Contrast Stretching
Below is an example of contrast stretching. The histogram's shape is the same, but stretched, hence it is also called histogram stretching.
Contrast enhancement is a technique to make objects in an image easier to distinguish.
Below is an example of contrast stretching. The histogram's shape is the same, but stretched, hence it is also called histogram stretching.
Below is an example of histogram equalization. Each intensity level is mapped (red) to make the histogram equalized. Note that the cumulative histogram (blue) is approaching a straight line.
Image used: "Unequalized Hawkes Bay NZ" by Konstable (CC BY 2.0); edited from Phillip Capper (CC BY 2.0)