Isolate Objects with Masking

There are loads of isolation techniques in Photoshop. Designers normally use
Lasso tool to outline the edges of an object or the Eraser Brush to remove
pixels from edges. Some use Quick Make mode or Pen Tool to select and layer a
mask. But the final result may not be very good, especially with moving objects.
The complexity and fine details of the object demand time to separate this

image from its background. This is where the Masking technique becomes suitable,
especially for moving objects on a dark background, for example, you have an
image of a flying bird on a black background that you would like to put up
against a clouded sky. Before you start selecting the bird, arrange its flying
position according to your new background and do the required color correction
for matching the new background. For this you can use levels or curve tools.

First, we will start with luminosity of this RGB image. For this, press 'Opt/Alt + Command/Ctrl + ~' and save the selection to a new channel by clicking 'Select >Save Selection'	Go to new channel and use levels or curves to eliminate mid tones in the new mask, preserving only the darkest edges. You can also use Paint Brush to clean up the new mask channel

Select the new channel and go back to your RGB composite. Select the Move Tool from tool palette and drag the selected area onto the new background	The feather edges and the semi-transparent areas are too dark as they contain some black color because of the original image background. Lighten it using Dodge Tool in Shadow mode