시각적인 것이 왜 중요할까요?

var image;

function upload() {
  var canvas=document.getElementById("can");
  var fileinput=document.getElementById("finput");
  image=new SimpleImage(fileinput);
  image.drawTo(canvas);
}

function makeGrey() {
    for (var pixel of image.values()){
        var avg =(pixel.getRed()+pixel.getGreen()+pixel.getBlue())/3;
        pixel.setRed(avg);
        pixel.setGreen(avg);
        pixel.setBlue(avg);
    }
  var canvas=document.getElementById("can2");
  image.drawTo(canvas);
}

function docolor() {
  var dd1=document.getElementById("d1");
  var colorinput=document.getElementById("clr");
  var color = colorinput.value;
  dd1.style.backgroundColor=color;
}

function dosquare() {
  var dd1=document.getElementById("d1");
  var sizeinput=document.getElementById("slr");
  var size = sizeinput.value;
  var ctx=dd1.getContext("2d");
  ctx.clearRect(0,0, dd1.width, dd1.height);
  ctx.fillStyle="#8B0000";
  ctx.fillRect(10,10,size,size);
  ctx.fillRect(parseInt(size)+20,10,size,size);
  //ctx.fillRect(size*3,10,size,size);
}