The first step is to look at the channels palette and determine which color channel best represents the area we want to capture. To the right, shown from top to bottom, you can see the red, blue, and green channels for this image. It's obvious that the red channel contains the most information for capturing the fireworks. In the channel palette, click on the red channel and drag it down to the new channel button. This creates a duplicate of the red channel as an alpha channel.
Alpha channels are a way of saving selections that can be loaded at any time.
In addition, they can be edited with painting tools like a grayscale mask . You want to be sure that your alpha channel is the active channel before you start painting. Now we have a grayscale mask that can be loaded as a selection for isolating the fireworks. Click on RGB in the channel palettes to make all channels active and return to the color view of your image. Next from the Selection menu, choose Load Selection.