Converting a hex string of a raw image to a bitmap image in JavaScript

Introduction:

I am reading image data of fingerprints from smart card and as you know this data save as raw image in smart card. I am developing a client side program which only use java script to read image from scanner of a card reader and show that in the client page.

Now my question:

How can I convert hex string of my raw data to a hex string which accomplished with appropriate header of bitmap image? Note that I have width and height of my image.

Tried methods:

I have been developed this program in java by get buffered image from raw data. Also, I could convert a hex string of a bit map image to base64 by Hex2Base64 and then I could show base64 string in an image tag by base64AsImage. However these functions work well if and only if the hex contains header, while our data is raw.

My code (that only works for Hex String which contains header):

<!DOCTYPE html>
<html>
<head lang="en">
    <meta charset="UTF-8">
    <title></title>

    <script>
        if (!window.atob) {
            var tableStr = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
            var table = tableStr.split("");

            window.atob = function (base64) {
                if (/(=[^=]+|={3,})$/.test(base64)) throw new Error("String contains an invalid character");
                base64 = base64.replace(/=/g, "");
                var n = base64.length & 3;
                if (n === 1) throw new Error("String contains an invalid character");
                for (var i = 0, j = 0, len = base64.length / 4, bin = []; i < len; ++i) {
                    var a = tableStr.indexOf(base64[j++] || "A"), b = tableStr.indexOf(base64[j++] || "A");
                    var c = tableStr.indexOf(base64[j++] || "A"), d = tableStr.indexOf(base64[j++] || "A");
                    if ((a | b | c | d) < 0) throw new Error("String contains an invalid character");
                    bin[bin.length] = ((a << 2) | (b >> 4)) & 255;
                    bin[bin.length] = ((b << 4) | (c >> 2)) & 255;
                    bin[bin.length] = ((c << 6) | d) & 255;
                };
                return String.fromCharCode.apply(null, bin).substr(0, bin.length + n - 4);
            };

            window.btoa = function (bin) {
                for (var i = 0, j = 0, len = bin.length / 3, base64 = []; i < len; ++i) {
                    var a = bin.charCodeAt(j++), b = bin.charCodeAt(j++), c = bin.charCodeAt(j++);
                    if ((a | b | c) > 255) throw new Error("String contains an invalid character");
                    base64[base64.length] = table[a >> 2] + table[((a << 4) & 63) | (b >> 4)] +
                    (isNaN(b) ? "=" : table[((b << 2) & 63) | (c >> 6)]) +
                    (isNaN(b + c) ? "=" : table[c & 63]);
                }
                return base64.join("");
            };

        }

        function hexToBase64(str) {
            return btoa(String.fromCharCode.apply(null,
                            str.replace(/\r|\n/g, "").replace(/([\da-fA-F]{2}) ?/g, "0x$1 ").replace(/ +$/, "").split(" "))
            );
        }

        function base64ToHex(str) {
            for (var i = 0, bin = atob(str.replace(/[ \r\n]+$/, "")), hex = []; i < bin.length; ++i) {
                var tmp = bin.charCodeAt(i).toString(16);
                if (tmp.length === 1) tmp = "0" + tmp;
                hex[hex.length] = tmp;
            }
            return hex.join(" ");
        }
        function doConvert() {
            var myHex =  document.getElementById('myText').value;
            var myBase64 = hexToBase64(myHex);
            document.getElementById('myImage').src = "data:image/bmp;base64," +  myBase64;
        }
    </script>



</head>
<body>
<div>
    <p>
        Enter Raw Hex:
        <br>
        <textarea rows="4" cols="50" id="myText">Enter Raw Hex String here ...</textarea>
        <br>
        <button id="myButton" onclick="doConvert()"> Click me </button>
        <br>
        <img id="myImage" alt="img1"/>
    </p>
</div>
</body>
</html>

a part of code which solve the problem in java:

private static BufferedImage byte2Buffered(byte[] rawData, int width, int height){
    BufferedImage image = new BufferedImage(width,height,BufferedImage.TYPE_BYTE_GRAY);
    byte[] array = ((DataBufferByte)image.getRaster().getDataBuffer()).getData();
    System.arraycopy(rawData, 0, array, 0, rawData.length);
    return image;
}

Notice that, as there is not BufferedImage type in JavaScript, we could not equivalent this approach in JavaScript.

Answers:

Answer

In your window.atob method, you are building a string from an array of 8-bit integers already (that's what bin[length] is creating.) Just return that array instead of the string.

Then, if you have to support older browsers, you will need to write each pixel to the canvas individually. But if you can target modern browsers, just build a Uint8ClampedArray, put that into an ImageData object, and putImageData() into the canvas.

Below is some working sample code. I'm populating a dummy array with random bytes (data), but you would use the byte array returned from atob.

var canvas = document.querySelector('canvas'),
    ctx = canvas.getContext('2d'),
  width = canvas.width,
  height = canvas.height,
  pixelLength = width * height,
  data,
  imageData;

// You can use any kind of array, including a
// Uint8ClampedArray, since it is just going to be
// crammed into a clamped array anyway. I'm using a
// Uint8Array just as an example.
data = new Uint8Array(pixelLength);

// Create an array of random data
data = data.map(function (btye) { return Math.floor(Math.random() * 256); });

// The source data is 8-bit grayscale, but it needs 
// to be 32-bit RGBA in a Uint8ClampedArray. The
// structure is simple. For every byte of the gray-
// scale array, write out three copies of that byte 
// and then `256` as 100% opaque.
data = data.reduce(function (carry, current, index) {
    var baseIndex = index * 4;

  carry[baseIndex] = current;
    carry[baseIndex + 1] = current;
    carry[baseIndex + 2] = current;
    carry[baseIndex + 3] = 256;

return carry;
}, new Uint8ClampedArray(pixelLength * 4));

// The Uint8ClampedArray can now be used to build the image
imageData = new ImageData(data, width, height);
ctx.putImageData(imageData, 0, 0);

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