A camera captures an image, which is then displayed on your screen. The image taken by the camera is not always the same as that displayed on your screen.
Every monitor has an intensity to voltage response curve which is roughly a 2.5 power function. This means that when you supply a voltage of x, the intensity is x to the power 2.5. Hence the monitor would display the image darker than it actually is.
To account for this error, we have to introduce a correction, known as gamma correction into the input signal to the monitor. The following image is the best explanation of what it does.
