关于opencv中 THRESH_TRUNC 参数的疑惑

在opencv的阈值处理中，有个截断阈值的参数 THRESH_TRUNC 让我有些疑惑。因为从官方资料解释来看，是大于阈值会被设为阈值，小于阈值的保持不变

（DSTI = (SRCI > thresh) ? THRESH : SRCI），且官方解释截图也是如此：

 Python版代码如下：

import cv2
img_gray = cv2.imread("cat.jpg", cv2.IMREAD_GRAYSCALE) 

import matplotlib.pyplot as plt
ret, thresh1 = cv2.threshold(img_gray, 127, 255, cv2.THRESH_BINARY) 
ret, thresh2 = cv2.threshold(img_gray, 127, 255, cv2.THRESH_BINARY_INV) 
ret, thresh3 = cv2.threshold(img_gray, 127, 255, cv2.THRESH_TRUNC)  
ret, thresh4 = cv2.threshold(img_gray, 127, 255, cv2.THRESH_TOZERO) 
ret, thresh5 = cv2.threshold(img_gray, 127, 255, cv2.THRESH_TOZERO_INV)

titles = ['Original Image', 'BINARY', 'BINARY_INV', 'TRUNC', 'TOZERO', 'TOZERO_INV']
images = [img_gray, thresh1, thresh2, thresh3, thresh4, thresh5] 
for i in range(6):
    plt.subplot(2, 3, i+1), plt.imshow(images[i], 'gray')
    plt.title(titles[i])
    plt.xticks([]), plt.yticks([])
plt.show() 

得到图像对比结果：

 奇怪的是，TUNC图中，小于阈值127的没有问题，但高于阈值的并非保持127，却变成了最大值255（可取值验证），如果是保持127，图片高光部分应该都是灰色的。这到底是怎么回事呢？

标签：gray,plt,img,cv2,opencv,THRESH,127,TRUNC
来源： https://www.cnblogs.com/baoql/p/15993204.html