There is provided a navigation device including an image sensor, an analog to digital converter and a processor. The image sensor is used to output an analog image using an exposure time. The analog to digital converter is used to convert the analog image to a digital image using a resolution. The processor is used to identify an image quality of the digital image, and adjust at least one of the exposure time of the image sensor and the resolution of the analog to digital converter according to the image quality thereby adjusting the operation power by changing data length actually processed by the processor.