Exposure is basically how bright or dark your image is. We call an image that’s too bright overexposed and the image that’s too dark underexposed. Sometimes, only parts of an image are underexposed or overexposed.
Aperture, shutter speed, and ISO affect the exposure. They also affect other aspects of your image such and motion blur, grain and sharpness of the image.
Note that sometimes overexposing or underexposing parts of an image is an artistic choice. The photograph above is an example of what's called low-key lighting: parts of an image are intentionally underexposed to enhance shadows and create a particular mood.Next: Depth of Field go back