java - Drawing a graphical histogram

Question

I am working on a project and I would like to display a single line histogram that looks like a bar graph except each line in the bar graph represents a pixel and its greyscale value.

I have a array full of greyscale values, I just need to put them into this histogram and have it display the lines which will represent the values.. sort of like this

IMAGE             [minimize][maximize][close]



    picture                histogram

                          I
   (Loaded Picture)       I       I
                          I  I    I
                          I  I  I I  

[open][save]

And below is the code loading the array... I just need to get some code that will use those greyscale values and represent them as bars like above.

 public void showImage(File fileName) {
        Scanner scan;
        try {
            scan = new Scanner(fileName);
            typefile = scan.next();
            iname = scan.next();       
            width = scan.nextInt();
            height = scan.nextInt();
            maxshade = scan.nextInt();
            array = new int[width][height];


            for(int r = 0; r < array.length; r++){
                for(int c = 0; c < array[r].length; c++){
                    array[r][c] = scan.nextInt();                       




            imageArray = array;         
            repaint();                  


        } catch (FileNotFoundException e) {
            e.printStackTrace();
        }

 }

I know I have to do something like...

     int hist[] = new int[256];
     for (int r = 0; r < array.length; r++)
            for (int c = 0; c < array[r].length; c++)
                hist[array[r][c]]++;

But I don't know where to go from there or how to draw my graph.

Answer 1

Something like

Perhaps??

Personally, I'd still use something like JFreeChart, but this was a fun little exercise...

import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.geom.Rectangle2D;
import java.util.Map;
import java.util.TreeMap;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JScrollPane;

public class TestHisogram {
//http://stackoverflow.com/a/12520104/714968

    public static void main(String[] args) {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                new TestHisogram();
            }
        });
    }

    public TestHisogram() {
        // For this example, I just randomised some data, you would
        // Need to load it yourself...
        int width = 256;
        int height = 256;
        int[][] data = new int[width][height];
        for (int c = 0; c < height; c++) {
            for (int r = 0; r < width; r++) {
                data[c][r] = (int) (256 * Math.random());
            }
        }
        Map<Integer, Integer> mapHistory = new TreeMap<Integer, Integer>();
        for (int c = 0; c < data.length; c++) {
            for (int r = 0; r < data[c].length; r++) {
                int value = data[c][r];
                int amount = 0;
                if (mapHistory.containsKey(value)) {
                    amount = mapHistory.get(value);
                    amount++;
                } else {
                    amount = 1;
                }
                mapHistory.put(value, amount);
            }
        }
        JFrame frame = new JFrame("Test");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setLayout(new BorderLayout());
        frame.add(new JScrollPane(new Graph(mapHistory)));
        frame.pack();
        frame.setLocationRelativeTo(null);
        frame.setVisible(true);
    }

    protected class Graph extends JPanel {

        protected static final int MIN_BAR_WIDTH = 4;
        private Map<Integer, Integer> mapHistory;

        public Graph(Map<Integer, Integer> mapHistory) {
            this.mapHistory = mapHistory;
            int width = (mapHistory.size() * MIN_BAR_WIDTH) + 11;
            Dimension minSize = new Dimension(width, 128);
            Dimension prefSize = new Dimension(width, 256);
            setMinimumSize(minSize);
            setPreferredSize(prefSize);
        }

        @Override
        protected void paintComponent(Graphics g) {
            super.paintComponent(g);
            if (mapHistory != null) {
                int xOffset = 5;
                int yOffset = 5;
                int width = getWidth() - 1 - (xOffset * 2);
                int height = getHeight() - 1 - (yOffset * 2);
                Graphics2D g2d = (Graphics2D) g.create();
                g2d.setColor(Color.DARK_GRAY);
                g2d.drawRect(xOffset, yOffset, width, height);
                int barWidth = Math.max(MIN_BAR_WIDTH,
                        (int) Math.floor((float) width
                        / (float) mapHistory.size()));
                System.out.println("width = " + width + "; size = "
                        + mapHistory.size() + "; barWidth = " + barWidth);
                int maxValue = 0;
                for (Integer key : mapHistory.keySet()) {
                    int value = mapHistory.get(key);
                    maxValue = Math.max(maxValue, value);
                }
                int xPos = xOffset;
                for (Integer key : mapHistory.keySet()) {
                    int value = mapHistory.get(key);
                    int barHeight = Math.round(((float) value
                            / (float) maxValue) * height);
                    g2d.setColor(new Color(key, key, key));
                    int yPos = height + yOffset - barHeight;
//Rectangle bar = new Rectangle(xPos, yPos, barWidth, barHeight);
                    Rectangle2D bar = new Rectangle2D.Float(
                            xPos, yPos, barWidth, barHeight);
                    g2d.fill(bar);
                    g2d.setColor(Color.DARK_GRAY);
                    g2d.draw(bar);
                    xPos += barWidth;
                }
                g2d.dispose();
            }
        }
    }
}