Need Help Defining Variables

**Cyclone** · 02-08-2009, 05:06 AM

Hi,

I found this script here by Jacob Seidelin that uses ajax to retrieve image meta data.

I modified the script to only return a few values. Clicking on the link in the test page will show 3 values in an alert window.

My question is how do I isolate each one of those values into it's own variable? ex (x=0, y=1024, z= 683).

Also I would like to understnad how the code below works. I removed a lot of code from the orginal metadata script to try to simplify it in hopes I could understand it better but I'm not really sure how the script access and returns values from a file. For example, I'm trying to understand how the script finds the PixelXDimension value(0xA002).

Test Page
http://www.inspiredvisuals.com/test/test/test.html

Code:

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<html>
<head>
<script type="text/javascript" src="binaryajax.js"></script>
<script type="text/javascript" src="imageinfo.js"></script>

<script>


function GetExif()
{

	function callback()
	{	
		exif= files["image.jpg"]["exif"]
		var str = "";
		for (var a in exif) {str += exif[a] + "\r\n";}
		alert(str);
	}

	readFileData("image.jpg", callback);
	
}

</script>

</head>


<body>
<a href="#" onclick = "GetExif()">Get Image Dimensions Using EXIF Data</a>
</body>
</html>

Code:

/*
 * ImageInfo 0.1.2 - A JavaScript library for reading image metadata.
 * Copyright (c) 2008 Jacob Seidelin, jseidelin@nihilogic.dk, http://blog.nihilogic.dk/
 * MIT License [http://www.nihilogic.dk/licenses/mit-license.txt]
 */


var ImageInfo = {};

ImageInfo.useRange = true;
ImageInfo.range = 632;
var EXIF = {};
var iOffset = 2;

var files = [];

	function readFileData(url, callback) {
		BinaryAjax(
			url,
			function(http) {
				var tags = findEXIFinJPEG(http.binaryResponse);
				var mime = http.getResponseHeader("Content-Type");

				tags["mimeType"] = mime;
				tags["byteSize"] = http.fileSize;

				files[url] = tags;
				callback();
			},
			null,
			ImageInfo.useRange ? [0, ImageInfo.range] : null
		)
	}

function findEXIFinJPEG(oFile)
{
	var exif = {};

	EXIF.readFromBinaryFile = function(oFile)
	{
		while (iOffset < oFile.getLength())
		{	
			var iMarker = oFile.getByteAt(iOffset+1, true);
			if (iMarker == 225) {return readEXIFData(oFile)}
			else {iOffset += 2 + oFile.getShortAt(iOffset+2, true)}
		}
	}

	exif = EXIF.readFromBinaryFile(oFile);
	return {exif : exif}
}

function readTags(oFile, iDirStart, oStrings) 
{
	var oTags = {};
	
	for (var i=0;i<oFile.getShortAt(iDirStart);i++)
	{
		var strTag = oStrings[oFile.getShortAt(iDirStart + i*12 + 2)];
		oTags[strTag] = oFile.getLongAt(iDirStart + i*12 + 10);
	}
	
	return oTags;
}

function readEXIFData(oFile) 
{	
	var oTags = readTags(oFile, (iOffset+18), (EXIF.TiffTags = {0x8769 : "ExifIFDPointer"}));
	var oEXIFTags = readTags(oFile, (iOffset+10 + oTags.ExifIFDPointer), (EXIF.Tags = {0xA002 : "PixelXDimension",0xA003 : "PixelYDimension"}));
	return oEXIFTags;
}

Thanks.

Thread: Need Help Defining Variables

Thread Tools

Search Thread

Need Help Defining Variables

Bookmarks

Bookmarks

Posting Permissions