VHS/SVHS Tape Copy High Resolution 
Tape Copy with Minimal Loss

Video tapes lose resolution and intensity when copied.  If copies are made from copies, the loss becomes rather extreme and unacceptable.  In order to minimize the loss of information content in resolution and intensity, the video signal must pass through a full frame time base correction unit (a 525 line TBC) with both color and gray scale intensity adjustments.  Furthermore, the signal path used for the copy process should be the SVHS pathway.  The SVHS pathway is wider bandwidth than the VHS pathway and introduces less signal loss.  Only high quality new video tapes should be used in the copy process.  The resulting copy will be stable, bright, with good contrast, playable in ordinary VCR units.  The copy tape is VHS since the original signal is VHS though on the SVHS pathway.  The copied VHS tape suffers none of the usual loss factors associated with VHS to VHS tape copy.

TREC requests the original incident scene videotape for the Forensic Video Image Analysis.  TREC avoids copy tapes for Forensic Video Image Analysis where the original videotape is available.  Justification for the original incident scene videotape for Forensic Video Image Analysis follows.  As an aspect TREC’s workshops to law enforcement, industrial security, and the courts, tape copy is given very serious attention.  Videotapes from incident scene situations are normally of poor quality.  The videotape copy of the poor quality original video normally results in a poorer quality video, i.e. information is lost in the copy process. 

"Tape Copy Loss S-VHS Study"  

Generation

Original

3rd

5th

Luminance SNR

57.2db

51.7db

49db

Shades of Gray

724

384

281

Percent Loss

 

47%

61.2%

Reference: Peter Utz, NATIA presentation 1992 Panasonic AG 7500A S-VHS VCR, Panasonic Basic Video Guild. Note that the following referenced study is for Super VHS. The results for the more common VHS tapes, a lower resolution are worse. Use of copy tapes for Forensic Video Analysis must be avoided where possible.

This study and report by Peter Utz, Panasonic Corporation, was presented at the 1992 NATIA (National Technical Investigators Association) workshop. (NATIA is the national organization for sworn technical service officers through out the nation.)  The study documents the loss of information from the tape copy process.  Forensic Video Image Analysis can ill afford to lose information that might be pertinent to a incident, i.e. perpetrator identification, recognition of a unique feature, license plate alphanumeric, etc.  Therefore, every effort must be put forth to obtain the original incident scene videotape for Forensic Video Image Analysis.  That effort includes, where necessary, filing a motion before the Court requesting the production of the original incident scene videotape from the custodian of the data.

 

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