Generally speaking, brightness, contrast, saturation and sharpness are thought to be the four simplest controls as they have been developed as long as the color TV was invented in the first place. However, people often turn blind eyes to the fact that all these four controls are related to each other. As a matter of fact, changing any one of these four controls will influence and change the other three.
An image must have the proper contrast for easy viewing. Contrast refers to the difference in brightness between objects or regions. For example, a white rabbit running across a snowy field has poor contrast, while a black dog against the same white background has good contrast. Contrast is specifically defined as the separation between dark and bright, which means that shadows can be darker and highlights can be brighter by changing the contrast. On the other hand, you can decrease the contrast in order to bring the shadows up and the highlights down, which can make them closer to each other. As a matter of fact, adding contrast usually makes the image more popular because it seems more vibrant. In comparison, the image will look duller and boring if the contrast has been decreased to a great degree.
When you have added contrast to an image, then you will notice that some part will become darker while some parts become brighter. This can make the image look more defined. Meanwhile, you have also increased the brightness of some parts. Besides, the saturation of the brighter and darker parts will be increased, which also increases the sharpness. Therefore, it is rather obvious that the four controls do affect each other. Changing of one will also lead to the other three to have corresponding changes. Keep in mind that you need to strike a balance; otherwise, the image will be uncomfortable.