copyMakeBorder

Usage

Adds a border around an image. It is used for data augmentation, avoiding edge effects, or adding decorative borders to images.

Interface

void copyMakeBorder(InputArray src, OutputArray dst, int top, int bottom, int left, int right, int borderType, const Scalar& value = Scalar());

Parameters

Parameter	Description	Value Range	Input/Output
src	Input image.	Not null	Input
dst	Output image.	Mat class	Input
top	Border size in top direction.	(0, inf)	Input
bottom	Border size in bottom direction.	(0, inf)	Input
left	Border size in left direction.	(0, inf)	Input
right	Border size in right direction.	(0, inf)	Input
borderType	Border type.	BORDER_CONSTANT BORDER_REPLICATE BORDER_REFLECT BORDER_WRAP, etc.	Input
value	Constant value used to fill the border (valid only for a constant border).	(0, inf)	Input

Example

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

using namespace cv;

int main() {
    // Read the image.
    Mat src = imread("input.jpg");
    if (src.empty()) {
        std::cerr << "Failed to load the image!" << std::endl;
        return -1;
    }

    // Set border sizes.
    int top = 10, bottom = 10, left = 20, right = 20;

    // Image expansion
    Mat dst;
    copyMakeBorder(src, dst, top, bottom, left, right, BORDER_CONSTANT, Scalar(255, 255, 255));

    // Display the result.
    imshow("Original image", src);
    imshow("Image after expansion", dst);
    waitKey(0);

    return 0;
}

Parent topic: Interface Definition