Which statement about ISO and noise is true?

• A. Higher ISO reduces noise
• B. ISO has no effect on noise
• C. Lower ISO increases noise
• D. Higher ISO increases noise

Answer: (D)

Understanding ISO involves recognizing that it controls how much the sensor’s signal is amplified to create a brighter image. When you raise ISO, the camera boosts the signal more to achieve the same exposure, but that amplification also boosts random variations—noise—in the signal. The result is a grainier image with more noticeable color speckling, especially in darker areas. Lower ISO uses less amplification, so the image stays cleaner with less visible noise, provided you have enough light or a longer exposure to achieve the desired brightness. The statements that higher ISO reduces noise, or that ISO has no effect on noise, don’t align with how amplification amplifies both the signal and the noise.