``3-D histogram'' -- compute a 3-D histogram

purpose:

Compute a 3-D histogram with the following axes:

x-axis:

grayscale bin number

y-axis:

slice-group number

z-axis:

# of voxels falling in grayscale bin and slice group no.

 

The output is an 8-bit one-slice volume image. The value of a voxel at represents the number of voxels falling within grayscale bin number x and slice group # y. The row of the output image gives the standard grayscale histogram for slices in slice group y.

input:

An 8-bit grayscale volume.

output:

A one-slice 8-bit grayscale volume that represents the 3-D histogram.

parameters:

Default parameters menu is

# of graylevels / histogram bin = 2
* # of slices per group = 2
* starting slice = 1
* smooth histogram = yes
* input from vol # = 0
* second volume = 0
*

The parameter ``# of graylevels / histogram bin = '' gives the number of graylevels assigned to each grayscale bin.

The parameter ``# of slices per group = '' gives the number of volume slices contained in each slice group. The parameter ``starting slice = '' tells the function at which slice to start computing the histogram. As an example, suppose a volume has slices. If we have each slice group contain M slices and start the analysis on the fifth slice, then the y = 0 bin contains the graylevel histogram for slices 5 through 5+l-1, the y=1 slice group contains the graylevel histogram for slices 5+l through 5+-1, etc.

The ``smooth histogram = '' option allows one to apply a light local smoothing (a 5-point Hamming window [22]) to each row of the histogram.

comments:

 

1. I recommend always using the smoothing option. It makes real peaks more definite and makes the histogram much cleaner.
2. I also recommend generally using more than one graylevel per histogram bin -- the histogram again tends to be smoother and fuller.
3. This operation requires moderate computation.