Contrast Adjustments in 8-Bit versus 16-Bit Images
Make the same Levels adjustment to a 16-bit image and reopen the Levels dialog box.
Contrast the previous adjustment on an 8-bit image with the same adjustment applied to a 16-bit image. After making the same Levels adjustment and reopening the Levels dialog box, you find a much different result. Notice the histogram displays a solid tonal range with no gaps in the graph.