图像阈值
ret, dst = cv2.threshold(src, thresh, maxval, type)
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src： 输入图，只能输入单通道图像，通常来说为灰度图
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dst： 输出图
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thresh： 阈值
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maxval： 当像素值超过了阈值（或者小于阈值，根据type来决定），所赋予的值
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type：二值化操作的类型，包含以下5种类型： cv2.THRESH_BINARY； cv2.THRESH_BINARY_INV； cv2.THRESH_TRUNC； cv2.THRESH_TOZERO；cv2.THRESH_TOZERO_INV
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cv2.THRESH_BINARY 超过阈值部分取maxval（最大值），否则取0
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cv2.THRESH_BINARY_INV THRESH_BINARY的反转
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cv2.THRESH_TRUNC 大于阈值部分设为阈值，否则不变
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cv2.THRESH_TOZERO 大于阈值部分不改变，否则设为0
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cv2.THRESH_TOZERO_INV THRESH_TOZERO的反转
# 先将图片转化为灰度图
img = cv2.imread('cat.jpg')
img_gray = cv2.cvtColor(img,cv2.COLOR_BGR2GRAY)
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)
# 展示图片
titles = ['Gray Image', 'BINARY', 'BINARY_INV', 'TRUNC', 'TOZERO', 'TOZERO_INV']
images = [img, 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()
结果为：