One major advantage of digital cameras: You can change the ISO speed for any shot
Lower ISO speeds for higher image quality
Noise becomes noticeable at ISO 3200
Changing the aperture affects the depth of field, while changing the shutter speed affects the freezing or blurring of motion. And changing the ISO speed affects the picture quality. See photos above, the ISO speed affects the graininess of the image. The higher the ISO speed, the grainier the picture will look. Lower ISO speeds produce less grain.
This grain is called noise. High ISO speeds result in more noise in the image. The latest digital SLR cameras use various technologies to reduce this noise, so the image quality is still quite good even at very high ISO speeds.