Use a constant to define the default thumbs location.

DependencyInjection/Configuration.php

@@ -2,6 +2,7 @@
 
 namespace Beryllium\Icelus\DependencyInjection;
 
+use Beryllium\Icelus\ImageService;
 use Symfony\Component\Config\Definition\Builder\TreeBuilder;
 use Symfony\Component\Config\Definition\ConfigurationInterface;
 
@@ -21,7 +22,7 @@ public function getConfigTreeBuilder()
 
         $rootNode
             ->children()
-                ->scalarNode('prefix')->defaultValue('/_thumbs')->end()
+                ->scalarNode('prefix')->defaultValue(ImageService::DEFAULT_PREFIX)->end()
                 ->scalarNode('output_dir')->defaultNull()->end()
             ->end();
 

ImageService.php

@@ -17,21 +17,23 @@ class ImageService
     public $prefix;
     public $completed = array();
 
+    const DEFAULT_PREFIX = '/_thumbs';
+
     /**
      * Constructor
      *
      * @param Imanee        $imanee         Performs the required image manipulations
      * @param string        $source_dir     Where to find the images
      * @param string        $output_dir     Where to save the images
-     * @param string        $prefix         prefix path for images
+     * @param string|null   $prefix         subdirectory under output_dir to save the images (Default: '/_thumbs')
      * @param Filesystem    $filesystem     Filesystem class for doing filesystem things
      */
     public function __construct(Imanee $imanee, $source_dir, $output_dir, $prefix, Filesystem $filesystem)
     {
         $this->imanee     = $imanee;
         $this->source_dir = rtrim($source_dir, '/');
         $this->output_dir = rtrim($output_dir, '/');
-        $this->prefix     = $prefix;
+        $this->prefix     = $prefix ? rtrim($prefix, '/') : static::DEFAULT_PREFIX;
         $this->filesystem = $filesystem;
     }
 

README.md

@@ -48,14 +48,16 @@ __Note:__ The class name should be a string, not an object instantiation. (This
 Configuration
 -------------
 
-Add to `sculpin_kernel.yml`
+Generally, no additional configuration is required. If you want to rename
+the output subfolder for thumbnails (default is 'yourblog.com/_thumbs'),
+add this to your `sculpin_kernel.yml`
 
 ``` yml
 icelus:
     prefix: '/_thumbs'
 ```
 
-* `icelus.prefix` : A part of the path used as the prefix of the output path. default is `'/_thumbs'`.
+* `icelus.prefix` : A subdirectory under the Sculpin output directory to store the thumbnails. Default is `'/_thumbs'`.
 
 Usage
 -----