如何使用Java将图像转换为黑白

Question

我在 imagemagick 中使用如下命令将图像转换为黑白：

convert myimg.png -monochrome  out3.png

我想知道它是否有可能在 Java 中实现相同的结果？不使用 Im4Java 或 JMagick？

Answer 1

我想这取决于您所说的“单色”/“黑白”......

public class TestBlackAndWhite {

    public static void main(String[] args) {
        new TestBlackAndWhite();
    }

    public TestBlackAndWhite() {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                try {
                    UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
                } catch (Exception ex) {
                }

                JFrame frame = new JFrame("Test");
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.add(new TestPane());
                frame.pack();
                frame.setLocationRelativeTo(null);
                frame.setVisible(true);

            }
        });
    }

    public class TestPane extends JPanel {

        private BufferedImage master;
        private BufferedImage grayScale;
        private BufferedImage blackWhite;

        public TestPane() {
            try {
                master = ImageIO.read(new File("C:/Users/shane/Dropbox/pictures/439px-Join!_It's_your_duty!.jpg"));
                grayScale = ImageIO.read(new File("C:/Users/shane/Dropbox/pictures/439px-Join!_It's_your_duty!.jpg"));
                ColorConvertOp op = new ColorConvertOp(ColorSpace.getInstance(ColorSpace.CS_GRAY), null);
                op.filter(grayScale, grayScale);

                blackWhite = new BufferedImage(master.getWidth(), master.getHeight(), BufferedImage.TYPE_BYTE_BINARY);
                Graphics2D g2d = blackWhite.createGraphics();
                g2d.drawImage(master, 0, 0, this);
                g2d.dispose();

            } catch (IOException ex) {
                ex.printStackTrace();
            }
        }

        @Override
        public Dimension getPreferredSize() {
            Dimension size = super.getPreferredSize();
            if (master != null) {
                size = new Dimension(master.getWidth() * 3, master.getHeight());
            }
            return size;
        }

        @Override
        protected void paintComponent(Graphics g) {
            super.paintComponent(g);
            if (master != null) {

                int x = (getWidth() - (master.getWidth() * 3)) / 2;
                int y = (getHeight() - master.getHeight()) / 2;

                g.drawImage(master, x, y, this);
                x += master.getWidth();
                g.drawImage(grayScale, x, y, this);
                x += master.getWidth();
                g.drawImage(blackWhite, x, y, this);

            }
        }


    }
}

Answer 2

试试这个粗略的例子。我们首先使用RescaleOp 使图像变亮或变暗。

import java.awt.*;
import java.awt.image.BufferedImage;
import java.awt.image.RescaleOp;
import java.net.URL;
import javax.imageio.ImageIO;
import javax.swing.*;
import javax.swing.event.ChangeEvent;
import javax.swing.event.ChangeListener;

class ColorToBlackAndWhite {

    /**
     * Returns the supplied src image brightened by a float value from 0 to 10.
     * Float values below 1.0f actually darken the source image.
     */
    public static BufferedImage brighten(BufferedImage src, float level) {
        BufferedImage dst = new BufferedImage(
                src.getWidth(), src.getHeight(), BufferedImage.TYPE_INT_RGB);
        float[] scales = {level, level, level};
        float[] offsets = new float[4];
        RescaleOp rop = new RescaleOp(scales, offsets, null);

        Graphics2D g = dst.createGraphics();
        g.drawImage(src, rop, 0, 0);
        g.dispose();

        return dst;
    }

    public static void main(String[] args) throws Exception {
        URL colorURL = new URL("http://i.stack.imgur.com/AuY9o.png");
        final BufferedImage colorImage = ImageIO.read(colorURL);

        float[] scales = {2f, 2f, 2f};
        float[] offsets = new float[4];
        RescaleOp rop = new RescaleOp(scales, offsets, null);

        final BufferedImage scaledImage = new BufferedImage(
                colorImage.getWidth(),
                colorImage.getHeight(),
                BufferedImage.TYPE_INT_RGB);
        Graphics2D g = scaledImage.createGraphics();
        g.drawImage(colorImage, rop, 0, 0);

        final BufferedImage grayImage = new BufferedImage(
                colorImage.getWidth(),
                colorImage.getHeight(),
                BufferedImage.TYPE_BYTE_GRAY);
        g = grayImage.createGraphics();
        g.drawImage(colorImage, 0, 0, null);

        final BufferedImage blackAndWhiteImage = new BufferedImage(
                colorImage.getWidth(),
                colorImage.getHeight(),
                BufferedImage.TYPE_BYTE_BINARY);
        g = blackAndWhiteImage.createGraphics();
        g.drawImage(colorImage, 0, 0, null);

        g.dispose();

