Why does higher ISO cause image noise?
Referring to the diagram and discussion in the previous article it is worth noting the in the digital world ISO is the level of sensor signal amplification.
So when the signal is amplified the inherent noise is also amplified hence the noise.
High ISO noise factors:
- Higher ISO: The greater the ISO the more noise in a linear fashion due to amplification
- Low light: The less light there is means the signal levels are closer to the noise levels hence you see more noise
- Pixel size on the Sensor: Bigger pixels in general equal less noise
- Sensor Temperature: At higher temperatures you generally find higher noise
- Signal processing in the Camera: Both the analogue and digital processing inside the camera makers makes a significant difference to the image noise inclduing the type of noise dispalyed
- Exposure: Under exposing will increase noise - so expose corretcly of slightly over expose in high ISO scenarios
- Sensor size and Resolution: Larger sensors generally have less noise and higher megapixel cameras typically have more noise than lower MP cameras for the same sensor size due to pixel size
- A smaller sensor with a higher megapixel count means more noise
Keep these things in mind when trying to minimise noise in your images.