Brightness and contrast is a staple for most image editing software. Brightness increased either the lightness or darkness of the whole image. Increasing the contrast makes the light areas lighter and the dark areas darker.
In the option section you can use either the sliders or the arrow buttons to adjust the brightness and contract between plus and minus 128. The results will be displayed below on the right hand side
Contrast stretch, or Normalisation as it’s often called, is an operation that spreads out the contrast of an image across the entire available range using a linear scaling function. There aren’t any options for this clarification.