Creating a PNG from uncompressed raw PNG data

I am using this Android Screenshot Library to capture screenshots. I want to show this screenshot in web browser.

I have written a small socket app on PC which connects to Android phone and encode the captured screenshot to base64.

String base64 = Base64.getEncoder().encodeToString(bytes);

This base64 is being sent to web page over websocket. Below is my html/JS code which should draw the image on canvas. I have stored the base64 image data in a text file for test purpose.

<div style="background: aqua; width: 500px; height: 660px;">

    <canvas style="width: 480px; height: 640px;" id="sim">

<script type="text/javascript">
    var ctx;
    var width = 480;
    var height = 640;

    (function start() {
        ctx = document.getElementById("sim").getContext("2d");

    function loadImage(data) {

        var image = new Image();
        image.onload = function() {
            //this part never executes
            ctx.drawImage(image, 0, 0);
            console.log("images loaded!");

        image.src = "data:image/png;base64," + data;

    function loadFromFile() {
        //please get data from ****
        var file = "imagefile.txt";

        var rawFile = new XMLHttpRequest();"GET", file, true);

        rawFile.onreadystatechange = function() {
            if (rawFile.readyState === 4) {
                if (rawFile.status === 200 || rawFile.status == 0) {
                    var data = rawFile.responseText;
                    console.log("data loaded: " + data.length);


For convenience, here is the JsFiddle of same code.

Please point to right algorithm as how to generate the PNG from the raw uncompressed data. code sample would be great 😉


Source: c#

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