如何使用
Floyd–Steinberg dithering将24位PNG转换为3位PNG？应该使用java.awt.image.BufferedImage来获取和设置RGB值.
在维基百科上,给出了如何将16位转换为8位图像的示例：
find_closest_palette_color(oldpixel) = (oldpixel + 128) / 256
基于此,有没有想到如何适应上面的例子来实现目标？
解决方法
使用
image.getRGB(x,y)和
image.setRGB(x,y,color),并从
wikipedia article使用
pseudocode.请注意,维基上的代码不会说如何“减”,“添加”和“乘”颜色. (下面的T3类处理“颜色”操作.)
下面的代码将会产生这个截图：
class Test {
private static BufferedImage floydSteinbergDithering(BufferedImage img) {
C3[] palette = new C3[] {
new C3( 0,0),new C3( 0,255),255,new C3(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,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(100,300);
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,this);
}
});
frame.add(new JComponent() {
@Override
protected void paintComponent(Graphics g) {
super.paintComponent(g);
g.drawImage(dietered,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));
}
}
}
