gistfile1.js

/*
Expanding color pixels on the current (and only loaded image)
*/
var doc = app.documents[0];

doc.colorSamplers.removeAll(); // otherwise it will create an error if there is already a colorSampler on this point

var offset = 4;
for (var w=0; w < doc.width; w+=offset) {
  for (var h=0; h < doc.height; h+=offset) {
    try {
      doc.colorSamplers.removeAll();
      var cSampler = doc.colorSamplers.add([w+1,h+1]);
      var color = cSampler.color;
      doc.selection.select([
        [w,h],
        [w+offset,h],
        [w+offset, h+offset],
        [w,h+offset]
      ]);
      doc.selection.fill(color);
    } catch (e){}
  };
};