A program that converts the supplied image to grayscale using the lightness algorithm. Made quickly for /r/dailyprogrammer challenge 179

grayscaler.java

package javagrayscaler;

import java.awt.image.BufferedImage;
import java.io.File;
import java.io.IOException;
import javax.imageio.ImageIO;

public class JavaGrayscaler 
{
    static String filePath = "";
    
    static int lightness(int r, int g, int b)
    {
        int max = Math.max(r, Math.max(g,b));
        int min = Math.min(r, Math.min(g,b));
        return (max+min)/2;
    }
    
    public static BufferedImage imageToGrayscale(BufferedImage image)
    {
        BufferedImage img = new BufferedImage(image.getWidth(), image.getHeight(), BufferedImage.TYPE_BYTE_GRAY);
        for (int y = 0; y < image.getHeight(); y++) 
        {
            for (int x = 0; x < image.getWidth(); x++) 
            {
                int  clr   = image.getRGB(x, y); 
                int  r   = (clr & 0x00ff0000) >> 16;
                int  g = (clr & 0x0000ff00) >> 8;
                int  b  =  clr & 0x000000ff;
                int grayLevel = lightness(r,g,b);
                int gray = (grayLevel << 16) + (grayLevel << 8) + grayLevel; 
                img.setRGB(x, y, gray);
            }
        }
        return img;
    }
    
    public static void main(String[] args) 
    {
        
        if(args.length != 1)
        {
            System.out.println("No file supplied as argument, terminating");
            System.exit(0);
        }
        else
        {
            filePath = args[0];
            File f = new File(filePath);
            try 
            {
                System.out.println("Starting conversion...");
                BufferedImage image = ImageIO.read(f);
                BufferedImage converted = imageToGrayscale(image);
                String ext = f.getPath().substring(f.getPath().lastIndexOf("."));
                ImageIO.write(converted, "png", new File("gray" + ext));
                System.out.println("Converted");
            }
            catch(IOException e)
            {
                System.out.println(e.getMessage());
            }
            
        }
        
    }

}