        Runnable r = new Runnable() {

            @Override
            public void run() {
                JPanel gui = new JPanel(new BorderLayout(2, 2));
                JPanel images = new JPanel(new GridLayout(0, 2, 2, 2));
                gui.add(images, BorderLayout.CENTER);

                final JLabel scaled = new JLabel(new ImageIcon(scaledImage));
                final JSlider brighten = new JSlider(0, 1000, 100);
                gui.add(brighten, BorderLayout.PAGE_START);
                ChangeListener cl = new ChangeListener() {

                    @Override
                    public void stateChanged(ChangeEvent e) {
                        int val = brighten.getValue();
                        float valFloat = val / 1000f;
                        BufferedImage bi = brighten(colorImage, valFloat);
                        BufferedImage bw = new BufferedImage(
                                colorImage.getWidth(),
                                colorImage.getHeight(),
                                BufferedImage.TYPE_BYTE_BINARY);
                        Graphics g = bw.createGraphics();
                        g.drawImage(bi, 0, 0, null);
                        g.dispose();

                        scaled.setIcon(new ImageIcon(bw));
                    }
                };
                brighten.addChangeListener(cl);

                images.add(new JLabel(new ImageIcon(colorImage)));
                images.add(scaled);
                images.add(new JLabel(new ImageIcon(grayImage)));
                images.add(new JLabel(new ImageIcon(blackAndWhiteImage)));

                JOptionPane.showMessageDialog(null, gui);
            }
        };
        // Swing GUIs should be created and updated on the EDT
        // http://docs.oracle.com/javase/tutorial/uiswing/concurrency/initial.html
        SwingUtilities.invokeLater(r);
    }
}

Answer 3

您实现的效果不是通过预定义阈值的二值化，而是通过一种称为抖动的技术完成的。许多抖动方法通过传播误差（当前图像中的强度 - 给定点的二进制输出）来工作，从而调整下一个输出。这样做是为了创建一种视觉效果，如果您不仔细看的话，结果图像可能看起来不是黑白的。

Floyd-Steinberg 提出了这样一个简单而著名的方法，它的伪代码是：

for y := 1 to image height
    for x := 1 to image width
        v := im(y, x)
        if v < 128 then
            result(y, x) := 0
        else
            result(y, x) := 255
        error := v - result(y, x)
        propagate_error(im, y, x, error)

此方法的propagate_error 可以指定为（不考虑边界情况）：

    im(y,   x+1) := im(y,   x+1) + (7/16) * error
    im(y+1, x+1) := im(y+1, x+1) + (1/16) * error
    im(y+1, x  ) := im(y+1, x  ) + (5/16) * error
    im(y+1, x-1) := im(y+1, x-1) + (3/16) * error

考虑到给出的伪代码的直接实现，右下图是左图的二进制版本。右边的图像实际上只有黑白两种颜色，这对于知道这种方法的人来说是一件小事，但对于那些不知道这种方法的人来说，这似乎是不可能的。创建的图案给人的印象是有几种灰色调，具体取决于您从远处看图像。

Answer 4

-试试下面的简单代码，

 package com.bethecoder.tutorials.imageio;

import java.awt.Graphics2D;
import java.awt.image.BufferedImage;
import java.io.File;
import java.io.IOException;

import javax.imageio.ImageIO;

public class BlackAndWhiteTest {

  /**
   * @param args
   * @throws IOException 
   */
  public static void main(String[] args) throws IOException {

    File file = new File("C:/Temp/stpatricks_08.gif");
    BufferedImage orginalImage = ImageIO.read(file);

    BufferedImage blackAndWhiteImg = new BufferedImage(
        orginalImage.getWidth(), orginalImage.getHeight(),
        BufferedImage.TYPE_BYTE_BINARY);

    Graphics2D graphics = blackAndWhiteImg.createGraphics();
    graphics.drawImage(orginalImage, 0, 0, null);

    ImageIO.write(blackAndWhiteImg, "png", new File("c:/Temp/stpatricks_08_bw.png")); 
  }

}