code: public BlurBuilder brightness(float brightness) {
          data.preProcessors.add(new RenderscriptBrightnessProcessor(data.contextWrapper.getRenderScript(), brightness, data.contextWrapper.getResources()));
          return this;
      }
docs: Set brightness to  eg. darken the resulting image for use as background
  
  @param brightness default is 0, pos values increase brightness, neg. values decrease brightness
  .-100 is black, positive goes up to 1000+