Resize Image using OpenCV

Image resizing reduces the number of pixels in an image. It can be useful when want to decrease image processing time or reduce the time of training of a neural network.

OpenCV provides the resize function which resizes the image down to or up by the specified width and height.

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import cv2

width = 320
height = 240

img = cv2.imread('test.jpg')
resizedImg = cv2.resize(img, (width, height))

cv2.imshow('Original image', img)
cv2.imshow('Resized image', resizedImg)
cv2.waitKey(0)
cv2.destroyAllWindows()

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#include <opencv2/opencv.hpp>

using namespace cv;

int main()
{
    int width = 320;
    int height = 240;

    Mat img = imread("test.jpg");
    Mat resizedImg;
    resize(img, resizedImg, Size(width, height));

    imshow("Original image", img);
    imshow("Grayscale image", resizedImg);
    waitKey(0);
    destroyAllWindows();

    return 0;
}

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

using namespace cv;

int main()
{
    int width = 320;
    int height = 240;

    Mat img = imread("test.jpg");
    cuda::GpuMat gpuImg(img);
    cuda::resize(gpuImg, gpuImg, Size(width, height));
    Mat resizedImg(gpuImg);

    imshow("Original image", img);
    imshow("Grayscale image", resizedImg);
    waitKey(0);
    destroyAllWindows();

    return 0;
}

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package app;

import org.opencv.core.*;
import org.opencv.highgui.HighGui;
import org.opencv.imgcodecs.Imgcodecs;
import org.opencv.imgproc.Imgproc;

public class Main
{
    static { System.loadLibrary(Core.NATIVE_LIBRARY_NAME); }

    public static void main(String[] args)
    {
        int width = 320;
        int height = 240;

        Mat img = Imgcodecs.imread("test.jpg");
        Mat resizedImg = new Mat();
        Imgproc.resize(img, resizedImg, new Size(width, height));

        HighGui.imshow("Original image", img);
        HighGui.imshow("Resized image", resizedImg);
        HighGui.waitKey(0);
        HighGui.destroyAllWindows();

        System.exit(0);
    }
}

Result: