less.js/lib/less-node/image-size.js

var Dimension = require("../less/tree/dimension"),
	Expression = require("../less/tree/expression"),
	functionRegistry = require("./../less/functions/function-registry"),
	path = require("path");

function imageSize(filePathNode) {
	var filePath = filePathNode.value;
	var currentDirectory = filePathNode.currentFileInfo.relativeUrls ?
		filePathNode.currentFileInfo.currentDirectory : filePathNode.currentFileInfo.entryPath;

	var sizeOf = require('image-size');
	filePath = path.join(currentDirectory, filePath);
	return sizeOf(filePath);
}

var imageFunctions = {
	"image-size": function(filePathNode) {
		var size = imageSize(filePathNode);
		return new Expression([
			new Dimension(size.width, "px"),
			new Dimension(size.height, "px")
		]);
	},
	"image-width": function(filePathNode) {
		var size = imageSize(filePathNode);
		return new Dimension(size.width, "px");
	},
	"image-height": function(filePathNode) {
		var size = imageSize(filePathNode);
		return new Dimension(size.height, "px");
	}
};

functionRegistry.addMultiple(imageFunctions);