AN ACTION CAN REMOVE THE DRUDGERY OF APPLYING a sequence of steps to one image, but it's still drudgery if you have to run that action over and over again on 100 images. Fortunately, there's no need to put up with that in Photoshop, because you can use the Batch command to apply a Photoshop action to any number of files. You can also save a batch process as a dropleta batch action saved as a shortcut. Just drop documents on the droplet to process them.
Although the Batch command is powerful, it's also a little on the complex side. Photoshop also includes the Image Processor, a more user-friendly batch processor that focuses on a few common conversion tasks.