Python 2値化済み画像から粒子層の厚みを計測する

import cv2
import matplotlib.pyplot as plt
import numpy as np
from skimage import morphology
from skimage.measure import label
from skimage.morphology import disk, opening

# pathを設定
path = './pic/sample_gray.png'
  
# モノクロ画像として読み込み
img_gray = cv2.imread(path,cv2.IMREAD_GRAYSCALE)
img_gray = img_gray==255

# 型を確認
print(f'type: {type(img_gray)}')

# 次元を確認
print(f'shape: {img_gray.shape}')
  
# 読み込んだ画像を表示
plt.imshow(img_gray,cmap=plt.cm.gray)
plt.show()

# 1の処理
def calc_length(img_gray):
    upper_list=[]
    lower_list=[]
    length_list=[]
    for i in range(img_gray.shape[1]):
        particle_index = np.where(img_gray[:,i]==False)[0]
        upper_list.append(particle_index.min())
        lower_list.append(particle_index.max())
        length_list.append(particle_index.max() - particle_index.min())
    return upper_list,lower_list,length_list

# 2の処理
def process_2(img_gray, th=10000):
    return morphology.remove_small_holes(img_gray, area_threshold=th)

# 3の処理
def process_3(img_gray):
    label_image=label(img_gray==False, connectivity=1)

    max_label=1
    max_area=0
    for i in range(1,label_image.max()+1):
        area=(label_image==i).sum()
        if max_area<area:
            max_label=i
            max_area=area

    return label_image!=max_label

# 4の処理
def process_4(img_gray,radius=20):
    footprint = disk(radius=radius)
    opened = opening(img_gray, footprint)
    return opened

# 結果の出力
def plot_result(upper, lower, length):
    print(f'mean:\t{np.mean(length):.1f}')
    print(f'median:\t{np.median(length):.1f}')
    print(f'std:\t{np.std(length):.1f}')
    plt.imshow(img_gray,cmap=plt.cm.gray)
    plt.plot(range(img_gray.shape[1]),upper,c='red', lw=4)
    plt.plot(range(img_gray.shape[1]),lower,c='red', lw=4)
    plt.show()

    plt.hist(length)
    plt.ylabel('num')
    plt.xlabel('length')
    plt.show()

# 検討案1
upper_1, lower_1, length_1=calc_length(img_gray)

print('検討案1')
plot_result(upper_1, lower_1, length_1)

# 検討案2
img_2 = process_2(img_gray)
upper_2, lower_2, length_2=calc_length(img_2)

print('検討案2')
plot_result(upper_2, lower_2, length_2)

# 検討案3
img_3 = process_3(img_gray)
upper_3, lower_3, length_3=calc_length(img_3)

print('検討案3')
plot_result(upper_3, lower_3, length_3)

# 検討案4
img_4_tmp = process_4(img_gray)
img_4 = process_3(img_4_tmp)
upper_4, lower_4, length_4=calc_length(img_4)

print('検討案4')
plot_result(upper_4, lower_4, length_4)