Loads a JPEG image into memory, storing the width and height as properties of a JPEG object using Node.JS

JPGE Image dimensions

var fs = require('fs');


function JPEG(filename) {
	var image = this;
	image.blob = null;

	if (filename) {
		image = JPEG.loadFromFile(filename);
	}
	
	return image;
}

JPEG.prototype = {
	init: function () {
		try {
			var dimensions = getDimensions(this.blob);
			this.width = dimensions.width;
			this.height = dimensions.height;
		} catch (e) {
			console.log(e);
			process.exit(0);
		}
	},
	width: 0,
	height: 0,
	blob: null
};

JPEG.loadFromFile = function (filename) {
	var image = new JPEG();
	image.blob = fs.readFileSync(filename);
	image.init();

	return image;
};

JPEG.loadFromBlob = function (blob) {
	var image = new JPEG();
	image.blob = blob;
	image.init();

	return image;
};

function getDimensions(blob) {
	if (blob[0] != 0xFF || blob[1] != 0xD8) {
		throw 'Image is not valid: No JPG header found';
		return null;
	}

	var offset = 2;
	var blob_size = blob.length;

	while (offset != blob_size - 1) {
		var c = blob[offset++], skip = 0;

		if (offset == blob_size - 1 || c != 0xFF) {
			throw 'Image is not valid: JPG marker error';
			return null;
		}

		c = blob[offset++];
		if (c == 0xC0) { // frame
			offset += 3; // length and BPP

			return {
				width: blob[offset++] << 8 | blob[offset++],
				height: blob[offset++] << 8 | blob[offset++]
			};
		} else if (c == 0xC2) { // frame
			offset += 3; // length and BPP

			return {
				width: blob[offset++] << 8 | blob[offset++],
				height: blob[offset++] << 8 | blob[offset++]
			};
		} else if (c == 0xD9) {
			throw 'Image is not valid: End of JPG found but no frame data';
		} else if (c == 0xDD) {
			skip = 2;
		} else if (c >= 0xD0 && c <= 0xD7) {
			skip = 0;
		} else {
			skip = blob[offset++] << 8 | blob[offset++];
			skip -= 2;
		}

		offset += skip;
	}
}

exports.JPEG = JPEG;