The new Photoshop CC 2014 Focus Area is a brand new way to select parts of an image based on the depth of field within an image. The Focus Area is very different from the regular selection tools, these tools tend to work on edge contrast to create the selection. The Focus Area tool will examine the photograph and look for parts of the image in the foreground and isolate those first from layers of Depth of field.
The tool will run in automatic mode initially, but, can be changed later by using the in-focus range slider (marked in Red below).
If the noise level is too high in the background, you can increase or decrease the Image noise level slider. (marked purple).
The output (marked Yellow), of the feature is able to create the following :-
The Focus Area will create a binary result (on the focus plane or not on the focus plane), this can result in a hard mask, the edge can be softened by using the check box (marked in blue). To enhance the output result, the refine edge command can be run and allow you to mark the areas on the cut out to make a more refined selection.
What is the purpose of the Advanced slider – “Image Noise Level”
With the tests that I have made on my own images, this slider is used to tell Photoshop that there are larger amounts of noise in the image and to take this into consideration when making the Focus Area selection. Noise in an image alters the way that blurred parts of the image interact with the sharp areas making difficult to automatically work out where the DOF occurs.
Take this image below
There is no noise in this image and not a large DOF.
Using the Focus Area tool on this image will perform a great starting point, notice how the image noise level is set to auto, and the result is extremely low in this case.
If there is noise in the image (as below)
The Focus Area selection is harder to make when using auto in the image noise level.
If the image noise level slider is increased, then the selection returns back to normal and the foreground figure is selected without a problem