private int   scaledImageSize;
  
  @Override public void init() {
    image = new Image(
      IMAGE_LOC
    );
    
    scaledImageSize = (int) image.getWidth() * SCALE_FACTOR;
  }
  
  @Override public void start(Stage stage) {
    GridPane layout = new GridPane();
    layout.setHgap(10);
    layout.setVgap(10);
    
    ImageView originalImageView = new ImageView(image);
    StackPane originalImageViewStack = new StackPane();
    originalImageViewStack.getChildren().add(originalImageView);
    originalImageViewStack.setMinWidth(scaledImageSize);
    
    ImageView fittedImageView = new ImageView(image);
    fittedImageView.setSmooth(false);
    fittedImageView.setFitWidth(scaledImageSize);
    fittedImageView.setFitHeight(scaledImageSize);
    
    ImageView scaledImageView = new ImageView(image);
    scaledImageView.setSmooth(false);
    scaledImageView.setScaleX(SCALE_FACTOR);
    scaledImageView.setScaleY(SCALE_FACTOR);
    Group scaledImageViewGroup = new Group(scaledImageView);
    
    ImageView sizedImageInView = new ImageView(
      new Image(
        IMAGE_LOC, 
        scaledImageSize, 
        scaledImageSize, 
        false, 
        false
      )
    );

    ImageView resampledImageView = new ImageView(
      resample(
        image, 
        SCALE_FACTOR
      )
    );
    
    layout.addRow(
      0, 
        withTooltip(
          originalImageViewStack,
          "Unmodified image"
        ),
        withTooltip(
          sizedImageInView,
          "Image sized in Image constructor - Image smoothing false"
        ),
        withTooltip(
          fittedImageView,
          "Image fitted using ImageView fitWidth/fitHeight - ImageView smoothing false"
        ),
        withTooltip(
          scaledImageViewGroup,
          "ImageView scaled with Node scaleX/scaleY - ImageView smoothing false"
        ),
        withTooltip(
          resampledImageView,
          "Image manually recreated as a new WritableImage using a PixelWriter"
        )
    );
    
    layout.addRow(
      1, 
        centeredLabel("Original"),
        centeredLabel("Sized"),
        centeredLabel("Fitted"),
        centeredLabel("Scaled"),
        centeredLabel("Resampled")
    );
    layout.setAlignment(Pos.CENTER);
    
    layout.setStyle("-fx-background-color: cornsilk; -fx-padding: 10;");
    stage.setScene(
      new Scene(layout)
    );
    stage.show();
  }
  
  private Node withTooltip(Node node, String text) {
    Tooltip.install(node, new Tooltip(text));
    return node;
  }
  
  private Label centeredLabel(String text) {
    Label label = new Label(text);
    GridPane.setHalignment(label, HPos.CENTER);

    return label;
  }
  
  private Image resample(Image input, int scaleFactor) {
    final int W = (int) input.getWidth();
    final int H = (int) input.getHeight();
    final int S = scaleFactor;
    
    WritableImage output = new WritableImage(
      W * S,
      H * S
    );
    
    PixelReader reader = input.getPixelReader();
    PixelWriter writer = output.getPixelWriter();
    
    for (int y = 0; y < H; y++) {
      for (int x = 0; x < W; x++) {
        final int argb = reader.getArgb(x, y);
        for (int dy = 0; dy < S; dy++) {
          for (int dx = 0; dx < S; dx++) {
            writer.setArgb(x * S + dx, y * S + dy, argb);
          }
        }
      }
    }
    
    return output;
  }
  
  public static void main(String[] args) { Application.launch(args); }
}

Still works 10 years later with OpenFX 17

https://openjfx.io/javadoc/17/javafx.graphics/javafx/scene/image/package-summary.html