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              <div id="dropzone"> 
  <p class="canvasp">Suelte una imagen aquí<br>Drag your file here</p>
<p id="dataUri"></p>
              #dropzone {
  display: block;
  width: 300px;
  height: 300px;
  position: relative;
  margin: 50px auto 0;
  padding: 0;

canvas {
  border: 1px dashed;
  font-size: 2em;
  width: 300px;
  height: 300px;

p{word-wrap: break-word;text-align: center;}
p.canvasp {
  display: block;
  width: 300px;
  position: absolute;
  top: 118px;
  z-index: -1;

              var outputDataUri = document.querySelector("p#dataUri");
var url = "";

var canvas = document.querySelector("canvas");
var ctx = canvas.getContext("2d");
var cw = canvas.width = 300,
  cx = cw / 2;
var ch = canvas.height= 300,
  cy = ch / 2;

canvas.addEventListener("dragenter", dragenter, false);
canvas.addEventListener("dragover", dragover, false);
canvas.addEventListener("drop", drop, false);

function dragenter(e) {

function dragover(e) {

function drop(e) {

  var datos = e.dataTransfer;
  var archivos = datos.files;


function manejarArchivos(archivos) {
  for (var i = 0; i < archivos.length; i++) {
    var archivo = archivos[i];
    var esImagen = /^image\//;
    if (!esImagen.test(archivo.type)) {
    var img = new Image(); 
    img.src = window.URL.createObjectURL(archivo);
    img.onload = function() {   
    var w = img.width;
    var h = img.height;
    // centrar la imagen  
    ctx.drawImage(this, cx - w/2, cy - h/2, w, h);
    url = canvas.toDataURL();
    outputDataUri.innerHTML = "<img src='"+url+"' alt='data:URI' />";    window.URL.revokeObjectURL(this.src);  

function negativo(ctx,cw,ch){
	//Devuelve un objeto imgData con los datos de todos los píxeles de la imagen
    var imgData = ctx.getImageData(0, 0, cw, ch);
    var pixels = imgData.data;
	// recorre uno a uno los pixeles de la imagen y cambia el color por el complementario
    for (var i = 0; i < pixels.length; i += 4) {
      pixels[i] = 255 - pixels[i]; // rojo
      pixels[i + 1] = 255 - pixels[i + 1]; // verde
      pixels[i + 2] = 255 - pixels[i + 2]; // azul
	// pone la imagen modificada en el canvas
     ctx.putImageData(imgData, 0, 0, 0, 0, cw, ch)
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