Yii team released minor version of Imagine extension.

The only change is that Image::thumbnail() could now automatically calculate thumbnail dimensions based on aspect ratio of original image if only width or only height is specified. Image::$thumbnailBackgroundColor and Image::$thumbnailBackgroundAlpha are introduced to be able to configure fill color of thumbnails.

Note that this is likely last 2.0.x version so make sure your composer.json is in order.