When extracting a subject from their background, it's best to think about it in two separate parts.
1. Selecting the body
Photoshop has many tools for creating selections and masks. If the contrast between the subject and the background is high, we may try selecting the subjects with the Quick Selection, Magic Wand or Magnetic Lasso Tool. They can produce fairly accurate edges, which can then be refined further.
The ultimate solution, however, is the Pen Tool. It gives us the most control over the selection we are creating. The Pen Tool creates clipping paths by making points across the image and connecting them. When clicking and dragging, we get curves, allowing us to follow the edges of the figure very accurately. We can easily modify any part of the path we are creating.
- By holding the CTRL/CMD key and clicking on a point or line we can move it around to modify the placement of our selection.
- By holding ALT/OPT and clicking on the path, we can turn any straight line into a curve and vice versa.
As we create curves, anchor points appear, which indicate the direction of the curve and help us predict what the next curve will look like.
When we close our path, we can turn it into selection. There are several ways to do that:
- Using a shortcut: CTRL/CMD + Enter
- Right click and choose Make Selection
- Go to the paths menu, hold CTRL/CMD and click on the path layer
To turn the selection into a mask, simply click the mask button.
Feathering the edges of the mask is important. By default, the edges are very sharp and don't look realistic. To refine them, hit CTRL/CMD + ALT/OPT + R, or locate the Select and Mask/Refine edge feature under the Select tab, then turn up the feathering until the edges are soft enough.
2. Selecting the hair
Basic selection tools do not work well when selecting hair. There are lots of small details in hair edges that need to be cut out relatively precisely, in order for the edited image to look realistic. This is where we use Select and Mask or Refine Edge feature again.
When the hair and background are very similar in color and contrast, we can produce realistic edges. However, that would require using custom hair brushes and painting the hair edges manually.
Having relatively high contrast between the hair and the background is paramount to selecting the hair accurately. In such cases, turn on the Smart Radius and paint around the edges with the Refine Radius Tool. Photoshop will do great job, figuring out where the hair is and make a very precise selection/mask.
As the mask around the subject is ready, all we need to do is paste the new background under the clipped layer. We can then color correct as needed and save our image.