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使用 inRange 的阈值处理操作

Threshold_inRange_HSV_colorspace.jpg Threshold_inRange_RGB_colorspace.jpg

本教程中你将学到如何：

  • 使用 OpenCV 的 cv::inRange 函数执行基本的阈值处理（thresholding）操作。
  • 基于 HSV 色彩空间中像素值的范围来检测物体。

理论

Section titled “理论”
  • 在之前的教程中，我们学习了如何使用 cv::threshold 函数进行阈值处理。
  • 在本教程中，我们将学习如何使用 cv::inRange 函数来实现。
  • 概念保持不变，只是现在我们增加了一个所需的像素值范围。

HSV 色彩空间

Section titled “HSV 色彩空间”

HSV（hue，色相；saturation，饱和度；value，明度）色彩空间是一种与 RGB 颜色模型类似的色彩空间表示模型。由于色相（hue）通道对颜色类型建模，它在需要基于颜色分割物体的图像处理任务中非常有用。饱和度（saturation）的变化从不饱和（表示灰色梯度）到完全饱和（无白色分量）。明度（value）通道描述颜色的亮度或强度。

由于 RGB 色彩空间中的颜色使用三个通道编码，基于颜色来分割图像中的物体会更加困难。

使用 cv::cvtColor 函数在色彩空间之间进行转换的公式，可参见色彩空间转换（Color Space Conversions）相关文档。

代码

Section titled “代码”

C++

教程代码如下所示。你也可以从此处下载。

#include "opencv2/imgproc.hpp"
#include "opencv2/highgui.hpp"
#include "opencv2/videoio.hpp"
#include <iostream>


using namespace cv;


/** Global Variables */
const int max_value_H = 360/2;
const int max_value = 255;
const String window_capture_name = "Video Capture";
const String window_detection_name = "Object Detection";
int low_H = 0, low_S = 0, low_V = 0;
int high_H = max_value_H, high_S = max_value, high_V = max_value;


static void on_low_H_thresh_trackbar(int, void *)
{
    low_H = min(high_H-1, low_H);
    setTrackbarPos("Low H", window_detection_name, low_H);
}


static void on_high_H_thresh_trackbar(int, void *)
{
    high_H = max(high_H, low_H+1);
    setTrackbarPos("High H", window_detection_name, high_H);
}


static void on_low_S_thresh_trackbar(int, void *)
{
    low_S = min(high_S-1, low_S);
    setTrackbarPos("Low S", window_detection_name, low_S);
}


static void on_high_S_thresh_trackbar(int, void *)
{
    high_S = max(high_S, low_S+1);
    setTrackbarPos("High S", window_detection_name, high_S);
}


static void on_low_V_thresh_trackbar(int, void *)
{
    low_V = min(high_V-1, low_V);
    setTrackbarPos("Low V", window_detection_name, low_V);
}


static void on_high_V_thresh_trackbar(int, void *)
{
    high_V = max(high_V, low_V+1);
    setTrackbarPos("High V", window_detection_name, high_V);
}


int main(int argc, char* argv[])
{
    VideoCapture cap(argc > 1 ? atoi(argv[1]) : 0);


    namedWindow(window_capture_name);
    namedWindow(window_detection_name);


    // Trackbars to set thresholds for HSV values
    createTrackbar("Low H", window_detection_name, &low_H, max_value_H, on_low_H_thresh_trackbar);
    createTrackbar("High H", window_detection_name, &high_H, max_value_H, on_high_H_thresh_trackbar);
    createTrackbar("Low S", window_detection_name, &low_S, max_value, on_low_S_thresh_trackbar);
    createTrackbar("High S", window_detection_name, &high_S, max_value, on_high_S_thresh_trackbar);
    createTrackbar("Low V", window_detection_name, &low_V, max_value, on_low_V_thresh_trackbar);
    createTrackbar("High V", window_detection_name, &high_V, max_value, on_high_V_thresh_trackbar);


    Mat frame, frame_HSV, frame_threshold;
    while (true) {
        cap >> frame;
        if(frame.empty())
        {
            break;
        }


        // Convert from BGR to HSV colorspace
        cvtColor(frame, frame_HSV, COLOR_BGR2HSV);
        // Detect the object based on HSV Range Values
        inRange(frame_HSV, Scalar(low_H, low_S, low_V), Scalar(high_H, high_S, high_V), frame_threshold);


