Convert all images in a folder into grey scale image

greyscaleconvert.java

import java.awt.Color;
import java.awt.image.BufferedImage;
import java.io.BufferedWriter;
import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.OutputStreamWriter;
import java.io.RandomAccessFile;
import java.io.Writer;
import java.nio.channels.FileChannel;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.util.stream.Stream;

import javax.imageio.ImageIO;

public class TransformFiles {
	
	public static void main(String[] args) throws IOException {
		
		final File folder= new File("C:\\Users\\User\\Desktop\\Road and Cars\\Road_negatives");
		for (final File fileEntry : folder.listFiles()) {
		       
			 BufferedImage img = null;
			   

			    //read image
			    try{
			     
			      img = ImageIO.read(fileEntry);
			    }catch(IOException e){
			      System.out.println(e);
			    }

			    //get image width and height
			    int width = img.getWidth();
			    int height = img.getHeight();

			    //convert to grayscale
			    for(int y = 0; y < height; y++){
			      for(int x = 0; x < width; x++){
			        int p = img.getRGB(x,y);

			        int a = (p>>24)&0xff;
			        int r = (p>>16)&0xff;
			        int g = (p>>8)&0xff;
			        int b = p&0xff;

			        //calculate average
			        int avg = (r+g+b)/3;

			        //replace RGB value with avg
			        p = (a<<24) | (avg<<16) | (avg<<8) | avg;

			        img.setRGB(x, y, p);
			      }
			    }

			    //write image
			    try{
			      
			      ImageIO.write(img, "jpg",new File("C:\\Users\\User\\Desktop\\Road and Cars\\negative\\"+fileEntry.getName()));
			    }catch(IOException e){
			      System.out.println(e);
			    }
		 }
			
	
	}
}


/*
 *   BufferedImage inputFile = null;
		        try {
		            inputFile = ImageIO.read(fileEntry);
		        } catch (IOException e) {
		            e.printStackTrace();
		        }

		        for (int x = 0; x < inputFile.getWidth(); x++) {
		            for (int y = 0; y < inputFile.getHeight(); y++) {
		                int rgba = inputFile.getRGB(x, y);
		                Color col = new Color(rgba, true);
		                col = new Color(255 - col.getRed(),
		                                255 - col.getGreen(),
		                                255 - col.getBlue());
		                inputFile.setRGB(x, y, col.getRGB());
		            }
		        }

		        try {
		            File outputFile = new File("C:\\Users\\User\\Desktop\\Road and Cars\\negative\\"+fileEntry.getName());
		            ImageIO.write(inputFile, "jpg", outputFile);
		        } catch (IOException e) {
		            e.printStackTrace();
		        }
		        */