There may be times when you want to take one of the color channels and create a new document from it. Use cases might be making a monochromatic image or displacement map. The easiest way to do this is in the Channels panel (Window>Channels). Click on one of the channels to make it active, and then Right-click it and choose Duplicate Channel. Under the Document drop-down menu in the Duplicate Channel dialog, choose New. You can name it here if you want; if not, name it when you save it. Click OK and a new document will be created. 

This tip originally published in Colin Smith’s “Photoshop Tips” column in the January, 2023 issue of Photoshop User magazine.