Grass Valley PVS Series System Guide v.4.0 Dec 10 200 - Manual (Page 119)

Guidelines for selecting Video Quality Presets
July 27, 2001 Profile XP System Guide 119
data rates to maintain quality.
-Higher data rates should be used for any production work that requires multiple
generations or when the material is subject to up-conversion to HDTV.
NOTE: Information about Profile XP system storage capacities for different video
data rates is located in Chapter 3, “Working with Profile XP storage systems” on
page 58.
• Chrominance Sampling Method - Options include 4:2:2 and 4:2:0. Consider
the following guidelines:
-Select 4:2:2 encoding whenever storage capacity allows it, especially when you
know the video is subject to up-conversion to HDTV or is being used in a
production environment where it will experience multiple generations.
-For video not subject to up-conversion or multiple generations, 4:2:0 sampling
can be used for slightly better picture quality below 10Mb/s since the
reduction in chrominance information allows more detail in the luminance
information. However, reducing chrominance information by half does
impact picture quality in a video sequence with large chrominance variance.
• GOP Length - Determines the number and structure of I, P, and B frames. Since
B frames contain 25% of the information of an I frame and a P frame contains
about 50%, significant storage efficiencies can be realized with long GOP
structures. In general then, lengthening the GOP structure allows operation at
lower data rates for equivalent picture quality. Consider the following
guidelines:
-Choose the longest GOP structure possible as the storage benefits outweigh the
picture quality improvements.
-Use I frame only and short GOP structures for editing applications which need
flexibility in performing insert edits.
-Use I frame only for off speed play.