[OpenCV] Samples 08: edge

Canny edge detector

效率高，效果可控。

• TrackBar的使用。
• 技巧：gray找边缘后作为mask去CopyTo()。

#include "opencv2/core/utility.hpp"
#include "opencv2/imgproc.hpp"
#include "opencv2/imgcodecs.hpp"
#include "opencv2/highgui.hpp"

#include <stdio.h>

using namespace cv;
using namespace std;

int edgeThresh = 1;
Mat image, gray, edge, cedge;

// define a trackbar callback
static void onTrackbar(int, void*)
{
    /* Step one */
    blur(gray, edge, Size(3,3));

    // Run the edge detector on grayscale
    Canny(edge, edge, edgeThresh, edgeThresh*3, 3);
    cedge = Scalar::all(0);

    /*
     * Jeff --> the second parameter is mask.
     */
    image.copyTo(cedge, edge);
    imshow("Edge map", cedge);
}

static void help()
{
    printf("\nThis sample demonstrates Canny edge detection\n"
           "Call:\n"
           "    /.edge [image_name -- Default is ../data/fruits.jpg]\n\n");
}

const char* keys =
{
    "{help h||}{@image |../data/fruits.jpg|input image name}"
};

int main( int argc, const char** argv )
{
    CommandLineParser parser(argc, argv, keys);
    if (parser.has("help"))
    {
        help();
        return 0;
    }
    string filename = parser.get<string>(0);

    image = imread(filename, 1);
    if(image.empty())
    {
        printf("Cannot read image file: %s\n", filename.c_str());
        help();
        return -1;
    }
    cedge.create(image.size(), image.type());
    cvtColor(image, gray, COLOR_BGR2GRAY);

    // Create a window
    namedWindow("Edge map", 1);

    // create a toolbar
    createTrackbar("Canny threshold", "Edge map", &edgeThresh, 100, onTrackbar);

    // Show the image
    onTrackbar(0, 0);

    // Wait for a key stroke; the same function arranges events processing
    waitKey(0);

    return 0;
}