Image conversion generally includes converting a color image to a gray or binary one, splitting and merging the RGB color channels, and using the image palette to apply pseudo color to a gray image.
Color to gray conversion is useful when we are only interested in the intensity of a color image. When our printer or any other output device does not support color, we can perform the conversion so as to know how the image will look like after output. For some recognition system that works only with gray images, this kind of conversion is necessary to be done.
Any color image can be spitted into its Red, Green, and Blue color channels. Then you can process each channel separately and recombine them into a new color image. This feature is especially useful when the object you want to process is located in one channel only.
Pseudo color does not add additional information to the original image. However, it helps to make some details more visible to human eyes. This feature is commonly used for viewing sensor images, such as satellite images.