trying to convert pixels to little endian byte array for thermal printing

image_to_byte_array.pde

import java.nio.*;

byte[] imageBytes;
PImage img;

PrintWriter output;

void setup() {

  size(500, 500);

  img = loadImage("bmptest.bmp");
  imageBytes = loadBytes("bmptest.bmp");
  background(0);

  fill(255);
  stroke(255);
  text("byte length: " + imageBytes.length, 10, img.height+20);
  text("pixel count: " + img.pixels.length, 10, img.height+35);

  text("pixels/8: " + img.pixels.length / 8, 10, img.height+50);
  text("w: "+ img.width + " h: " +img.height, 10, img.height+65);

  noLoop();

  output = createWriter("testimg.cpp");
  output.println("//------------------------------------------------------------------------------");
  output.println("// generated by Greg Borenstein's probably buggy Processing Sketch");
  output.println();
  output.println("//------------------------------------------------------------------------------");
  output.println();
  output.println("const unsigned char fakethesis [] = {");
}

void draw() {
  img.loadPixels();

  image(img, 0, 0);

  int bCounter = 0;
  String currentByte = "";
  int byteCount = 0;


  for (int i = 3; i < img.pixels.length; i++) {

    int pixelValue = int(map(brightness(img.pixels[i]), 0, 255, 1, 0));
    currentByte += pixelValue;
    bCounter++;
    if (bCounter > 7) {
      currentByte = reverseString(currentByte);
      
      String s = String.format("0x%02X", Integer.parseInt(currentByte, 2));

      output.print(s);

      bCounter = 0;
      currentByte = "";
      byteCount++;

      if (i < img.pixels.length - 8) {
        output.print(", ");
      }
    }

    if ((i % 128) == 0 ) {
      output.println();
    }
  }

  output.println("};");

  output.flush(); // Write the remaining data
  output.close(); // Finish the file

}

String reverseString(String input){
  String output = "";

  for(int i = 0; i<input.length(); i++){
    output += input.charAt(input.length() - (i+1));
  }
   
  return output;
}


int reverseEndianness(int x) {  
  ByteBuffer bbuf = ByteBuffer.allocate(8);  
  bbuf.order(ByteOrder.BIG_ENDIAN);  
  bbuf.putInt(x);  
  bbuf.order(ByteOrder.LITTLE_ENDIAN);  
  return bbuf.getInt(0);
}