function Sprite(url, success){
    this.dataUrl = url || "";
    this.img = document.createElement("IMG");
    this.img.src = this.dataUrl;
    this.img.onload = success;
}

let pic = document.createElement('IMG');
pic.onload = function() {
    cvs.width = pic.width;
    cvs.height = pic.height;
    c.drawImage(pic, 0, 0);
    removeColor(c, [125, 25, 125], pic.width, pic.height);
    let ur = cvs.toDataURL();
    a[file.name] = new Sprite(ur, stepLoad);
}
pic.src = file.toURL();

let removeColor = function(ctx, rgb, w, h) {
    var imageData = ctx.getImageData(0, 0, w, h);

    // examine every pixel,
    // change any old rgb to the new-rgb
    for (var i = 0; i < imageData.data.length; i += 4) {
      // is this pixel the old rgb?
      if (imageData.data[i] == rgb[0] &&
        imageData.data[i + 1] == rgb[1] &&
        imageData.data[i + 2] == rgb[2]
      ) {
        // change to your new rgb
        imageData.data[i] = 0;
        imageData.data[i + 1] = 0;
        imageData.data[i + 2] = 0;
        imageData.data[i + 3] = 0;
      }
    }
    // put the altered data back on the canvas
    ctx.putImageData(imageData, 0, 0);
}