Posted by Mike Kujbida on 10/02/05 18:59

Rick Merrill wrote:
> Mike Kujbida wrote:
>
>> If you're familiar with the chromakey technique (think TV weather
>> person), then this analogy will help.
>> The "key" is the hole that is cut (what's left of the greenscreen,
>> excluding the weather person, after some electronic adjustments are
>> made) and the fill is what replaces the green screen (satellite map,
>> location shot, etc.). Does that help?
>>
>> Mike
>>
>
> So why would one want the key(hole) to be on one channel and the
> fill(background) on another? How would this be used to put a 'bug' on
> screen?


The key typically has something called an alpha (transparent) channel. This
means that anything NOT part of the 'bug' will not be seen. The 'fill'
(backgound) is what is being keyed over top of. Assuming the key is a title
or station logo, it could thenbe place over the program stream without
anything else in the key showing. For example, I use a lot of logos that
are on a plain white background. I bring them into Photoshop and make the
white background transparent. This way, I cam now 'key' the logo over top of
anything I want.
The following links may help explain what an alpha channel is:
http://www.ttop.com/how_to_alpha.html
http://www.digitaljuice.com/techsup/alphachannels.asp
Does that help or further muddy the waters?

Mike


>>
>> The 2000 will support a “Key/Fill” mode for
>> Targa frames, (automatic)
>> MPEG-2 files, and (user)
>> DV files. (user)
>>
>> For example, loading a file named "Logobug" on Channel 2
>> automatically loads the Logobug_ (Alpha Clip) onto Channel 3.
>>
>> For Targa files, the alpha clip name will be generated automatically
>> during ingest via FTP. For DV and MPEG files, the user must
>> use the same name as the 'fill channel' and explicitly save the alpha
>> clip adding the underscore to the end of the clip – all prior to
>> transfer.
>>
>> In Key/Fill mode, the transport controls of Channel 2 will
>> control Channel 3, allowing 1x frame-synced playback of both Key and
>> Fill channels. This mode will be invoked by clicking a check box in
>> the GUI. Channel 1 will be available, as usual, for either playout or
>> record. When not in Key/Fill mode, either file may be played back as
>> a standard clip file.

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