On “light”-related aspects:

“Tones and colors do NOT always record exactly what the camera lens saw.”

Often the brightness, contrast, and color balance in a photograph will more accurately depict “what the camera lens saw” if those aspects undergo some post-exposure changes* (so TTG allows those changes).

Don’t worry: most devices record “light”-related aspects well enough most of the time for the result to qualify as TTG without further changes.

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*In some cases — for example when a scene is recorded on negative film — the tones and colors may have to be radically changed to depict “what the camera lens saw.”