Every type of light imparts a color cast. Be it the incandescent light in your living room or the fluorescent bulb in the drawing room or even the Sun. This color cast becomes a bit of an issue when you look at them on the computer screen or make a print. Your images are either too orange or too blue.
White balance is the name of an adjustment process wherein an image is treated to display the color white as it should be, sans the color cast.
In the process, the rest of the colors are also corrected for any color cast. The process is sometimes also referred to as gray balance. This is because the process involves displaying neutral colors such as white and 18% gray as they are – neutral. 18% gray has an average reflectance and photographers routinely use an 18% gray card as a reference when shooting in changing light. This allows faster correction of the color cast when post-processing.
The manual mode is often referred to as the ultimate in creative photography. Why? Because manual mode allows you to use your intuition in order to set the aperture and shutter speed on your own. In other words, you are no longer dependent on the camera’s built-in metering system to dictate what exposure values you need to dial in (normal Auto mode).
The manual mode is necessary when you have to control both the amount of light as well as the depth of field of your shots. Let’s take a couple of examples. Let’s say that you want to shoot a seascape. You need to use a small aperture and then drag the shutter speed to produce the right exposure and composition. Similarly, if you need to use a wide open aperture in broad daylight in order to blur the background, something that the built-in meter will not allow, you can use an ND filter and open up the aperture wide to achieve that.