STEP THREE: When you’re done, press Enter to apply the filter. Now you can further control the blur using the smart filter’s mask. To do so, click the Smart Filters thumbnail, choose the Brush tool (B), press D then X to set the Foreground color to black, then paint over the areas where you want to remove the blur. If you make a mistake, press X to set the Foreground color to white, paint any areas that you want to blur again, then press X to set the Foreground back to black and continue.