title: Reading and writing .PPM image in java?
body: <p>I have to read a ppm image in java and then convert the image to negative. Then PPM image has a magic number "P6" and then a # Comment char, and then height and width. and finally has 255 character, that is followed by data.
  i want to read header and verify if it is P3 or P6.
  and then read image dimension and then using java convert the data to negative of the image,
  Please suggest me the best way to do it</p>