        // Show the frames
        imshow(window_capture_name, frame);
        imshow(window_detection_name, frame_threshold);


        char key = (char) waitKey(30);
        if (key == 'q' || key == 27)
        {
            break;
        }
    }
    return 0;
}

Java

教程代码如下所示。你也可以从此处下载。

import java.awt.BorderLayout;
import java.awt.Container;
import java.awt.Image;
import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;
import java.util.List;


import javax.swing.BoxLayout;
import javax.swing.ImageIcon;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JSlider;
import javax.swing.SwingWorker;
import javax.swing.event.ChangeEvent;
import javax.swing.event.ChangeListener;


import org.opencv.core.Core;
import org.opencv.core.Mat;
import org.opencv.core.Scalar;
import org.opencv.highgui.HighGui;
import org.opencv.imgproc.Imgproc;
import org.opencv.videoio.VideoCapture;


public class ThresholdInRange {
    private static int MAX_VALUE = 255;
    private static int MAX_VALUE_H = 360/2;
    private static final String WINDOW_NAME = "Thresholding Operations using inRange demo";
    private static final String LOW_H_NAME = "Low H";
    private static final String LOW_S_NAME = "Low S";
    private static final String LOW_V_NAME = "Low V";
    private static final String HIGH_H_NAME = "High H";
    private static final String HIGH_S_NAME = "High S";
    private static final String HIGH_V_NAME = "High V";
    private JSlider sliderLowH;
    private JSlider sliderHighH;
    private JSlider sliderLowS;
    private JSlider sliderHighS;
    private JSlider sliderLowV;
    private JSlider sliderHighV;
    private VideoCapture cap;
    private Mat matFrame = new Mat();
    private JFrame frame;
    private JLabel imgCaptureLabel;
    private JLabel imgDetectionLabel;
    private CaptureTask captureTask;


    public ThresholdInRange(String[] args) {
        int cameraDevice = 0;
        if (args.length > 0) {
            cameraDevice = Integer.parseInt(args[0]);
        }
        cap = new VideoCapture(cameraDevice);
        if (!cap.isOpened()) {
            System.err.println("Cannot open camera: " + cameraDevice);
            System.exit(0);
        }
        if (!cap.read(matFrame)) {
            System.err.println("Cannot read camera stream.");
            System.exit(0);
        }


        // Create and set up the window.
        frame = new JFrame(WINDOW_NAME);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.addWindowListener(new WindowAdapter() {
            @Override
            public void windowClosing(WindowEvent windowEvent) {
                captureTask.cancel(true);
            }
        });
        // Set up the content pane.
        Image img = HighGui.toBufferedImage(matFrame);
        addComponentsToPane(frame.getContentPane(), img);
        // Use the content pane's default BorderLayout. No need for
        // setLayout(new BorderLayout());
        // Display the window.
        frame.pack();
        frame.setVisible(true);


        captureTask = new CaptureTask();
        captureTask.execute();
    }


    private class CaptureTask extends SwingWorker<Void, Mat> {
        @Override
        protected Void doInBackground() {
            Mat matFrame = new Mat();


            while (!isCancelled()) {
                if (!cap.read(matFrame)) {
                    break;
                }
                publish(matFrame.clone());
            }
            return null;
        }


        @Override
        protected void process(List<Mat> frames) {
            Mat frame = frames.get(frames.size() - 1);
            Mat frameHSV = new Mat();
            Imgproc.cvtColor(frame, frameHSV, Imgproc.COLOR_BGR2HSV);
            Mat thresh = new Mat();
            Core.inRange(frameHSV, new Scalar(sliderLowH.getValue(), sliderLowS.getValue(), sliderLowV.getValue()),
                    new Scalar(sliderHighH.getValue(), sliderHighS.getValue(), sliderHighV.getValue()), thresh);
            update(frame, thresh);
        }
    }


    private void addComponentsToPane(Container pane, Image img) {
        if (!(pane.getLayout() instanceof BorderLayout)) {
            pane.add(new JLabel("Container doesn't use BorderLayout!"));
            return;
        }


