Histogram

Choose Adjust > Levels to view the tonal range of the image.

In the above example the image has more shadows than highlights.

In the above example the image has more highlights than shadows.

Black and White Points

Properly exposed picture should span over the entire range 0 to 255. 0 is the black point - minimum luminosity of a pixel at the left edge of the histogram and 255 is the white point - maximum luminosity at the right edge.

Proper exposition

Incorrect exposition (missing shadows and highlights)