Angus Dorbie (dorbie++at++bitch.reading.sgi.com)
Sat, 18 Jan 1997 17:19:45 +0000
> > The images in the URL show this Mach effect:
> >
> > ____________ __________
> > | /
> > | /
> > | |
> > | |
> > | /
> > ______________| _________/
> >
> > actual intensity perceived intensity
^
|
Yep, this graph is wrong and actually shows |
the opposite of the effect! _____________________|
I must have had my receptors mixed up when I drew it :-)
Still, both the posted URLs seem to reffer to the corrected graph
above and not the mach banding effect in the graph below and
now that I've checked Foley & Van Dam, both are described as
examples of Mach banding. Even if the Foley example deviates a
little from my graph below.
I've resisted the temptation to post a gif of the effect below.
Cheers,
Angus.
> >
> > And I thought Mach banding was:
> > __
> > ____________ / \_________
> > / /
> > / /
> > / /
> > / /
> > / /
> > / /
> > actual intensity perceived intensity
> >
> > Graph axes guide:
> >
> > (intensity)
> > ^
> > |
> > |
> > |
> > -------> (space)
> >
> > Hence a percieved intensity band where none exists, often seen in
> > graphics when intensity gets clamped to a maximum value.
> >
> > Any takers for this Fridays pub trivia question? I think Foley van Damn
> > is where I remember these graphs from but my copy is at home.
> >
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