An image in which tonal reproduction is the reverse of that of the subject.
Neutral-density filter
A filter that reduces light intensity without changing colour balance.
Newton's rings
Interference patterns seen when optical surfaces are placed on top of one another - typically when transparencies a held between two sheets of glass.
Noise
Unwanted signal disturbance caused by thermodynamic or mechanical instability particularly in scanners and digital cameras. Such noise tends to reduce the amount of useful data recorded.