        JPanel sliderPanel = new JPanel();
        sliderPanel.setLayout(new BoxLayout(sliderPanel, BoxLayout.PAGE_AXIS));


        sliderPanel.add(new JLabel(LOW_H_NAME));
        sliderLowH = new JSlider(0, MAX_VALUE_H, 0);
        sliderLowH.setMajorTickSpacing(50);
        sliderLowH.setMinorTickSpacing(10);
        sliderLowH.setPaintTicks(true);
        sliderLowH.setPaintLabels(true);
        sliderPanel.add(sliderLowH);


        sliderPanel.add(new JLabel(HIGH_H_NAME));
        sliderHighH = new JSlider(0, MAX_VALUE_H, MAX_VALUE_H);
        sliderHighH.setMajorTickSpacing(50);
        sliderHighH.setMinorTickSpacing(10);
        sliderHighH.setPaintTicks(true);
        sliderHighH.setPaintLabels(true);
        sliderPanel.add(sliderHighH);


        sliderPanel.add(new JLabel(LOW_S_NAME));
        sliderLowS = new JSlider(0, MAX_VALUE, 0);
        sliderLowS.setMajorTickSpacing(50);
        sliderLowS.setMinorTickSpacing(10);
        sliderLowS.setPaintTicks(true);
        sliderLowS.setPaintLabels(true);
        sliderPanel.add(sliderLowS);


        sliderPanel.add(new JLabel(HIGH_S_NAME));
        sliderHighS = new JSlider(0, MAX_VALUE, MAX_VALUE);
        sliderHighS.setMajorTickSpacing(50);
        sliderHighS.setMinorTickSpacing(10);
        sliderHighS.setPaintTicks(true);
        sliderHighS.setPaintLabels(true);
        sliderPanel.add(sliderHighS);


        sliderPanel.add(new JLabel(LOW_V_NAME));
        sliderLowV = new JSlider(0, MAX_VALUE, 0);
        sliderLowV.setMajorTickSpacing(50);
        sliderLowV.setMinorTickSpacing(10);
        sliderLowV.setPaintTicks(true);
        sliderLowV.setPaintLabels(true);
        sliderPanel.add(sliderLowV);


        sliderPanel.add(new JLabel(HIGH_V_NAME));
        sliderHighV = new JSlider(0, MAX_VALUE, MAX_VALUE);
        sliderHighV.setMajorTickSpacing(50);
        sliderHighV.setMinorTickSpacing(10);
        sliderHighV.setPaintTicks(true);
        sliderHighV.setPaintLabels(true);
        sliderPanel.add(sliderHighV);


        sliderLowH.addChangeListener(new ChangeListener() {
            @Override
            public void stateChanged(ChangeEvent e) {
                JSlider source = (JSlider) e.getSource();
                int valH = Math.min(sliderHighH.getValue()-1, source.getValue());
                sliderLowH.setValue(valH);
            }
        });
        sliderHighH.addChangeListener(new ChangeListener() {
            @Override
            public void stateChanged(ChangeEvent e) {
                JSlider source = (JSlider) e.getSource();
                int valH = Math.max(source.getValue(), sliderLowH.getValue()+1);
                sliderHighH.setValue(valH);
            }
        });
        sliderLowS.addChangeListener(new ChangeListener() {
            @Override
            public void stateChanged(ChangeEvent e) {
                JSlider source = (JSlider) e.getSource();
                int valS = Math.min(sliderHighS.getValue()-1, source.getValue());
                sliderLowS.setValue(valS);
            }
        });
        sliderHighS.addChangeListener(new ChangeListener() {
            @Override
            public void stateChanged(ChangeEvent e) {
                JSlider source = (JSlider) e.getSource();
                int valS = Math.max(source.getValue(), sliderLowS.getValue()+1);
                sliderHighS.setValue(valS);
            }
        });
        sliderLowV.addChangeListener(new ChangeListener() {
            @Override
            public void stateChanged(ChangeEvent e) {
                JSlider source = (JSlider) e.getSource();
                int valV = Math.min(sliderHighV.getValue()-1, source.getValue());
                sliderLowV.setValue(valV);
            }
        });
        sliderHighV.addChangeListener(new ChangeListener() {
            @Override
            public void stateChanged(ChangeEvent e) {
                JSlider source = (JSlider) e.getSource();
                int valV = Math.max(source.getValue(), sliderLowV.getValue()+1);
                sliderHighV.setValue(valV);
            }
        });


        pane.add(sliderPanel, BorderLayout.PAGE_START);
        JPanel framePanel = new JPanel();
        imgCaptureLabel = new JLabel(new ImageIcon(img));
        framePanel.add(imgCaptureLabel);
        imgDetectionLabel = new JLabel(new ImageIcon(img));
        framePanel.add(imgDetectionLabel);
        pane.add(framePanel, BorderLayout.CENTER);
    }


    private void update(Mat imgCapture, Mat imgThresh) {
        imgCaptureLabel.setIcon(new ImageIcon(HighGui.toBufferedImage(imgCapture)));
        imgDetectionLabel.setIcon(new ImageIcon(HighGui.toBufferedImage(imgThresh)));
        frame.repaint();
    }


    public static void main(String[] args) {
        // Load the native OpenCV library
        System.loadLibrary(Core.NATIVE_LIBRARY_NAME);


