java - Converting image to byte array, then to int array, then to byte array for image output -

i'm trying implement dct on image, , far have been able read image, grayscale it, turn byte array , output byte array image. works fine. however, in order work on image need convert byte array int array , again, , problem comes in.

this first part reads image , converts image grayscale.

bufferedimage image = imageio.read(new file("c:\\users\\a00226084\\desktop\\image.jpg"));  int width = image.getwidth(); int height = image.getheight();  for(int i=0; i<height; i++){      for(int j=0; j<width; j++){          color c = new color(image.getrgb(j, i));         int red = (int)(c.getred() * 0.299);         int green = (int)(c.getgreen() * 0.587);         int blue = (int)(c.getblue() *0.114);         color newcolor = new color(red+green+blue,          red+green+blue,red+green+blue);          image.setrgb(j,i,newcolor.getrgb());     } } 

this part converts image byte array.

bytearrayoutputstream baos = new bytearrayoutputstream(); imageio.write(image, "jpg", baos); byte[] pixels = baos.tobytearray(); 

this part converts byte array int array. have manually done wrapping because nothing else worked.

for(int = 0; < pixels.length; ++){     if(pixels[i] < 0){         byteconverted[i] = 127 + (128 - (pixels[i] * -1));     }else{         byteconverted[i] = pixels[i];      } } 

this part converts int array byte array, somewhere between byte > int , int > byte conversions goes wrong. have output both before , after byte array file , identical, don't know why 'image == null' instead of image.

for(int = 0; < pixels.length; ++){     if(byteconverted[i] > 127){         pixels[i] = (byte) ( -128 + (byteconverted[i] - 127));     }else{         pixels[i] = (byte) byteconverted[i];     } } write2("final byte array.txt", pixels);  bytearrayinputstream bais = new bytearrayinputstream(pixels);  try {     bufferedimage img = imageio.read(bais);     system.out.println("image out");     system.out.println(pixels.length);     imageio.write(img, "jpg", new file("c:\\users\\a00226084\\desktop\\newimage.jpg")); } catch (ioexception e) {     e.printstacktrace(); }