Re: [AMIA-L] Digital to analog glitch?

[David Crosthwait <DCFWTX@AOL.COM>]

In a message dated 7/18/02 7:07:43 AM Pacific Daylight Time,
jenemann@EARTHLINK.NET writes:

<< We have a digital to analog problem, and aren't quite sure how to deal
 with it.  Simply put, our commercial has a second of digital breakup in
 it.

 The glitch: After a product shot that is basically red and yellow (pizza, to
 be exact) , a little boy takes a bite of the pizza (more colors) and there
 is a second of breakup.

 This breakup occurs in every version of the commercial, and therefore
 we know the problem is not without Digibeta master but with the spot
 itself. The editors noticed this glitch on their plasma screen, and I'm
 noticing it on a regular monitor with a 3/4" tape that's come from a
 Digibeta master.  However, viewed on other screens or with the
 Digibeta master, everything has been fine.

 As the consumer end of the advertising world is still a 3/4" and 1/2"
 one, this is going to be a problem.  Any advice?
  >>

Your problem may be excessive chroma levels (assuming that the video peaks
are not exceeding 100 I. R. E.) which certain monitors can't handle. In the
broadcast world, it's referred to as "illegal chroma levels". Can this scene
be viewed on a calibrated waveform monitor, or vectorscope? If so, chroma
flat peaks generally should be kept less than 120 units maximum on a waveform
monitor, and not exceeding the outer vector ring on a vectorscope. If chroma
does exceed these values, video tearing may occur. This excessive level may
also be grounds for technical rejection by broadcast entities. Broadcast
transmitters don't like excessive video and chroma levels. Therefore, rigid
standards are imposed by television broadcasters and post production
facilities to minimize video problems such as these. Often, a chroma clipper
can reduce or eliminate these artifacts by reducing chroma peaks, thereby
rendering a more "legal" chroma level, with barely visible changes in the
chroma values of the offending scene.

It is always in the best interest of the producer or editor to not have their
product produce any negative video effects on any monitor in the production
facility, assuming that all viewing monitors and VCRs are working in a
somewhat normal or calibrated state. In post production circles, we normally
tweak video for "worse case scenarios," taking into account on what and where
the video product could possibly be viewed on. No one likes a rejected tape
coming back to a facility.

Regards,

David C. Crosthwait
President, DC Video
177 West Magnolia Blvd.
Burbank, CA. 91502
818-563-1073
818-563-1177 (fax)

Email: DCFWTX@AOL.COM