Do you playing with Photoshop often?! Since you’re reading this blog Im sure yes, so you’re playing with Levels often too right? Here is a little known levels trick helping you keep eye on the clipping parts of the picture. In other words you can keep eye on threshold of the picture while making correction with Levels.
Here is the trick - you got a picture and you’ve opened Levels. While you moving one of the sliders of the input levels press and hold alt key and you will see live preview of the clipping parts ( threshold ) of the picture.