[opendtv] Re: RGB mania
- From: Henry Baker <hbaker1@xxxxxxxxxxxx>
- To: Allen Le Roy Limberg <allimberg@xxxxxxxxxxxx>
- Date: Tue, 18 Jan 2005 09:46:46 -0800
Re "semi-log":
A function that is linear about the origin, and which becomes logarithmic
away from the origin, and which is symmetric about the origin is the
inverse hyperbolic sine function (arcsinh/asinh). This is a more-or-less
ideal "companding" function, and approximations to it appear in voice
applications
(the US & International 8-bit telephone voice standards), as well as in some
proposed video standards. But those approximations aren't "smooth", whereas
the arcsinh function itself is very smooth, and can therefore be used with
8-bit, 10-bit, 12-bit & higher depths without additional standards activities.
This may well be the _only_ good use for the asinh library functions found in
C/Fortran/etc. ever found!
At 07:41 AM 1/18/2005, Allen Le Roy Limberg wrote:
>The "semi-log" properties of analog TV signals concern more than display
>characteristics and camera characteristics. These properties are probably
>important in the practical transmission of TV through a radio link; there
>may be an expert in TV broadcasting that can comment on this. In regard to
>receiver design, these properties facilitated the use of automatic gain
>control in vacuum-tube TV receivers without distorting the video signal too
>much. This is one reason the analog TV system design deferred gamma
>correction until the TV receiver.
>
>Al Limberg
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