code: public function contrast( $value, $region = null )
      {
          if ( $value < - 100 || $value > 100 )
          {
              throw new ezcBaseValueException( 'value', $value, 'int >= -100 && int <= 100' );
          }
  
          $round_value = round( $value / 10 );
  
          if ( $round_value >= 0 )
          {
              $option = '-contrast';
          }
          else
          {
              $option = '+contrast';
              $round_value = - $round_value;
          }
  
          $this->setRegion( $region );
          for ( $i = 0; $i < $round_value; ++$i )
          {
              $this->addFilterOption(
                  $this->getActiveReference(),
                  $option
              );
          }
      }
docs: /* (non-PHPdoc)
  @see extension/ezie/autoloads/eziezc/interfaces/eZIEEzcConversions#contrast($value)