It's alive 2

//image thing
var pasteimagehere=document.createElement("div");
pasteimagehere.style.width="3.25rem";
pasteimagehere.id="pasteimagehere";
pasteimagehere.setAttribute("contenteditable","");
document.querySelector("#sendpane").appendChild(pasteimagehere);

//get image from input
function checkInput(){
    var thing=document.getElementById("pasteimagehere").childNodes[0];
    if (thing){
        if (thing.tagName=="IMG") {
            var pastedImage=new Image();
            pastedImage.crossOrigin="Anonymous";
            pastedImage.onload=function(){
                putimage(pastedImage);
            };
            pastedImage.src=thing.src;
        }
    }
    document.getElementById("pasteimagehere").innerHTML="";
}

var imgInt=setInterval(function(){checkInput();},1000);//THE ONLY SOLUTION

function putimage(img){
    var palette=[];
    for(var i=0;i<4;i++)
        palette.push(fillStyleToRgb(document.querySelectorAll("#chatdraw button-area button.colorChange")[i].style.color));
    var canvas=document.querySelector("#chatdraw canvas");
    var c=canvas.getContext("2d");
    var scale=Math.min(canvas.width/img.width,canvas.height/img.height);
    c.drawImage(img,0,0,img.width,img.height,0,0,img.width*scale,img.height*scale);
    var data=c.getImageData(0,0,canvas.width,canvas.height);
    for(var x=0;x<data.data.length;x+=4){
        //get closeset color
        var low=null;
        var lowindex=null;
        for(var i=0;i<palette.length;i++){
            var ur=data.data[x]+palette[i][0];
            var cr=-data.data[x]+palette[i][0];
            var cg=-data.data[x+1]+palette[i][1];
            var cb=-data.data[x+2]+palette[i][2];
            var a=(2+ur/512)*cr*cr+4*cg*cg+(2+(510-ur)/512)*cb*cb;
            if(low===null||a<low){low=a;lowindex=i;}
        }
        //dithering
        var errr=(data.data[x  ]-palette[lowindex][0]);
        var errg=(data.data[x+1]-palette[lowindex][1]);
        var errb=(data.data[x+2]-palette[lowindex][2]);
        addRGB(x+4  ,5/16);
        addRGB(x+796,2/16);
        addRGB(x+800,5/16);
        addRGB(x+804,3/16);
        data.data[x  ]=palette[lowindex][0];
        data.data[x+1]=palette[lowindex][1];
        data.data[x+2]=palette[lowindex][2];

    }
    c.putImageData(data,0,0);

    function addRGB(index,amount) {
        if (index<data.data.length) {
            data.data[index  ]+=errr*amount;
            data.data[index+1]+=errg*amount;
            data.data[index+2]+=errb*amount;
        }
    }

    function getButtonColors() {
        var colors = [];
        for(var i = 0; i < 4; i++)
            colors.push(fillStyleToRgb(document.querySelectorAll("#chatdraw button-area button.colorChange")[i].style.color));
        return colors;
    }
}

var filebrowse=document.createElement("input");
filebrowse.type="file";
filebrowse.id="imageupload";
filebrowse.onchange=function(){loadimg();};
document.querySelector("#sidepane").appendChild(filebrowse);

function loadimg(){
    var reader=new FileReader();
    var z=new Image();
    reader.readAsDataURL(document.getElementById("imageupload").files[0]);
    reader.onload=function(){
        z.onload=function(){
            putimage(z);
        };
        z.src=reader.result;
    };
}