Topic:
What is the best way to set the gain control for seismic display?

Description:
        

Solution:
Seismic Display > Define > Display spec > Gain control

There are 5 options under 'Type'.

RMS     - Will take the RMS value of the 'source' as the 'Reference Values' (RV)
mean    - Will take the mean value of the 'source' as the 'Reference Values'     
          (RV)
max     - Will take the max value of the 'source' as the 'Reference Values' (RV)
min/max - Will take the min and max values of the 'source' as the 'Reference     
          Values' (RV) .Note: With this option the spectrum will not usually be  
          balanced (ie 0.0 will not be the center of the spectrum),user may      
          want to edit zero reference.
user    - Will take values entered by the user in User Min and User Max as the   
          'Reference Values' (RV).If spectrum is not balanced user may want to   
          change zero reference.

There are 4 options under 'Source'.

Trace   -  RV's will be calculated for each trace and scaled on a trace by trace 
           basis.
           Note: This is the only option available for use with Type = User.
Line    -  RV's will be calculated for the displayed line and the whole line     
           scaled using these values.
Survey  -  RV's will be calculated using all data in the current survey and each 
           line displayed from this survey will be scaled using these values.
Class   -  RV's will be calculated using all data in the current class and each  
           line displayed from this class will be scaled using these values.


Amplitude - This is the value at which the RV is placed on the spectrum.
            eg. If Amplitude is set to 100 the RV will be placed 1/4 of the      
                distance from the center of the colour spectrum.
            
                If Amplitude is set to 200 the RV will be placed 1/2 of the      
                distance from the center of the colour spectrum.
                
                If Amplitude is set to 300 the RV will be placed 1/3 of the      
                distance from the center of the colour spectrum.
                
                If Amplitude is set to 400 the RV will be placed at the ends  of 
                the colour spectrum.
                
Zero Reference - The value at the center of the spectrum.

User Min/User Max - Only used for input when type is set to 'User'
                    (Note: Although values can be typed in here at any time they   
                     will only be used in conjunction with type 'User')    
                    
Polarity - For display purposes only.
           Interpretation will be done at the polarity specified when data is     
           loaded.Snap and extract commands do not recognize the Reverse         
           Polarity option.                                
                
                
With these factors in mind we would suggest the following settings for 'normal' 
displays.

When using Type = RMS or mean       Source = Any        Amplitude value = 120
This will position the RV's just over 1/4 of the distance from the center of 
the spectrum.
Zero Reference = 0.0
Zero will be in the center of the balanced spectrum.


When using Type = max               Source = Any        Amplitude value = 400
This will position the RV's at each end of the spectrum.
If we use Amplitude = 100 only 1/4 of the color spectrum would be used.
The RV's would be placed at 1/4 of the distance from the center of the spectrum
and as max values are definitive no other values would be using the rest of the 
spectrum.
Zero Reference = 0.0
Zero will be in the center of the balanced spectrum.


When using Type = min/max or user  Source = Any         Amplitude value = 400
(Note: Type=User,Source=Trace)

This will position the RV's at each end of the spectrum.
If we use Amplitude = 100 only 1/4 of the color spectrum would be used.
The RV's would be placed at 1/4 of the distance from the center of the spectrum
and as min max values are definitive no other values would be using the rest of 
the spectrum. 
Zero Reference = 0.0 or userdefined to balance spectrum.
Zero will not always be in the center of the spectrum.

The user option can be made very flexible for the display of different data 
types eg porosity and coherency.





Last Modified on: 04-NOV-98