Does High ISO Cause Noise?


Today’s Question: I enjoyed your article on “Understanding ISO” in the November issue of Pixology. I had seen a video that suggested higher ISO settings don’t actually cause noise. What is your take on that idea?

Tim’s Quick Answer: With most cameras a higher ISO setting will result in more noise in the final image. The video in question focused on the fact that underexposure leads to noise, suggesting that the ISO setting played no role at all. But the ISO setting does impact noise levels.

More Detail: I often see photographers using semantics to try to make a claim that seems to contradict established knowledge in photography. This generally seems focused more on getting viewers to watch a video rather than on truly helping them understand an issue.

When you raise the ISO setting on a camera in order to maintain the same exposure you need to either use a faster shutter speed or use a smaller lens aperture. In other words, at a higher ISO setting you are capturing an image that is underexposed and then brightening the image through amplification.

It is true that underexposing an image will result in more noise. It is also true that amplification will result in more noise. But the fact of the matter is, increasing the ISO setting will increase noise levels with most cameras (a small number of cameras are ISO invariant, which mostly means they have excellent noise performance overall).

In addition, it is worth noting that using the ISO setting to increase the overall exposure is better than underexposing an image without raising the ISO setting. That is because in-camera amplification of the signal recorded by the image sensor results in less noise that post-capture brightening of the image.

So, raising the ISO setting will increase noise levels for most cameras in most circumstances. But generally speaking, the benefit of raising the ISO setting is greater than the risk of noise, in terms of being able to ensure a fast enough shutter speed to avoid motion blur or not having enough depth of field.

You can learn more about the ISO setting as it relates to exposure in the November 2021 issue of Pixology magazine. If you’re not already a subscriber, you can learn more about Pixology on the GreyLearning website here: