Contrast - emphasizes the differences between light and dark. 

Adjusting of Contrast:

• Positive value will make the shadows darker and the highlights lighter.
• Negative value will lighten the shadows and darken the highlights.

Gamma Correction - function adjusts the general brightness of the image for mid-tone and shadow.

• Gamma is the difference in contrast between the light tones and dark tones of an image.

• Any change you make in the gamma level only affects the mid-tones of the image.