JavaOpenCV学习笔记（1）：环境配置与图片读取展示

环境配置

首先到官网下载 OpenCV。

解压后，进入 /build/java 目录，将 jar 包和对应系统版本的 dll 复制到项目中。

把 jar 包添加到构建路径，然后在 vm 参数中加入 -Djava.library.path=$PROJECT_DIR$\lib\opencv 完成环境配置。

使用 《OpenCV 3.0 Computer Vision with Java》 中的例子来测试环境是否配置成功：

package opencv;

import org.opencv.core.Core;
import org.opencv.core.CvType;
import org.opencv.core.Mat;
import org.opencv.core.Scalar;

/**
 * @author yuan
 * @version 1.0
 * @date 2020/5/11 14:47
 */
public class SimpleSample {
    static {
        System.loadLibrary(Core.NATIVE_LIBRARY_NAME);
    }

    public static void main(String[] args) {
        System.out.println("Welcome to OpenCV " + Core.VERSION);
        Mat m = new Mat(5, 10, CvType.CV_8UC1, new Scalar(0));
        System.out.println("OpenCV Mat: " + m);
        Mat mr1 = m.row(1);
        mr1.setTo(new Scalar(1));
        Mat mc5 = m.col(5);
        mc5.setTo(new Scalar(5));
        System.out.println("OpenCV Mat data:\n" + m.dump());
    }
}

运行结果：

Welcome to OpenCV 4.3.0
OpenCV Mat: Mat [ 5*10*CV_8UC1, isCont=true, isSubmat=false, nativeObj=0x1410e70, dataAddr=0x1470080 ]
OpenCV Mat data:
[  0,   0,   0,   0,   0,   5,   0,   0,   0,   0;
   1,   1,   1,   1,   1,   5,   1,   1,   1,   1;
   0,   0,   0,   0,   0,   5,   0,   0,   0,   0;
   0,   0,   0,   0,   0,   5,   0,   0,   0,   0;
   0,   0,   0,   0,   0,   5,   0,   0,   0,   0]

说明环境配置成功。

图片读取

使用 Imgcodecs.imread(String fileName) 或 Imgcodecs.imread(String fileName, int readMod) 即可完成图片读取。

public class ImageRead {
    private static final String IMAGE_PATH = "D:/test/Amiya.jpg";

    static {
        System.loadLibrary(Core.NATIVE_LIBRARY_NAME);
    }

    public static void main(String[] args) {
        // 读取灰度图
        Mat amiya = Imgcodecs.imread(IMAGE_PATH, Imgcodecs.IMREAD_GRAYSCALE);
        System.out.println(amiya.width());
        System.out.println(amiya.height());
    }
}

查看 Imgcodecs 的源码可知，读取模式有这些：

// C++: enum ImreadModes
public static final int
            IMREAD_UNCHANGED = -1,
            IMREAD_GRAYSCALE = 0,
            IMREAD_COLOR = 1,
            IMREAD_ANYDEPTH = 2,
            IMREAD_ANYCOLOR = 4,
            IMREAD_LOAD_GDAL = 8,
            IMREAD_REDUCED_GRAYSCALE_2 = 16,
            IMREAD_REDUCED_COLOR_2 = 17,
            IMREAD_REDUCED_GRAYSCALE_4 = 32,
            IMREAD_REDUCED_COLOR_4 = 33,
            IMREAD_REDUCED_GRAYSCALE_8 = 64,
            IMREAD_REDUCED_COLOR_8 = 65,
            IMREAD_IGNORE_ORIENTATION = 128;

看起来和 python 中的 cv2 库差不多。

图片展示

旧版本的 OpenCV 没有为 java 提供图片展示功能，新版本可以使用 HighGui.imshow 来展示图片，调用 imshow 后必须使用 HighGui.waitKey 进行阻塞。

我们也可以用 swing 自己写一个图片展示器。

《OpenCV 3.0 Computer Vision with Java》 中提供了一个 ImageViewer 类，对它稍加改造：

package utils;

import org.opencv.core.Mat;

import javax.swing.*;
import java.awt.*;
import java.awt.image.BufferedImage;
import java.awt.image.DataBufferByte;

/**
 * @author yuan
 * @version 1.0
 * @date 2020/5/11 16:18
 */
public class ImageViewer {
    private JLabel imageView;
    private JFrame windowFrame;

    public ImageViewer(Mat image, String windowName) {
        setSystemLookAndFeel();
        createJFrame(image, windowName);
    }

    public ImageViewer(Mat image, String windowName, boolean show) {
        this(image, windowName);
        if (show) {
            this.show();
        }
    }

    public void show() {
        this.windowFrame.setVisible(true);
    }

    public void hide() {
        this.windowFrame.setVisible(false);
    }

    private void createJFrame(Mat image, String windowName) {
        this.imageView = new JLabel();
        this.windowFrame = new JFrame(windowName);
        this.windowFrame.add(this.imageView, BorderLayout.CENTER);
        this.windowFrame.setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
        Image loadedImage = toBufferedImage(image);
        this.imageView.setIcon(new ImageIcon(loadedImage));
        this.windowFrame.pack();
        this.windowFrame.setLocationRelativeTo(null);
    }

    private void setSystemLookAndFeel() {
        try {
            UIManager.setLookAndFeel
                    (UIManager.getSystemLookAndFeelClassName());
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        } catch (InstantiationException e) {
            e.printStackTrace();
        } catch (IllegalAccessException e) {
            e.printStackTrace();
        } catch (UnsupportedLookAndFeelException e) {
            e.printStackTrace();
        }
    }

    public Image toBufferedImage(Mat matrix) {
        int type = BufferedImage.TYPE_BYTE_GRAY;
        if (matrix.channels() > 1) {
            type = BufferedImage.TYPE_3BYTE_BGR;
        }
        int bufferSize = matrix.channels() * matrix.cols() * matrix.rows();
        byte[] buffer = new byte[bufferSize];
        matrix.get(0, 0, buffer);
        BufferedImage image = new BufferedImage(matrix.cols(), matrix.
                rows(), type);
        final byte[] targetPixels = ((DataBufferByte) image.getRaster().
                getDataBuffer()).getData();
        System.arraycopy(buffer, 0, targetPixels, 0, buffer.length);
        return image;
    }
}

测试：

ImageViewer imageViewer = new ImageViewer(amiya, "小驴子", true);

运行结果：