c++ - 来自相机的裁剪图像无法正常工作

Question

我正在使用 openCV 捕获并保存固定大小的输出图像 (92 x 112)。它将捕获视频帧并裁剪它们。但是，输出图像没有显示正确的大小(有时是 147 x 147、140 x 140 ...)。我的代码有什么问题。有crop image code和whole code。提前致谢

裁剪图片

crop = frame(roi_b);
resize(crop, res, Size(92, 112), 0, 0, INTER_LINEAR); // This will be needed later while saving images        

cvtColor(crop, gray, CV_BGR2GRAY); // Convert cropped image to Grayscale

看完整代码看参数含义

#include "opencv2/objdetect/objdetect.hpp"
#include "opencv2/highgui/highgui.hpp"
#include "opencv2/imgproc/imgproc.hpp"

#include <iostream>
#include <stdio.h>

using namespace std;
using namespace cv;

// Function Headers
void detectAndDisplay(Mat frame);

// Global variables
// Copy this file from opencv/data/haarscascades to target folder
string face_cascade_name = "haarcascade_frontalface_alt.xml";
CascadeClassifier face_cascade;
string window_name = "Capture - Face detection";
int filenumber; // Number of file to be saved
string filename;

// Function main
int main(void)
{
    VideoCapture capture(0);

    if (!capture.isOpened())  // check if we succeeded
        return -1;

    // Load the cascade
    if (!face_cascade.load(face_cascade_name))
    {
        printf("--(!)Error loading\n");
        return (-1);
    };

    // Read the video stream
    Mat frame;

    for (;;)
    {
        capture >> frame;

        // Apply the classifier to the frame
        if (!frame.empty())
        {
            detectAndDisplay(frame);
        }
        else
        {
            printf(" --(!) No captured frame -- Break!");
            break;
        }

        int c = waitKey(10);

        if (27 == char(c))
        {
            break;
        }
    }

    return 0;
}

// Function detectAndDisplay
void detectAndDisplay(Mat frame)
{
    std::vector<Rect> faces;
    Mat frame_gray;
    Mat crop;
    Mat res;
    Mat gray;
    string text;
    stringstream sstm;

    cvtColor(frame, frame_gray, COLOR_BGR2GRAY);
    equalizeHist(frame_gray, frame_gray);

// Detect faces
    face_cascade.detectMultiScale(frame_gray, faces, 1.1, 2, 0 | CASCADE_SCALE_IMAGE, Size(30, 30));

// Set Region of Interest
    cv::Rect roi_b;
    cv::Rect roi_c;

    size_t ic = 0; // ic is index of current element
    int ac = 0; // ac is area of current element

    size_t ib = 0; // ib is index of biggest element
    int ab = 0; // ab is area of biggest element

    for (ic = 0; ic < faces.size(); ic++) // Iterate through all current elements (detected faces)

    {
        roi_c.x = faces[ic].x;
        roi_c.y = faces[ic].y;
        roi_c.width = (faces[ic].width);
        roi_c.height = (faces[ic].height);

        ac = roi_c.width * roi_c.height; // Get the area of current element (detected face)

        roi_b.x = faces[ib].x;
        roi_b.y = faces[ib].y;
        roi_b.width = (faces[ib].width);
        roi_b.height = (faces[ib].height);

        ab = roi_b.width * roi_b.height; // Get the area of biggest element, at beginning it is same as "current" element

        if (ac > ab)
        {
            ib = ic;
            roi_b.x = faces[ib].x;
            roi_b.y = faces[ib].y;
            roi_b.width = (faces[ib].width);
            roi_b.height = (faces[ib].height);
        }

        crop = frame(roi_b);
        resize(crop, res, Size(92, 112), 0, 0, INTER_LINEAR); // This will be needed later while saving images        

        cvtColor(crop, gray, CV_BGR2GRAY); // Convert cropped image to Grayscale

        // Form a filename
        filename = "";
        stringstream ssfn;
        ssfn << filenumber << ".pgm";
        filename = ssfn.str();
        filenumber++;

        imwrite(filename, gray);

        Point pt1(faces[ic].x, faces[ic].y); // Display detected faces on main window - live stream from camera
        Point pt2((faces[ic].x + faces[ic].height), (faces[ic].y + faces[ic].width));
        rectangle(frame, pt1, pt2, Scalar(0, 255, 0), 2, 8, 0);
    }

// Show image
    sstm << "Crop area size: " << roi_b.width << "x" << roi_b.height << " Filename: " << filename;
    text = sstm.str();

    putText(frame, text, cvPoint(30, 30), FONT_HERSHEY_COMPLEX_SMALL, 0.8, cvScalar(0, 0, 255), 1, CV_AA);
    imshow("original", frame);

    if (!crop.empty())
    {
        imshow("detected", crop);
    }
    else
        destroyWindow("detected");
}

Answer 1

您在“调整图像大小”部分弄错了。 cv::resize 定义为

void resize(InputArray src, OutputArray dst, Size dsize, double fx=0, double fy=0, int interpolation=INTER_LINEAR )

因此在您的代码中，当您调用

resize(crop, res, Size(92, 112), 0, 0, INTER_LINEAR);

调整大小后的图像存储在“res”中，而不是“crop”中。

裁剪部分的正确代码是:

crop = frame(roi_b);
resize(crop, res, Size(92, 112), 0, 0, INTER_LINEAR); // This will be needed later while saving images

cvtColor(res, gray, CV_BGR2GRAY); // Convert cropped image to Grayscale

'gray' 是调整大小的裁剪图像的灰度结果。