AS AD - Average images - add to an existing average

PURPOSE

Adds 2 or more files, computing several measures of variance (per point, total, etc.). The sum and the variance images are stored in separate output files. The command works for, 2D, 3D, real or complex data. WARNING: Use 'AS R' if you want a better variance measure. Use of this command for variances is no longer recommended!

SEE ALSO

AS	[Average images - find variance]
AS R	[Average images - find & save variance, better]
AD S	[Add Series of images]

USAGE

.OPERATION: AS AD [avgoff]

[On input the register variable has to contain the value of the average offset of existing average file. On output it receives 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 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.
   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.
   

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

3. This version of 'AS' does subtracts the average from each image during the calculation of global average and variance. Thus, it results in the variance estimator which is usually far 'too optimistic' - the variance obtained is too small and cannot be used for statistical tests. Use 'AS R'. instead.

SUBROUTINES

ADDS

CALLER

UTIL2