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

VFX name:

i3d_Histogram

IMPROMPTU Equivalent:

3d_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 (x,y) represents the number of voxels falling within grayscale bin number x and slice group # y. The y^th 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

levels_per_bin = 1
slices_per_group = 1
starting_slice = 1
smooth_hist = yes
image_out = undefined
second_volume = 0

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

The parameter ``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 $M \times l$ 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+$2\times l$-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.