        // Schedule a job for the event dispatch thread:
        // creating and showing this application's GUI.
        javax.swing.SwingUtilities.invokeLater(new Runnable() {
            @Override
            public void run() {
                new ThresholdInRange(args);
            }
        });
    }
}

Python

教程代码如下所示。你也可以从此处下载。

from __future__ import print_function
import cv2 as cv
import argparse


max_value = 255
max_value_H = 360//2
low_H = 0
low_S = 0
low_V = 0
high_H = max_value_H
high_S = max_value
high_V = max_value
window_capture_name = 'Video Capture'
window_detection_name = 'Object Detection'
low_H_name = 'Low H'
low_S_name = 'Low S'
low_V_name = 'Low V'
high_H_name = 'High H'
high_S_name = 'High S'
high_V_name = 'High V'


def on_low_H_thresh_trackbar(val):
    global low_H
    global high_H
    low_H = val
    low_H = min(high_H-1, low_H)
    cv.setTrackbarPos(low_H_name, window_detection_name, low_H)


def on_high_H_thresh_trackbar(val):
    global low_H
    global high_H
    high_H = val
    high_H = max(high_H, low_H+1)
    cv.setTrackbarPos(high_H_name, window_detection_name, high_H)


def on_low_S_thresh_trackbar(val):
    global low_S
    global high_S
    low_S = val
    low_S = min(high_S-1, low_S)
    cv.setTrackbarPos(low_S_name, window_detection_name, low_S)


def on_high_S_thresh_trackbar(val):
    global low_S
    global high_S
    high_S = val
    high_S = max(high_S, low_S+1)
    cv.setTrackbarPos(high_S_name, window_detection_name, high_S)


def on_low_V_thresh_trackbar(val):
    global low_V
    global high_V
    low_V = val
    low_V = min(high_V-1, low_V)
    cv.setTrackbarPos(low_V_name, window_detection_name, low_V)


def on_high_V_thresh_trackbar(val):
    global low_V
    global high_V
    high_V = val
    high_V = max(high_V, low_V+1)
    cv.setTrackbarPos(high_V_name, window_detection_name, high_V)


parser = argparse.ArgumentParser(description='Code for Thresholding Operations using inRange tutorial.')
parser.add_argument('--camera', help='Camera divide number.', default=0, type=int)
args = parser.parse_args()


cap = cv.VideoCapture(args.camera)


cv.namedWindow(window_capture_name)
cv.namedWindow(window_detection_name)


cv.createTrackbar(low_H_name, window_detection_name , low_H, max_value_H, on_low_H_thresh_trackbar)
cv.createTrackbar(high_H_name, window_detection_name , high_H, max_value_H, on_high_H_thresh_trackbar)
cv.createTrackbar(low_S_name, window_detection_name , low_S, max_value, on_low_S_thresh_trackbar)
cv.createTrackbar(high_S_name, window_detection_name , high_S, max_value, on_high_S_thresh_trackbar)
cv.createTrackbar(low_V_name, window_detection_name , low_V, max_value, on_low_V_thresh_trackbar)
cv.createTrackbar(high_V_name, window_detection_name , high_V, max_value, on_high_V_thresh_trackbar)


while True:
    ret, frame = cap.read()
    if frame is None:
        break


    frame_HSV = cv.cvtColor(frame, cv.COLOR_BGR2HSV)
    frame_threshold = cv.inRange(frame_HSV, (low_H, low_S, low_V), (high_H, high_S, high_V))


    cv.imshow(window_capture_name, frame)
    cv.imshow(window_detection_name, frame_threshold)


    key = cv.waitKey(30)
    if key == ord('q') or key == 27:
        break

说明

Section titled “说明”

让我们看一下程序的整体结构：

  • 从默认的或指定的采集设备捕获视频流：

    C++

    VideoCapture cap(argc > 1 ? atoi(argv[1]) : 0);

    Java

    cap = new VideoCapture(cameraDevice);

    Python

    cap = cv.VideoCapture(args.camera)

  • 创建窗口，用于显示原始画面和阈值处理后的画面：

    C++

    namedWindow(window_capture_name);
    namedWindow(window_detection_name);

