在Java中将灰度转换为颜色渐变？

Question

是否有任何通用算法或提供的类用于将灰度值（0-255）映射到颜色渐变中的值？我在想这样的事情：

   public Color mapGrayscaleValue (byte value, Color[] gradientColors);

我希望这能为我提供的灰度云层覆盖雷达图像提供更清晰的亮点

Answer 1

经过思考，我只是创建了一个255x1 BuffereImage，然后使用GradientPaint类为自己创建了一个颜色查找表。使用这种方法，我甚至可以加载手动创建的颜色表。对于其他人：

// Set up the reference image that will be used as the color map

int width = 255;
int height = 1;

BufferedImage colorGradientImage = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB);

Graphics2D g2 = (Graphics2D) colorGradientImage.getGraphics();

Paint p = new LinearGradientPaint(
            0, 0, width, 0, new float[] { 0.0f, 0.7f, 0.8f },
            new Color[] { Color.YELLOW, Color.BLUE, Color.RED }
            );

g2.setPaint(p);
g2.fillRect(0, 0, width, height);

g2.dispose();

// Now process the data, using the colour map we created above for the colour values

// pixel data is matrix of values, from 0-255
int[][] pixelData = getSourceValues();

BufferedImage myImage = new BufferedImage(pixelData[0].length, pixelData.length, BufferedImage.TYPE_INT_RGB);
for (int y=0; y<pixelData.length; y++) {
   for (int x=0; x<myImage[y].length; x++) {
       myImage.setRGB(x,y, colorGradientImage.getRGB(pixelData,0));
   }
}

我可能已经将colorGradientImage转换为255长度的数组，但现在这就可以了

如果有人知道另一种或更好的方法，我总是很感兴趣

Answer 2

如果您正在使用java.awt.image，那么应该查看^{}。它（我认为）正是你想要的

您需要以某种方式为渐变生成256个RGB值，并围绕它们创建一个模型，然后可以使用新模型从灰度光栅创建BufferedImage

下面是一个简单明了的例子：

import javax.swing.*;
import java.awt.*;
import java.awt.image.*;
import javax.imageio.*;
import java.net.*;

class ColorModelEx implements Runnable {
    public static void main(String[] args) {
        SwingUtilities.invokeLater(new ColorModelEx());
    }

    @Override
    public void run() {
        JFrame frame = new JFrame();
        JLabel label;
        try {
            label = new JLabel(new ImageIcon(createImage(
                Color.yellow, Color.red, Color.blue)));
        } catch (Exception e) {
            throw new AssertionError(e);
        }

        frame.add(label);
        frame.pack();
        frame.setResizable(false);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setVisible(true);
    }

    static BufferedImage createImage(Color... colors) throws Exception {
        if ((256 % (colors.length - 1)) != 0)
            throw new IllegalArgumentException();

        BufferedImage original =
            ImageIO.read(new URL("http://i.stack.imgur.com/7bI1Y.jpg"));

        final int w = original.getWidth();
        final int h = original.getHeight();

        BufferedImage gray =
            new BufferedImage(w, h, BufferedImage.TYPE_BYTE_GRAY);
        Graphics2D g2 = gray.createGraphics();
        g2.drawImage(original, 0, 0, null);

        byte[] r = new byte[256];
        byte[] g = new byte[256];
        byte[] b = new byte[256];

        final int fade = (256 / (colors.length - 1));

        // (generate all 256 RGB values by
        // fading between the colors supplied)
        for (int i = 0; i < 256; ++i) {
            Color c0 = colors[(i / fade)];
            Color c1 = colors[(i / fade) + 1];

            float amt = (i % fade) / ((float) fade);

            r[i] = getChannel(amt, c0.getRed(),   c1.getRed());
            g[i] = getChannel(amt, c0.getGreen(), c1.getGreen());
            b[i] = getChannel(amt, c0.getBlue(),  c1.getBlue());
        }

        // (remap same pixels to new model)
        return new BufferedImage(
            new IndexColorModel(8, 256, r, g, b),
            gray.getRaster(), false, null);
    }

    static byte getChannel(float amt, int ch0, int ch1) {
        return (byte)
            ((ch0 * (1 - amt)) + (ch1 * amt));
    }
}

_{（来自here的图像。）}

其他一些有用的地方：

• Efficiently color cycling an image in Java
• Changing the ColorModel of a BufferedImage