Differences

This shows you the differences between two versions of the page.

--- jvs:cigal:manual:chapter3:analyze [2011/03/31 14:49]
127.0.0.1 external edit
+++ jvs:cigal:manual:chapter3:analyze [2023/02/23 18:43]
@@ Line 1: / Line 1: @@
-**CIGAL Reference Manual, Chapter 3 (Functions): analyze**
-===== Analyze -- Calculate the frequency distribution of values within a variable =====
-**usage: resultarray = analyze(ivarb)**
-ANALYZE reads the input variable, IVARB, and creates an output array where the
-values of the array elements represent a frequency histogram of the values of
-elements in IVARB.  The output array is of LONG type (see [[jvs:cigal:manual:chapter1:variables|VARIABLES(1)]]). The
-elements in the array represent the frequency distribution of the possible
-values in the input.  Thus, element 45 in the output array corresponds to the
-number of elements in the input array with value equal to 45.  For inputs greater
-than 8-bits, only the low-order 12 bits are considered.
-The array produced by ANALYZE is useful for measuring various descriptive properties
-of the input variable.  For example, it can be used to determine the optimal contrast
-enhancement to perform for a given image matrix, or as a way of computing the average
-value of the input.
-Some image processing hardware is capable of performing an ANALYZE operation on an
-entire image at the hardware's video refresh rate.  If the hardware is capable of
-this, and you run ANALYZE on an appropriate hardware image variable, then CIGAL
-automatically lets the hardware perform the computation.  Otherwise, the software
-will do the work, but it may be a bit slow for very large variables.
-As an example, if you have a byte matrix called VGA0, which contains a 320x184 image
-with pixel values covering the middle of the 0-255 intensity range, then the command:
-               buf = analyze(vga0)
-might produce the following array BUF:
-    0    0    0    0    0    0   0    0    0    0    0    0    0    0
-    0    0    0    0    0    0   0    0    0    0    1   33   65   74
-   61   74   62   97   97   92  98  132  120  164  121  192  220  204
-  294  389  421  461  545  673 628  815  691  971 1022  988 1086 1257
-1006 1171 1321  901 1084 1042 891 1133  962  949 1025 1042 1165 1038
-1084 1245  928  960 1066 1052 786  953  855  731  762  831  842  887
-  828  777  879  761  891  687 690  631  664  560  502  534  464  487
-  692  683  681  729  738  490 447  341  220  147  145  130   80   85
-   40   52   18   29   11   10   9    2    2    1    0    0    0    0
-    0    0    0    0    0    0   0    0    0    0    0    0    0    0
-    0    0    0    0    0    0   0    0    0    0    0    0    0    0
-    0    0    0    0    0    0   0    0    0    0    0    0    0    0
-    0    0    0    0    0    0   0    0    0    0    0    0    0    0
-    0    0    0    0    0    0   0    0    0    0    0    0    0    0
-    0    0    0    0    0    0   0    0    0    0    0    0    0    0
-    0    0    0    0    0    0   0    0    0    0    0    0    0    0
-    0    0    0    0    0    0   0    0    0    0    0    0    0    0   0
-The command STATS could then be used to describe BUF as:
-          stats buf
-which tells you that the intensities in VGA0 range from 26 to 130 with the
-greatest number of pixels (1321) at intensity 63.
-The mean pixel value can be quickly calculated from the ANALYZE array as:
-          a = sum(buf)            ; total number of pixels in VGA0
-          buf = buf * ramp(256)   ; weight each intensity by its num. of pixels
-          sum(buf)/a              ; the mean pixel intensity
-The command MEAN(VGA0) would give the same result, but is generally slower.
-**See Also:**\\
-[[jvs:cigal:manual:chapter3:bin|BIN(3)]],
-[[jvs:cigal:manual:chapter1:iproc|IPROC(1)]],
-[[jvs:cigal:manual:chapter3:stats|STATS(3)]],
-[[jvs:cigal:manual:chapter1:variables|VARIABLES(1)]]
-[[jvs:cigal|CIGAL Home]],
-[[jvs:cigal:manual|CIGAL Manual]],
-[[jvs:cigal:manual:chapter3|Functions List]],
-[[jvs:cigal:manual:help|Manual Help]]

Brain Imaging & Analysis Center

User Tools

Site Tools

Differences

Page Tools