old_contents: 
  var fs = require('fs'),
      PNG = require('pngjs').PNG;
  
  
  fs.readdir(__dirname + '/img/', function(err, files) {
      if (err) throw err;
  
      files.forEach(function(file) {
  
          if (!file.match(/\.png$/i))
              return;
  
          fs.createReadStream(__dirname + '/img/' + file)
              .pipe(new PNG())
              .on('parsed', function() {
  
                  if (this.gamma) {
                      for (var y = 0; y < this.height; y++) {
                          for (var x = 0; x < this.width; x++) {
                              var idx = (this.width * y + x) << 2;
  
                              for (var i = 0; i < 3; i++) {
                                  var sample = this.data[idx + i] / 255;
                                  sample = Math.pow(sample, 1 / 2.2 / this.gamma);
                                  this.data[idx + i] = Math.round(sample * 255);
                              }
                          }
                      }
                  }
  
                  this.pack()
                      .pipe(fs.createWriteStream(__dirname + '/out/' + file));
  
              });
  
      });
  });
  
new_contents: 
  var fs = require('fs'),
      PNG = require('pngjs').PNG;
  
  
  fs.readdir(__dirname + '/img/', function(err, files) {
      if (err) throw err;
  
      files.forEach(function(file) {
  
          if (!file.match(/\.png$/i))
              return;
  
          fs.createReadStream(__dirname + '/img/' + file)
              .pipe(new PNG())
              .on('parsed', function() {
  
                  if (this.gamma) {
                      for (var y = 0; y < this.height; y++) {
                          for (var x = 0; x < this.width; x++) {
                              var idx = (this.width * y + x) << 2;
  
                              for (var i = 0; i < 3; i++) {
                                  var sample = this.data[idx + i] / 255;
                                  sample = Math.pow(sample, 1 / 2.2 / this.gamma);
                                  this.data[idx + i] = Math.round(sample * 255);
                              }
                          }
                      }
                  }
  console.log(file);
                  this.pack()
                      .pipe(fs.createWriteStream(__dirname + '/out/' + file));
  
              });
  
      });
  });
  
subject: fix sample png