There any many ways to dim the background when you want to put more emphasis on your subject in the foreground. Whether using flash sync speed, using Lightroom radial filter or adjustment brush, all serve the same purpose; to let your viewers focus more on the subject while dimming the background and reducing clutter and unwanted details.
For this tutorial we are going to look at how to achieve this quickly and easily using Photoshop.
Open the candidate photo
We will select a photo with a busy background that to apply this tutorial on. Our objective again is to darken the background.
Add Levels adjustment layer
Even in Photoshop there are many ways to achieve this. We chose the simplest and most effective way for this tutorial. So, first duplicate the background layer and then, in the Layers palette, choose New Adjustment Layer.
Select the Levels adjustment layer and start by moving the middle slider towards the right. Stop and release when you reach the dimmed effect you like. Keep your eyes on the background while you drag the slider and disregard the subject. The adjustment layer darkened the entire image but don't worry if your subject became too dark. We will next add a layer Mask to bring it back to the brightness level you want.
Add a white Mask to the adjustment layer
The next logical thing is to hide the areas we don't want darkened (in this case our person). Easy... Click on the layer mask and make sure it is selected. A white border shows that it is activated.
Black hides / White reveals
Remember that we have created a white background mask... In Photoshop masks, white reveals and black hides. So click on the "D" key on your keyboard to bring back the default white foreground and black background to the color picker. Hit the "X" key to invert so that black is now your foreground color.
Select a less than 50% Opacity, middle-sized brush ("B") and start painting on your subject to hide the darkened effect from the face and body. It is also a good idea to lower the Flow to 50% to build on the effect step after step. In case you made a mistake reverse the brush foreground color to white by pressing the "X" key again.
Here’s what my image looks like after brushing the subject with white to reveal the exposure highlights. The result is a flash high-sync similar effect.
Dimming the background is a simple and effective technique to hide busy backgrounds. For a quicker processing though I prefer the newly introduced Radial Filter in Lightroom 5. Check out this tutorial on using the Radial Filter tool in Lightroom.