Which form of image noise results from underexposure?

The form of image noise that results from underexposure is mottle. This occurs when there is insufficient light reaching the imaging receptor, leading to a lack of detail in the darker regions of an image. Underexposed images often exhibit uneven brightness and contrast, which contribute to a blotchy or patchy appearance — characteristics that are described as mottle.

Underexposure can result in an uneven distribution of the signal, where the noise becomes more prominent in the shadow areas since there isn't enough exposure to adequately illuminate these regions. Thus, mottle is recognized as a specific type of noise that is particularly related to the quality of the exposure, making it directly linked to the issue of underexposure.

Other forms of noise like static, graininess, and blurriness arise from different causes. Static can come from electronic interference or random variations, graininess is often related to film speed and is not strictly a result of exposure, and blurriness typically is due to motion or focus issues rather than exposure levels.