Re: 6502 core / 128 mode (re: J-Board) (fwd)

From: Christopher A Bongaarts (
Date: 2001-03-16 21:11:27

As once put it so eloquently:

> The amiga video port has a /PIXELSW as well as a XCLKEN signal pair.  If you
> separate the sync from your video signal, take the horiz and synthesize
> 28mhz (?) from it, and feed it into the video port, and take your separated
> horiz and vert sync's and feed them into the output with XCLKEN, the amiga
> will switch its internal oscillator off and use yours so it can sync to your
> signal.  Now all you need to do is switch between the amiga and your video
> signal. ;) Thus, PIXELSW.  Whenever a non-background color is displayed,
> pixelsw indicates that amiga video is active.  Voila. Genlock.
> Amigas have been able to do chroma keying via an addin card and time base
> corrector.  This, however, isnt stock hardware.

Putting on my television production hat...

"Genlock" is a generic video term for synchronizing multiple video
sources to the same clock generator (generator lock, hence the name).
Every piece of professional video equipment (cameras, time-base
correctors, special-effects generators/switchers) has a genlock
input.  Some also have a "black burst" output signal that is fed into
the genlock input of other devices.

"Keying" is cutting out a portion of the video signal like a
cookie-cutter.  Typically, you then "fill" the keyed-out area with
another video signal.  "Chroma keying" is keying out a specific
color.  "Luma keying" is keying based on the luminance (brightness) of 
the signal.

"Genlock overlay" is usually how the computer folks refer to doing
chroma keying, using the background color of the computer as the key
and the computer video as the fill video.  So it looks like the input
video is the background, and the non-background computer video is
overlaid on top.

Chroma keying based on the input video itself requires extra hardware,
as others have said.

%% Chris Bongaarts    %%  %%
%% Univ of Minnesota  %% CBongo on EFnet IRC  %% Stop Plate Tectonics!
This message was sent through the cbm-hackers mailing list.
To unsubscribe: echo unsubscribe | mail

Archive generated by hypermail 2.1.1.