Thanks Emily and Karl for the explanations and illustrations. Halo or
haloing appears to be a natural phenomenon, then.
I wonder why it seems to be seen as an aberration in this review of the
Nikon D300:
"The camera was loved for its “brilliant” image quality, its good colour
balance, low noise and its LCD. However at times the D300 produced some
minor haloing in high contrast areas."
The URL is
http://www.digitalcamerainfo.com/content/Good-Gear-Guide-Reviews-Nikon-D300-16840.htm
Elson T. Elizaga
Nazca Graphic Design & Photography
http://nazca.elizaga.net