.na
.nh
.TH subimstat 1 4.6.34 IMOD
.SH NAME
subimstat - Subtracts one average image from another with a t-test
.SH SYNOPSIS
subimstat
.SH DESCRIPTION
.P
Subimstat subtracts one average image from another and uses standard
deviation or variance images to find the statistical significance of the
difference at each pixel, as evaluated by a t-statistic. It then sets to
zero all differences that are less significant than the specified level of
significance. It can also output pixel values reflecting the level of
significance rather than the difference.
.P
The average and standard deviation/variance images can be ones produced by
Imavgstat, Clip, PEET, or other means. When one starts the program, one
designates a pair of A files (with average and S.D./variance images) and a
pair of B files. One can then subtract any section in B from any section in
A; A and B may be the same pair of files. Alternatively, a whole set of
corresponding sections can be subtracted between the two files.
.P
The user is responsible for keeping track of how many samples were used in
making each average, and informing this program of those numbers. The
program needs these numbers to compute the t-statistic and evaluate its
significance.
.P
Entries to the program:
.P
.nf
Average image file A
Standard deviation or variance image file A
Average image file B, or Return if same as file for A
Standard deviation or variance image file B, or Return if same as file
for A
Output image file to store differences in
.fi
.P
0 if the files have standard deviations in them, or 1 if the files
have variances
.P
0 to enter each pair of sections separately, with potentially different
numbers of samples and significance levels, or 1 to enter a list of
corresponding sections and treat them all the same.
.P
IF you entered 0, next enter:
.P
The number of differences to compute
.P
Then for each difference, enter:
.P
Section # in file A, section # in file B
.P
Number of samples making up those averages in A and B
.P
Significance level for setting differences to zero. Enter a
probability value such as 0.05, 0.01, etc. Differences less
significant than this value will be set to zero. Enter a
negative value to have significant pixels values set to
the negative of the log of the probability, or to the positive
log for negative differences. For example, positive and
negative differences with a P of 0.01 would be output as
2 and -2, respectively.
.P
IF you entered 1 to treat a set of corresponding sections the same, next
enter:
.P
The list of sections to subtract between the files, or / to do all
sections
.P
The number of samples making up the averages in A and B
.P
The significance level for settings differences to zero, a positive
or negative value as just described.
.P
.SH HISTORY
.nf
Written by David Mastronarde, 1/27/90
4/23/90 - have program look up criterion t value.
4/12/95 - use local subroutines for t-value
1/19/11 - allow list of corresponding sections
.fi
.SH BUGS
Email bug reports to mast@colorado.edu.