Convert MHA format to PNG image

import skimage.io
import matplotlib.pyplot as plt
import os
 
def mha2png(file_path, dest_dir, slices=None):
 
    if not os.path.exists(dest_dir):
        output_file = dest_dir
        os.mkdir(output_file)
 
    img = skimage.io.imread(fname=file_path, plugin='simpleitk')
 
    if slices == None:
        slice_min = 0
        slice_max = img.shape[0]
    else:
        slice_min = slices[0]
        slice_max = slices[1]
 
    for slicer in range(slice_min,slice_max):
        plt.imsave(dest_dir + '/' + dest_dir + '_' + str(slicer) + '.png', img[slicer], cmap='gray',format='png')
 
if __name__=='__main__':
 
    input_path = ('mha')
    for root, dirs, files in os.walk(input_path):
        for filename in files:
            input_file = os.path.join(root, filename)
            output_path = input_file.replace('.mha','')
            output_path = output_path.replace(input_path,'')
            output_path = output_path.replace('\\','')
            mha2png(input_file, output_path)