    Java

    // Create and set up the window.
    frame = new JFrame(WINDOW_NAME);
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.addWindowListener(new WindowAdapter() {
        @Override
        public void windowClosing(WindowEvent windowEvent) {
            captureTask.cancel(true);
        }
    });
    // Set up the content pane.
    Image img = HighGui.toBufferedImage(matFrame);
    addComponentsToPane(frame.getContentPane(), img);
    // Use the content pane's default BorderLayout. No need for
    // setLayout(new BorderLayout());
    // Display the window.
    frame.pack();
    frame.setVisible(true);

    Python

    cv.namedWindow(window_capture_name)
    cv.namedWindow(window_detection_name)

  • 创建用于设置 HSV 值范围的 Trackbar（滑动条）：

    C++

    // Trackbars to set thresholds for HSV values
    createTrackbar("Low H", window_detection_name, &low_H, max_value_H, on_low_H_thresh_trackbar);
    createTrackbar("High H", window_detection_name, &high_H, max_value_H, on_high_H_thresh_trackbar);
    createTrackbar("Low S", window_detection_name, &low_S, max_value, on_low_S_thresh_trackbar);
    createTrackbar("High S", window_detection_name, &high_S, max_value, on_high_S_thresh_trackbar);
    createTrackbar("Low V", window_detection_name, &low_V, max_value, on_low_V_thresh_trackbar);
    createTrackbar("High V", window_detection_name, &high_V, max_value, on_high_V_thresh_trackbar);

    Java

    sliderPanel.add(new JLabel(LOW_H_NAME));
    sliderLowH = new JSlider(0, MAX_VALUE_H, 0);
    sliderLowH.setMajorTickSpacing(50);
    sliderLowH.setMinorTickSpacing(10);
    sliderLowH.setPaintTicks(true);
    sliderLowH.setPaintLabels(true);
    sliderPanel.add(sliderLowH);
    

    sliderPanel.add(new JLabel(HIGH_H_NAME));
    sliderHighH = new JSlider(0, MAX_VALUE_H, MAX_VALUE_H);
    sliderHighH.setMajorTickSpacing(50);
    sliderHighH.setMinorTickSpacing(10);
    sliderHighH.setPaintTicks(true);
    sliderHighH.setPaintLabels(true);
    sliderPanel.add(sliderHighH);
    

    sliderPanel.add(new JLabel(LOW_S_NAME));
    sliderLowS = new JSlider(0, MAX_VALUE, 0);
    sliderLowS.setMajorTickSpacing(50);
    sliderLowS.setMinorTickSpacing(10);
    sliderLowS.setPaintTicks(true);
    sliderLowS.setPaintLabels(true);
    sliderPanel.add(sliderLowS);
    

    sliderPanel.add(new JLabel(HIGH_S_NAME));
    sliderHighS = new JSlider(0, MAX_VALUE, MAX_VALUE);
    sliderHighS.setMajorTickSpacing(50);
    sliderHighS.setMinorTickSpacing(10);
    sliderHighS.setPaintTicks(true);
    sliderHighS.setPaintLabels(true);
    sliderPanel.add(sliderHighS);
    

    sliderPanel.add(new JLabel(LOW_V_NAME));
    sliderLowV = new JSlider(0, MAX_VALUE, 0);
    sliderLowV.setMajorTickSpacing(50);
    sliderLowV.setMinorTickSpacing(10);
    sliderLowV.setPaintTicks(true);
    sliderLowV.setPaintLabels(true);
    sliderPanel.add(sliderLowV);
    

    sliderPanel.add(new JLabel(HIGH_V_NAME));
    sliderHighV = new JSlider(0, MAX_VALUE, MAX_VALUE);
    sliderHighV.setMajorTickSpacing(50);
    sliderHighV.setMinorTickSpacing(10);
    sliderHighV.setPaintTicks(true);
    sliderHighV.setPaintLabels(true);
    sliderPanel.add(sliderHighV);

    Python

    cv.createTrackbar(low_H_name, window_detection_name , low_H, max_value_H, on_low_H_thresh_trackbar)
    cv.createTrackbar(high_H_name, window_detection_name , high_H, max_value_H, on_high_H_thresh_trackbar)
    cv.createTrackbar(low_S_name, window_detection_name , low_S, max_value, on_low_S_thresh_trackbar)
    cv.createTrackbar(high_S_name, window_detection_name , high_S, max_value, on_high_S_thresh_trackbar)
    cv.createTrackbar(low_V_name, window_detection_name , low_V, max_value, on_low_V_thresh_trackbar)
    cv.createTrackbar(high_V_name, window_detection_name , high_V, max_value, on_high_V_thresh_trackbar)

