code: public function brightness( $value, $region = null )
      {
          if ( $value < - 255 || $value > 255 )
          {
              throw new ezcBaseValueException( 'value', $value, 'int >= -255 && int <= 255' );
          }
          // 0 = -255
          // 50 = half as bright = -127
          // 100 = regular brightness = 0
          // 150 = 127
          // 200 = twice as bright = 255
          $value = ( 200 * ( $value + 255 ) ) / 512;
  
          $this->setRegion( $region );
          $this->addFilterOption( $this->getActiveReference(),
              '-modulate',
              $value
          );
      }
docs: /* (non-PHPdoc)
  @see extension/ezie/autoloads/eziezc/interfaces/eZIEEzcConversions#brightness($value)