ISO Settings
ISO denotes the sensitivity of a digital image sensor to light. Increasing ISO amplifies the signal from the sensor, allowing for faster shutter speeds or smaller apertures in low-light conditions, but simultaneously amplifies electronic noise.
Core Mechanics
- Signal Amplification: ISO adjusts the gain applied to the analog signal before it is converted to digital data.
- Native ISO: The base sensitivity range of the sensor where dynamic range and signal-to-noise ratio are optimal (typically ISO 100–400).
- Expanded ISO: Settings below (Low) or above (High) native range, often resulting in reduced dynamic range or increased noise.
Noise and ISO Interaction
- Digital Noise: Random variation of brightness or color information in images, primarily consisting of:
- Luminance Noise: Grain-like texture affecting brightness.
- Chrominance Noise: Colored speckles, generally more objectionable than luminance noise.
- Inverse Relationship: Higher ISO settings exponentially increase noise floor, degrading image quality.
- Trade-offs: Using higher ISO is often preferable to underexposing an image and brightening it in post-processing, as modern sensors handle high ISO amplification better than shadow lifting.
Best Practices & Mitigation
- Expose to the Right (ETTR): Maximize exposure without clipping highlights to optimize signal-to-noise ratio.
- Native Range Preference: Stay within native ISO whenever possible.
- Post-Processing: Noise reduction is more effective on luminance than chrominance; color noise should be addressed first.