CODEWITHSUNDEEP
javaimage-processingdithering
Scholle
Scholle

Reputation: 1521

How to convert a 24 Bit PNG to 3 Bit PNG using Floyd–Steinberg dithering?

How to convert a 24 Bit PNG to 3 Bit PNG using Floyd–Steinberg dithering? java.awt.image.BufferedImage should be used to get and set RGB values.

On wikipedia, an example is given on how to convert a 16 Bit to a 8 Bit image:

find_closest_palette_color(oldpixel) = (oldpixel + 128) / 256

Based on this, are there any ideas on how to fit the example above in order to achieve the goal?

Upvotes: 12

Views: 10705

Answers (5)

runholen
runholen

Reputation: 970

Although this is an old post, it might be increasingly relevant at the time of writing, with the advent of e-ink labels in shops, where colors available are usually only BWR (black, white and red, 3 colors) or maybe in some instances BWRY (4 colors) In automating making images in this regard, I implemented the accepted answer at https://gist.github.com/naikrovek/643a9799171d20820cb9 as my floydSteinbergDithering-algorithm. Although this seems to work fine on eg 8-bit palettes, there seem to be a bug in the algorithm that makes poor results when using palettes with only 3 or 4 colors. This can be spotted easily in the beak of scrooge here (see image) enter image description here

If testing the same image on eg ditherit.com, the beak is fine. However, I found that this bug does not occur in the java implementation at https://github.com/Regarrzo/Java-Floyd-Steinberg-Dithering/ (se example image for results) enter image description here

I hope this can improve image quality for other people working with BWR palette on those small e-ink-labels ;-)

Upvotes: 1

dacwe
dacwe

Reputation: 43504

Use image.getRGB(x, y) and image.setRGB(x, y, color) and use the pseudocode from the wikipedia article. Note that code on the wiki does not say how to "subtract", "add" and "multiply" colors. (The T3 class below handles "color" manipulation.)

The code below will produce this screenshot:

screenshot

class Test {
  private static BufferedImage floydSteinbergDithering(BufferedImage img) {

    C3[] palette = new C3[] {
        new C3(  0,   0,   0),
        new C3(  0,   0, 255),
        new C3(  0, 255,   0),
        new C3(  0, 255, 255),
        new C3(255,   0,   0),
        new C3(255,   0, 255),
        new C3(255, 255,   0),
        new C3(255, 255, 255)
    };

    int w = img.getWidth();
    int h = img.getHeight();

    C3[][] d = new C3[h][w];

    for (int y = 0; y < h; y++) 
      for (int x = 0; x < w; x++) 
        d[y][x] = new C3(img.getRGB(x, y));

    for (int y = 0; y < img.getHeight(); y++) {
      for (int x = 0; x < img.getWidth(); x++) {

        C3 oldColor = d[y][x];
        C3 newColor = findClosestPaletteColor(oldColor, palette);
        img.setRGB(x, y, newColor.toColor().getRGB());

        C3 err = oldColor.sub(newColor);

        if (x+1 < w)         d[y  ][x+1] = d[y  ][x+1].add(err.mul(7./16));
        if (x-1>=0 && y+1<h) d[y+1][x-1] = d[y+1][x-1].add(err.mul(3./16));
        if (y+1 < h)         d[y+1][x  ] = d[y+1][x  ].add(err.mul(5./16));
        if (x+1<w && y+1<h)  d[y+1][x+1] = d[y+1][x+1].add(err.mul(1./16));
      }
    }

    return img;
  }

  private static C3 findClosestPaletteColor(C3 c, C3[] palette) {
    C3 closest = palette[0];

    for (C3 n : palette) 
      if (n.diff(c) < closest.diff(c))
        closest = n;

    return closest;
  }

  public static void main(String[] args) throws IOException {

    final BufferedImage normal  = ImageIO.read(new URL("http://upload.wikimedia.org/wikipedia/en/2/24/Lenna.png")).getSubimage(100, 100, 300, 300);
    final BufferedImage dietered = floydSteinbergDithering(ImageIO.read(new URL("http://upload.wikimedia.org/wikipedia/en/2/24/Lenna.png"))).getSubimage(100, 100, 300, 300);

    JFrame frame = new JFrame("Test");
    frame.setLayout(new GridLayout(1, 2));

    frame.add(new JComponent() {
      @Override
      protected void paintComponent(Graphics g) {
         super.paintComponent(g);
         g.drawImage(normal, 0, 0, this);
      }
    });
    frame.add(new JComponent() {
      @Override
      protected void paintComponent(Graphics g) {
         super.paintComponent(g);
         g.drawImage(dietered, 0, 0, this);
      }
    });

    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.setSize(400, 400);
    frame.setVisible(true);
  }


  static class C3 {
    int r, g, b;

    public C3(int c) {
      Color color = new Color(c);
      this.r = color.getRed();
      this.g = color.getGreen();
      this.b = color.getBlue();
    }
    public C3(int r, int g, int b) {
      this.r = r;
      this.g = g;
      this.b = b;
    }

    public C3 add(C3 o) {
      return new C3(r + o.r, g + o.g, b + o.b);
    }
    public C3 sub(C3 o) {
      return new C3(r - o.r, g - o.g, b - o.b);
    }
    public C3 mul(double d) {
      return new C3((int) (d * r), (int) (d * g), (int) (d * b));
    }
    public int diff(C3 o) {
      return Math.abs(r - o.r) +  Math.abs(g - o.g) +  Math.abs(b - o.b);
    }

    public int toRGB() {
      return toColor().getRGB();
    }
    public Color toColor() {
      return new Color(clamp(r), clamp(g), clamp(b));
    }
    public int clamp(int c) {
      return Math.max(0, Math.min(255, c));
    }
  }
}

Upvotes: 36

Ivan Kuckir
Ivan Kuckir

Reputation: 2549

By the way, here is the code and live demo of Floyd-Steinberg in video! :)

http://blog.ivank.net/floyd-steinberg-dithering-in-javascript.html

Upvotes: 0

Mark Amabile
Mark Amabile

Reputation: 152

source code needs the missing method "diff" in the static class C3. otherwise, it doesn't compile or work.

here's the missing diff method:

public int diff(C3 o) {
    int Rdiff = o.r - this.r;
    int Gdiff = o.g - this.g;
    int Bdiff = o.b - this.b;
    int distanceSquared = Rdiff*Rdiff + Gdiff*Gdiff + Bdiff*Bdiff;
    return distanceSquared;
}

Upvotes: 2

Dmitry Negoda
Dmitry Negoda

Reputation: 3189

You can use JAI: http://java.sun.com/products/java-media/jai/forDevelopers/jai1_0_1guide-unc/Image-manipulation.doc.html

Upvotes: 0

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