Topic:
Seismic data exhibits a banded/striped appearance when displayed

Description:
Newly loaded 3D seismic displayed in VI mode shows that the data
exhibits a banded or striped appearance.  The display accurately
represents a spatial variation of amplitude (more apparent in VA mode).
A look at the amplitude readout (shift+mb1 on a seismic trace) 
shows that amplitudes along horizons are fairly uniform 
until crossing a "band" boundary, at which point the 
amplitude values change by a factor of two.
The data that was loaded was output from the ProMax processing sytem in 
IBM 16 bit integer format.  ProMax uses a scaling algorithm intended to
preserve the full dynamic range of its internal 32 bit floating point 
amplitude values. The ouput module determines the maximum amplitude on the
trace, determines a scale factor (powers of two) that permits the max 
sample to be written as 16 bit integer (preserving its dynamic range),
scales the trace, and stores the scalar in bytes 169-170 of the output SEGY
trace header.

Other processing systems handle data compression on output in a similar fashion.

Solution:
IESX does not perform spatially variant descaling of input 
data.  A single, user defined amplitude scalar may be applied 
to data as it is loaded: (Session Manager > DataManager >
 Load Seismic > Define input format > Scale factor) 

Recreate the SEGY data scaled with a single value by either 
disabling the scaling portion of the compression algorithm or
choosing a format (e.g., 32 bit float) that does not require 
compression (this must be done outside of IESX).  Load this 
SEGY data into IESX.




Last Modified on: 11-AUG-98