  • 在用户希望退出程序之前，反复执行以下操作：

    C++

    cap >> frame;
    if(frame.empty())
    {
        break;
    }
    

    // Convert from BGR to HSV colorspace
    cvtColor(frame, frame_HSV, COLOR_BGR2HSV);
    // Detect the object based on HSV Range Values
    inRange(frame_HSV, Scalar(low_H, low_S, low_V), Scalar(high_H, high_S, high_V), frame_threshold);

    Java

    private class CaptureTask extends SwingWorker<Void, Mat> {
        @Override
        protected Void doInBackground() {
            Mat matFrame = new Mat();
    

            while (!isCancelled()) {
                if (!cap.read(matFrame)) {
                    break;
                }
                publish(matFrame.clone());
            }
            return null;
        }
    

        @Override
        protected void process(List<Mat> frames) {
            Mat frame = frames.get(frames.size() - 1);
            Mat frameHSV = new Mat();
            Imgproc.cvtColor(frame, frameHSV, Imgproc.COLOR_BGR2HSV);
            Mat thresh = new Mat();
            Core.inRange(frameHSV, new Scalar(sliderLowH.getValue(), sliderLowS.getValue(), sliderLowV.getValue()),
                    new Scalar(sliderHighH.getValue(), sliderHighS.getValue(), sliderHighV.getValue()), thresh);
            update(frame, thresh);
        }
    }

    Python

    ret, frame = cap.read()
    if frame is None:
        break
    

    frame_HSV = cv.cvtColor(frame, cv.COLOR_BGR2HSV)
    frame_threshold = cv.inRange(frame_HSV, (low_H, low_S, low_V), (high_H, high_S, high_V))

  • 显示图像：

    C++

    // Show the frames
    imshow(window_capture_name, frame);
    imshow(window_detection_name, frame_threshold);

    Java

    imgCaptureLabel.setIcon(new ImageIcon(HighGui.toBufferedImage(imgCapture)));
    imgDetectionLabel.setIcon(new ImageIcon(HighGui.toBufferedImage(imgThresh)));
    frame.repaint();

    Python

    cv.imshow(window_capture_name, frame)
    cv.imshow(window_detection_name, frame_threshold)

  • 对于控制下限范围的 Trackbar，例如色相（hue）值：

    C++

    static void on_low_H_thresh_trackbar(int, void *)
    {
        low_H = min(high_H-1, low_H);
        setTrackbarPos("Low H", window_detection_name, low_H);
    }

    Java

    sliderLowH.addChangeListener(new ChangeListener() {
        @Override
        public void stateChanged(ChangeEvent e) {
            JSlider source = (JSlider) e.getSource();
            int valH = Math.min(sliderHighH.getValue()-1, source.getValue());
            sliderLowH.setValue(valH);
        }
    });

    Python

    def on_low_H_thresh_trackbar(val):
        global low_H
        global high_H
        low_H = val
        low_H = min(high_H-1, low_H)
        cv.setTrackbarPos(low_H_name, window_detection_name, low_H)

  • 对于控制上限范围的 Trackbar，例如色相（hue）值：

    C++

    static void on_high_H_thresh_trackbar(int, void *)
    {
        high_H = max(high_H, low_H+1);
        setTrackbarPos("High H", window_detection_name, high_H);
    }

    Java

    sliderHighH.addChangeListener(new ChangeListener() {
        @Override
        public void stateChanged(ChangeEvent e) {
            JSlider source = (JSlider) e.getSource();
            int valH = Math.max(source.getValue(), sliderLowH.getValue()+1);
            sliderHighH.setValue(valH);
        }
    });

    Python

    def on_high_H_thresh_trackbar(val):
        global low_H
        global high_H
        high_H = val
        high_H = max(high_H, low_H+1)
        cv.setTrackbarPos(high_H_name, window_detection_name, high_H)

  • 求出最大值和最小值是必要的，以避免出现阈值上限变得小于阈值下限之类的矛盾。

结果

Section titled “结果”

Threshold_inRange_Tutorial_Result_input.jpeg Threshold_inRange_Tutorial_Result_output.jpeg

  • 编译本程序后，运行它。程序将打开两个窗口。

  • 当你通过 Trackbar 设置范围值时，处理结果画面会显示在另一个窗口中。