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AS AD - Add to an existing average - find variance.

(8/22/96)

PURPOSE

Adds 2 or more (up to 500) pictures together, computing several measures of variance (per point, total, etc.). The sum and the variance image are stored in separate output files. Images are to be added to the existing average and variance file. See warning in operation 'AS'

SEE ALSO

AS [Average images - find & save variance]
AS DC [Average images - find & save variance, doc. file]
AS F [Average images - find statistics & Q factor map]
AS R [Average images - find & save variance, better]

USAGE

.OPERATION: AS AD X10
[On input the register has to contain the value of the average offset of existing average file. On output it is to receive the value of the new average offset.]

FOR IMAGES TO BE AVERAGED
.ENTER 3 LETTER FILE PREFIX OR TEMPLATE (EG. PIC****): PIC
[Enter prefix of images to be added.]

.ENTER FILE NUMBERS: 1-10,12,15-17
[Enter numbers of files within a series to be added.]

.ALL, ODD-EVEN (A/O): O
['A' - all images will be added, 'O' - two subaverages will be calculated: one for odd-numbered images and one for even-numbered images. The next two questions will appear twice.]

.AVERAGE FILE: AVG001
[Enter name of output file receiving average.]

.ENTER NO. OF IMAGES ALREADY AVERAGED: 14
[Enter number of files originally averaged. This number will be used as an offset in its computations.]

.VARIANCE FILE: VAR001
[Enter name of output file receiving variance map.]

[Questions for average file, number of images already averaged and variance file are repeated if option O-E was chosen.]

The following values are then printed out:

 
          Number of images 
          Number of elements 
          Total variance         Total std. deviation 
          Variance per point     Std. deviation per point 
          Average offset 
          Variance of average image 

NOTES

  1. The average file will be normalized so that its mean pixel value (X5) is equal to 0. To "restore" MIN and MAX values comparable to those of the input files, use 'AR'. For example, if the average offset was 0.00131, you would have ((P1*0.00131)+0.), with P1 as the input average file. This is important if you intend to contour the average using 'FC', since negative values in the file will give a nonsense result.

  2. If you calculate an average in more than one step, each average-offset is independent. To get the correct average offset of the complete image, the average of the subaverage average-offsets has to be used.

  3. If the old offset in register is not given, a warning is printed and the operation is terminated.

SUBROUTINES

ADDS

CALLER

UTIL2

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