Can someone explain luminance shift?

M

m_bass

Active member
Could someone explain what luminance shift is. For example last year I cut a Mardi Gras package for WYES in New Orleans, and the engineer there said there was a luminance shift on some of the dissolves. Since I have to do another pkg for them this year I would like to find out what I should be looking for or if he is just being picky. Any help would be greatly appreciated. Mike
 
Luminance shift in video engineering also called luma shift or Y/C delay is caused by the way (component) video signals are being processed and/or transported in digital and analog systems as well. Of course it can be determined in what part(s) of the signal chain the shift originates, but the phenomenon is always the same: on the screen we see the color part of colored objects slightly (mostly horizontally) displaced w.r.t. the black and white part. Sometimes the problem is called "misplaced lips" therefore. Broadcasters can easely correct these Y/C delay problems. Allmost all TBC's have this funtionallity. So the engineer was maybe proud to show his knowledge.
 
Thanks for the reply Andre. I kinda get what your talking about. Is this something that I can see and correct as I’m editing or is it happening during export and transfer to beta? Mike
 
Although some DV Codecs use(d) to introduce Y/C delay problems, most probably if you get it with a recorded Beta playback, it sits in the analog part. Try to verify the analog playback from DV before recording to Beta. Normally a dual beam oscilloscope is needed, but if you shoot a vertical red bar (about 10% of the picture width) on a white or yellow background, Y/C delays can be estimated quite well on playback on a callibrated monitor. To correct you need a TBC with Y/C adjusting function between the DV player output and the Beta input.
 
Now i understand whats going on. Thanks for your help Andre, I guess I need to start looking for a TBC on E-Bay...
 
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