Main.java

import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.nio.ByteBuffer;
import java.nio.ByteOrder;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.util.Arrays;


public class Main {

    public static void main(String[] args) {


        File f = new File("/home/paolorotolo/anna2.bmp");
        Path path = Paths.get(f.toURI());

        byte[] bytes = null;

        try {
            bytes = Files.readAllBytes(path);
        } catch (IOException e) {
            e.printStackTrace();
        }

        ByteBuffer buffer = null;

        byte[] widthBytes = Arrays.copyOfRange(bytes, 18, 22);
        System.out.println(widthBytes.length);
        int width = buffer.wrap(widthBytes).order(ByteOrder.LITTLE_ENDIAN).getInt();
        System.out.println("Width is: " + width);

        byte[] heightBytes = Arrays.copyOfRange(bytes, 22, 26);
        int height = buffer.wrap(heightBytes).order(ByteOrder.LITTLE_ENDIAN).getInt();
        System.out.println("Height is " + height);
        System.out.println("Size is " + bytes.length);

        byte[] headerBytes = Arrays.copyOfRange(bytes, 0, 1078);

        byte[] imageByte = Arrays.copyOfRange(bytes, 1079, bytes.length);
        for (int i = 0; i < imageByte.length; i++) {
            int convertedValue = ((int) imageByte[i] & 0xFF);
            imageByte[i] = (byte) (255 - convertedValue);
        }

        try {
            FileOutputStream fos = new FileOutputStream("convertito.bpm");
            fos.write(headerBytes);
            fos.write(imageByte);
            fos.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}