unique_value_counts.py

import SimpleITK as sitk
import numpy as np
import pandas as pd

# downloaded from http://download.alleninstitute.org/informatics-archive/current-release/mouse_ccf/annotation/ccf_2017/
filename = 'annotation_25.nrrd'
itkimage = sitk.ReadImage(filename)
print(itkimage)

numpyImage = sitk.GetArrayFromImage(itkimage)

values, counts = np.unique(numpyImage[:], return_counts=True)
df = pd.DataFrame()

for x in range(len(values)) :

    rec = {}
    rec['count'] = counts[x]
    rec['value'] = values[x]
    df = df.append(rec, ignore_index= True )
    
    
df['value'] = df['value'].astype(np.int)
df['count'] = df['count'].astype(np.int)
    
filename = 'value_count.csv'
df.to_csv( filename, index=False )

Open annotation_25.nrrd file using SimpleITK and count the number of unique values