opencv-004-图像像素读写操作

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知识点

  1. C++中的像素遍历与访问
    • 数组遍历
    • 指针方式遍历
  2. Python中的像素遍历与访问
    • 数组遍历

代码（c++,python）

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#include <opencv2/opencv.hpp>
#include <iostream>

using namespace std;
using namespace cv;

/**
 * 读取图像，实现像素反转
 */
int main() {
    Mat src = imread("../images/liuyifei_1.png");
    Mat src_copy = src.clone();
    int height = src.rows;
    int width = src.cols;
    int ch = src.channels();
    imshow("input", src);

    // 直接读取图像像素
    for (int row = 0; row < height; ++row) {
        for (int col = 0; col < width; ++col) {
            if (ch == 3) {
                Vec3b bgr = src.at<Vec3b>(row, col);
                bgr[0] = 255 - bgr[0];
                bgr[1] = 255 - bgr[1];
                bgr[2] = 255 - bgr[2];
                src.at<Vec3b>(row, col) = bgr;
            } else if (ch == 1) {
                int gray = src.at<uchar>(row, col);
                src.at<uchar>(row, col) = 255 - gray;
            }
        }
    }
    imshow("output1", src);

    // 指针读取
    Mat result = Mat::zeros(src_copy.size(), src_copy.type());
    int blue = 0, green = 0, red = 0;
    int gray;
    for (int row = 0; row < height; ++row) {
        // curr_row为第row行的首地址，遍历时，前三个字节表示的是第一个像素的BGR值，
        // 注意BGR值顺序，接下来三个字节是第二个像素的值。
        uchar *curr_row = src_copy.ptr<uchar>(row);
        uchar *result_row = result.ptr<uchar>(row);
        for (int col = 0; col < width; ++col) {
            if (ch == 3) {
                blue = *curr_row++;
                green = *curr_row++;
                red = *curr_row++;

                *result_row++ = 255 - blue;
                *result_row++ = 255 - green;
                *result_row++ = 255 - red;
            } else if (ch == 1) {
                gray = *curr_row++;
                *result_row++ = gray;
            }
        }
    }

    imshow("output2", result);

    waitKey(0);
    return 0;
}
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import cv2 as cv

src = cv.imread("../images/liuyifei_1.png")
cv.namedWindow("input", cv.WINDOW_AUTOSIZE)
cv.imshow("input", src)
h, w, ch = src.shape
print("h , w, ch", h, w, ch)
for row in range(h):
    for col in range(w):
        b, g, r = src[row, col]
        b = 255 - b
        g = 255 - g
        r = 255 - r
        src[row, col] = [b, g, r]
cv.imshow("output", src)

cv.waitKey(0)
cv.destroyAllWindows()

结果

代码地址

github