OpenCV && C++ 03

Code

/*
作者：郑大峰
时间：2019年09月20日
环境：OpenCV 4.1.1 + VS2017
内容：Save an Image to a File
*/

#include "pch.h"
#include <iostream>
#include <opencv2/opencv.hpp>

using namespace std;
using namespace cv;

int main()
{
	Mat image = imread("claudia.png");

	if (image.empty())
	{
		cout << "Could not open or find the image" << endl;
		cin.get();
		return -1;
	}

	/*
	Make changes to the image as necessary
	e.g.
	 1. Change brightness/contrast of the image
	 2. Smooth/Blur image
	 3. Crop the image
	 4. Rotate the image
	 5. Draw shapes on the image
	*/

	//bool isSuccess = imwrite("claudia_changed.jpg", image); //write the image to a file as JPEG 
	bool isSuccess = imwrite("claudia_changed.png", image); //write the image to a file as PNG
	if (isSuccess == false)
	{
		cout << "Failed to save the image" << endl;
		cin.get();
		return -1;
	}

	cout << "Image is succusfully saved to a file" << endl;
	cin.get();

	return 0;
}

Result

Explanation

bool imwrite( const String& filename, InputArray img, const std::vector& params = std::vector())

@brief Saves an image to a specified file.

The function imwrite saves the image to the specified file. The image format is chosen based on the filename extension (see cv::imread for the list of extensions). In general, only 8-bit single-channel or 3-channel (with 'BGR' channel order) images can be saved using this function, with these exceptions:

• 16-bit unsigned (CV_16U) images can be saved in the case of PNG, JPEG 2000, and TIFF formats
• 32-bit float (CV_32F) images can be saved in PFM, TIFF, OpenEXR, and Radiance HDR formats; 3-channel (CV_32FC3) TIFF images will be saved using the LogLuv high dynamic range encoding (4 bytes per pixel)
• PNG images with an alpha channel can be saved using this function. To do this, create 8-bit (or 16-bit) 4-channel image BGRA, where the alpha channel goes last. Fully transparent pixels should have alpha set to 0, fully opaque pixels should have alpha set to 255/65535 (see the code sample below).

If the format, depth or channel order is different, use Mat::convertTo and cv::cvtColor to convert it before saving. Or, use the universal FileStorage I/O functions to save the image to XML or YAML format.

The sample below shows how to create a BGRA image and save it to a PNG file. It also demonstrates how to set custom compression parameters:
@include snippets/imgcodecs_imwrite.cpp
@param filename Name of the file.
@param img Image to be saved.
@param params Format-specific parameters encoded as pairs (paramId_1, paramValue_1, paramId_2, paramValue_2, ... .) see cv::ImwriteFlags