Step 4: Apply The Gaussian Blur Filter

We need to soften the edges of our selection to create a smooth transition between the selected and unselected portions of the photo, and the Quick Mask mode is going to make it very easy for us to see what we're doing. We'll use Photoshop's Gaussian Blur filter to soften the edges. Go up to the Filter menu at the top of the screen, choose Blur, and then choose Gaussian Blur:

This brings up the Gaussian Blur dialog box. Keep an eye on the selection edges in the document window as you adjust the Radius slider at the bottom of the dialog box. Dragging the slider to the right will increase the amount of blurring along the edges, increasing the edge softness, while dragging it to the left will decrease the amount of blurring. Adjust the Radius value until you see a nice, smooth transition along the edges. Here, I'm increasing my Radius value to somewhere around 16-17 pixels. The value you end up using may be different depending on the size of your image:

Click OK when you're done to exit out of the dialog box. Here we can see the smooth transition area around my selection edges:

Step 5: Exit Out Of Quick Mask Mode

Now that we've softened our selection edges, we can exit out of Quick Mask mode and go back to Standard mode. To do that, either press the letter Q on your keyboard once again or click on the Standard Mode icon in the Tools palette:

You'll see the red overlay disappear in the document window and your selection outline returns:

Step 6: Save The Selection

We've done everything we need to do with our selection. Now we need to save it. To do that, go up to the Select menu at the top of the screen and choose Save Selection:

When the Save Selection dialog box appears, just click OK in the top right corner to exit out of it. There's no need to name the selection:

Press Ctrl+D (Win) / Command+D (Mac) to deselect your selection in the document window. If you switch over to your Channels palette, which you'll find grouped in beside the Layers palette, you'll see that your selection has been saved as a new alpha channel named Alpha 1 at the bottom of the palette. We can see by looking at the channel's preview thumbnail on the left that the area that was inside the selection appears white, while everything that was outside the selection appears black. It's tough to make out in the small thumbnail, but the smooth transition area we created around the selection edges appears as a narrow white-to-black gradient:

This is important because in a moment, we're going to be using this black and white alpha channel we've created as a depth map for the Lens Blur filter. A depth map is simply a grayscale (black and white) image that Photoshop uses with the Lens Blur filter to decide which parts of the image to blur out and by how much. Any areas in the depth map that are pure black remain 100% in focus while areas that are pure white are completely blurred out. Areas that fall between pure black and pure white, such as the transition area around the selection edges, will be blurred to a lesser degree depending on how light or dark they are.

If you were paying attention there, you may be thinking "Wait a minute, isn't that exactly the opposite of what we want? You said black areas remain in focus while white areas are blurred out, but in the alpha channel we just created, it's the white area that we want to keep in focus, not the black area. The black area is where we want to apply the blurring!" You're absolutely correct. We'll need to tell Photoshop to invert our depth map in the Lens Blur filter's dialog box, and we'll see how to do that in a moment.

Switch back over to your Layers palette to continue.