// promise hell
ImageProcessor.prototype.execResizeImage = function ImageProcessor_execResizeImage(option, imageData) {
    return new Promise(function(resolve, reject) {
        var resizer = new ImageResizer(option.size);

        resizer.exec(imageData)
        .then(function(resizedImage) {
            var reducer = new ImageReducer(option);
            reducer.exec(resizedImage)
             .then(function(reducedImage) {
                 resolve(reducedImage);
             })
             .catch(function(message) {
                 reject(message);
             });

        .catch(function(message) {
            reject(message);
        });
    });
};