Read and Write PNG in Binary

png.js

// PNG 格式定义
// http://dev.gameres.com/Program/Visual/Other/PNGFormat.htm

var fs = require('fs');

// 测试文件
var FILE_IN = 'in.png'
  , FILE_OUT = 'out.png';

var out = '';

// 标识符、区块
var SIGNATURE = '89504e470d0a1a0a'
  , SIGNATURE_POSITION = 0
  , IHDR = '49484452'
  , IHDR_POSITION = 0
  , IHDR_LENGTH = 0
  , IHDR_SEGMENT = ''
  , IDAT = '49444154'
  , IDAT_POSITION = 0
  , IDAT_LENGTH = 0
  , IDAT_SEGMENT = ''
  , IEND = '0000000049454e44ae426082'
  , IEND_POSITION = 0;

// 读文件
fs.readFile(FILE_IN, function (err, data) {
  if (err) throw err;

  var h = data.toString('hex');

  // 读取块
  SIGNATURE_POSITION = h.indexOf(SIGNATURE);

  IHDR_POSITION = h.indexOf(IHDR);
  IHDR_LENGTH = parseInt(h.substring(IHDR_POSITION - 8, IHDR_POSITION), 16);
  IHDR_SEGMENT = h.substring(IHDR_POSITION - 8, IHDR_POSITION + 8 + IHDR_LENGTH * 2 + 8);

  IDAT_POSITION = h.indexOf(IDAT);
  IDAT_LENGTH = parseInt(h.substring(IDAT_POSITION - 8, IDAT_POSITION), 16);
  IDAT_SEGMENT = h.substring(IDAT_POSITION - 8, IDAT_POSITION + 8 + IDAT_LENGTH * 2 + 8);

  IEND_POSITION = h.indexOf(IEND);

  // 生成块
  out += SIGNATURE;
  out += IHDR_SEGMENT;
  out += IDAT_SEGMENT;
  out += IEND;

  outBuffer = new Buffer(out, 'hex');

  // 写文件
  fs.writeFile(FILE_OUT, outBuffer, function (err) {
    if (err) throw err;
    console.log('OK');
  });
});