What is ISO?
Strictly speaking, ISO is a Switzerland-based standards body whose name derives from the greek word for `the sameī. It is not an acronym, since the letter order would change in different languages, hence it shouldnīt be pronounced as a series of letters.
ISO is the name given to what`s commonly called `sensitivity` in photography. Itīs analogous to the system used in film but has a few fundamental differences, and these differences have been increasing over time.
Lightness
Throughout this article we use the term `lightness` to express how light or dark the final image is. This is to make clear that we`re discussing a representation on a white to black tonal scale, not a measure of emitted light. How `bright` any tone specific tone appears to a viewer would depend on the display it`s viewed on.
At its most simple, ISO tells us that using specific exposure settings at a given illuminance level should give an image that looks like we expect it to. For many circumstances, this is all you need to know. Itīs still a close-enough analogy for the film standard that a film-era light meter will still work for digital. Give or take.
But it`s often assumed that increasing ISO just adds amplification (voltage gain applied to the analog signal coming from the pixels), a bit like turning up the volume on an audio amplifier. This is not true, and this misunderstanding can make it harder to understand what your camera is actually doing. Virtually all modern cameras have at least one mode or function that diverges from the ISO = Amplification concept, so put that idea aside.
Seriously, what is ISO?
ISO in digital cameras (specifically ISO standard 12232:2019) is designed to resemble the ASA film speed standard that was adopted by the International Organization for Standardization in 1974.
ISO describes the response of the whole processing pipeline, relating exposure to end image lightness
However, there is a fundamental ...
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