Question

如何使用Floyd–Steinberg dithering将24位PNG转换为3位PNG？应使用java.awt.image.BufferedImage来获取和设置RGB值。

在维基百科上，给出了一个如何将16位转换为8位图像的示例：

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

基于此，有没有关于如何适应上述示例以实现目标的想法？

Answer 1

使用image.getRGB(x, y)和image.setRGB(x, y, color)并使用pseudocode中的wikipedia article。请注意，wiki上的代码没有说明如何“减去”，“添加”和“乘以”颜色。（下面的T3类处理“颜色”操作。）

以下代码将生成此屏幕截图：

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));
    }
  }
}

Answer 2

源代码需要静态类C3中缺少的方法“diff”。否则，它不会编译或工作。

这是缺少的diff方法：

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;
}

Answer 3

您可以使用JAI：http://java.sun.com/products/java-media/jai/forDevelopers/jai1_0_1guide-unc/Image-manipulation.doc.html

Answer 4

顺便说一句，这是Floyd-Steinberg在视频中的代码和现场演示！：）

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

如何使用Floyd-Steinberg抖动将24位PNG转换为3位PNG？

4 个答案: