画像ファイルのサイズ取得とサムネイル作成

gistfile1.js

var createPreview = function(file, image, callback) {
    var canvas = $('<canvas>')[0];
    var context = canvas.getContext('2d');
    var width = image.width;
    var height = image.height;

    if (image.width > previewOptions.maxWidth) {
        width = previewOptions.maxWidth;
        height = previewOptions.maxWidth / image.width * image.height;
    }

    if (image.height > previewOptions.maxHeight) {
        height = previewOptions.maxHeight;
        width = previewOptions.maxHeight / image.height * image.width;
    }

    canvas.width = width;
    canvas.height = height;

    context.drawImage(image, 0, 0, width, height);
    file.preview = canvas.toDataURL(file.type);
    callback(); 
};

var loadImage = function(file, callback) {
    var reader, image;

    reader = new FileReader();
    image = new Image();
    image.onload = function() {
        file.width = image.width;
        file.height = image.height;
        createPreview(file, image, callback);
    };
    reader.onload = function() {
        image.src = reader.result;
    };
    reader.readAsDataURL(file); 
};