public function removeCoverImage()
    {
        $sizes = $this->_mixer->getValue('sizes');

        if (empty($sizes)) {
            $sizes = explode(' ', 'original large medium');
        } else {
            $sizes = array_keys($sizes);
        }

        foreach ($sizes as $size) {
            $file = $this->_mixer->getCoverFile($size);
            $this->_mixer->deletePath($file);
        }

        $this->set('coverFilename', null);
    }