如何使用Floyd-Steinberg抖动将24位PNG转换为3位PNG？ [英] How to convert a 24 Bit PNG to 3 Bit PNG using Floyd–Steinberg dithering?

问题描述

如何使用 Floyd-Steinberg抖动将24位PNG转换为3位PNG？ java.awt.image.BufferedImage 应该用于获取和设置RGB值。

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.

在维基百科上，给出了如何将16位转换为8位图像的示例：

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

基于此，是否有任何关于如何适应上述示例以实现目标的想法？

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

推荐答案

使用 image.getRGB（x，y） 和 image.setRGB（x，y，color） 并使用伪代码 http://en.wikipedia.org/wiki/Floyd%E2%80%93Steinberg_ditheringrel =noreferrer>维基百科文章。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。）

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.)

下面的代码将生成此屏幕截图：

The code below will produce this 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));
    }
  }
}

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