Path: utzoo!attcan!utgpu!watmath!clyde!att!mtuxo!lzfme!jwi
From: jwi@lzfme.att.com (J.WINER)
Newsgroups: comp.graphics
Subject: Re: ShowScan quality image bit rate
Summary: Dynamic range of film and TV
Message-ID: <1133@lzfme.att.com>
Date: 16 Feb 89 18:23:48 GMT
References: <146@mlogic.UUCP> <2569@eos.UUCP>
Organization: AT&T, Lincroft NJ
Lines: 31

In article <2569@eos.UUCP>, jbm@eos.UUCP (Jeffrey Mulligan) writes:
> From article <146@mlogic.UUCP>, by bennett@mlogic.UUCP (Bennett Leeds):
>  
> 
> > The point is that the
> > "dynamic range" of film is much greater than TV.
> 
> Is this true?  I'm not necessarily doubting it, it's just that the dynamic
> range of [color] film is not all that large to begin with; I would guess
> something slightly more than 1 log unit.  What are the units that are
> used to describe this?  Gamma?  Anybody have any hard numbers?  Presumably
> this is part of the NTSC standard.
> 

TV has a range of about 5 f-stops while film has up to 7 f-stops.
This translates to more detail in the shadow and in the light tones,
i.e. lower contrast.  If you assume that TV is capable of 256
graylevels between black and white, then 2 extra f-stops would mean
that film is capable of 1024 gray levels between the same black and
white.  Since a "normal" scene has about 7 f-stops of range film
will capture it while on TV anything above a certain level goes all
white and anything below a certain level goes solid black.  This is
most ovbious when a film is shown on TV -- a dark scene that would
be visible in the theater goes almost black on the TV.

I'm not sure that the technical definition of an f-stop would be
useful except to note that a bigger lens opening has a smaller
number, and that an increase (decrease) amounts to double (half) the
amount of light.

Jim Winer MT 4G-429 ..!lzfme!jwi