This article is an extract from the Fix It In Photoshop book, which is available as an eBook, paperback, and hardback. Please check out my store for more details. Here is how to use Adobe Photoshop to add motion blur to your background; whilst leaving your foreground intact:
To achieve realistic background blur while leaving our subject sharp, we first need to isolate any subjects we want to remain sharp from the background. There are multiple methods to do this in Photoshop, and you can use any of your favorite methods. I used the Object Selection Tool. Firstly, we need to make some copies of our Background Layer.
STEP 1: Create two copies of the Background Layer by dragging the Background over the Create A New Layer icon at the bottom of the Layers Panel. You can also achieve this via the Application Bar and ‘Layer > Duplicate Layer’.
STEP 2: Now rename the top layer as “Subject Layer” and the middle layer as “Blurred Layer”. You do this by double-clicking the text, or through the Application Bar with ‘Layer > Rename Layer’.
STEP 3: With the “Subject Layer” selected in the Layers Tab, make a selection of the subject or object you want to stay in focus. I used the Object Selection Tool illustrated here and then refined the selection using the Refine & Mask.
STEP 4: Still working on the Subject Layer, we are going to isolate the subject from the background. To keep our changes non-destructive, we are going to isolate the subject using a Mask. Click the Add Mask icon at the bottom of the Layers Tab (illustrated below). Doing the isolation this way means you can always go back later if you need to refine your object selection.
The next process is to delete the subject from the background and then fill in the space where the subject was. The reason we do this step is to avoid ghosting from the foreground object when we add motion to the background.
STEP 5: We need to re-load the Selection of the subject. To do this press and hold Command (on a Mac) or Control (on a PC) whilst clicking the Subject Layer Mask. Next, we need to avoid ghosting from any of the edge pixels on the subject by expanding the selection.
20 to 30 pixels is normally enough, but this depends on the resolution of your original image. From the Application Bar, ‘Select > Modify >Expand’; then enter 20 pixels and press OK to commit the change. Your selection should now look something like this:
STEP 6: Now select the Blurred Layer from the Layers Tab, head up to the Application Bar, and ‘Edit > Content-Aware Fill’. This brings up the dedicated window for this function:
Use a large brush to paint around the selection. This tells Photoshop which pixels it can use for the Content-Aware Fill. The default settings for Content-Aware Fill should be just fine, as we are going to blur the background in the next couple of steps, i.e., it doesn’t matter if the filled area doesn’t quite blend perfectly with the background. So just go ahead and select OK from the bottom of the window to commit the change.
STEP 7: You may notice that Photoshop still has a Selection loaded. Before we apply any effects to our Blurred Layer, we need to deselect the Selection, otherwise, any effect will only occur inside the selected area. Press Command D (on a Mac) or Control D (on a PC). You can alternatively head to the Application Bar and ‘Select > Deselect’.
STEP 8: Before we apply any Filters, it is worthwhile turning the Layer into a Smart Object. This way, we can edit the Filter settings later on if we need to. Make sure you have the Blurred Layer selected, and head up to the Application Bar and ‘Filters > Convert for Smart Filters’
Finally, head back up to the Application Bar again, and this time ‘Filters > Blur Gallery > Path Blur’. You are presented with a dedicated Blur Tools window, and Photoshop places a motion Guide Pin onto your image.
Using the grab handles around the pin, you can set the direction & magnitude of the blur, and from the Panel, you can set the speed of motion; using the Speed slider. Once you are happy with your effect, press the OK button at the top of the window to commit the change.
