python 图像处理

cv2.threshold介绍，如下图所示，每个数字代表起本身的灰度值大小

cv2.threshod接收５种类参数形式，分别是cv2.THRESH_BINARY，cv2.THRESH_BINARY_INV，cv2.THRESH_TRUNC ，cv2.THRESH_TOZERO,cv2.THRESH_TOZERO_INV

(1)THRESH_BINARY(Binary Thresholding)

# Binary Threshold,原图像素＞阈值，该像素点的值保持不变，否则为０．即大于阈值的部分变成像素最大值，小于阈值的部分变为０
if src(x,y) > thresh
  dst(x,y) = maxValue
else
  dst(x,y) = 0

(2)THRESH_BINARY_INV(Inverse Binary Thresholding)

# Inverse Binary Threshold，原图像素＜阈值，该像素点的值为０，否则保持不变．与（１）相反，大于阈值的部分变为０，小于阈值的部分变成像素最大值
if src(x,y) > thresh
  dst(x,y) = 0
else
  dst(x,y) = maxValue

(3)THRESH_TRUNC(Truncate Thresholding)

# Truncate Threshold，原图像素＞阈值，该像素点的值等于阈值，否则保持不变．即，将所有像素变成阈值以下水平
if src(x,y) > thresh
  dst(x,y) = thresh
else
  dst(x,y) = src(x,y)

(4)THRESH_TOZERO(Threshold to Zero)

# Threshold to Zero
if src(x,y) > thresh
  dst(x,y) = src(x,y)
else
  dst(x,y) = 0

(5)THRESH_TOZERO_INV(Inverted Threshold to Zero)

# Inverted Threshold to Zero
if src(x,y) > thresh
  dst(x,y) = 0
else
  dst(x,y) = src(x,y)

以上图为例，python代码为：

‘‘‘
    OpenCV Threshold Example
  Copyright 2015 by Satya Mallick <[email protected]>
‘‘‘
# import opencv
import cv2 

# Read image
src = cv2.imread("threshold.png", cv2.IMREAD_GRAYSCALE); 

# Basic threhold example
th, dst = cv2.threshold(src, 0, 255, cv2.THRESH_BINARY);
cv2.imwrite("opencv-threshold-example.jpg", dst); 

# Thresholding with maxValue set to 128
th, dst = cv2.threshold(src, 0, 128, cv2.THRESH_BINARY);
cv2.imwrite("opencv-thresh-binary-maxval.jpg", dst); 

# Thresholding with threshold value set 127
th, dst = cv2.threshold(src,127,255, cv2.THRESH_BINARY);
cv2.imwrite("opencv-thresh-binary.jpg", dst); 

# Thresholding using THRESH_BINARY_INV
th, dst = cv2.threshold(src,127,255, cv2.THRESH_BINARY_INV);
cv2.imwrite("opencv-thresh-binary-inv.jpg", dst); 

# Thresholding using THRESH_TRUNC
th, dst = cv2.threshold(src,127,255, cv2.THRESH_TRUNC);
cv2.imwrite("opencv-thresh-trunc.jpg", dst); 

# Thresholding using THRESH_TOZERO
th, dst = cv2.threshold(src,127,255, cv2.THRESH_TOZERO);
cv2.imwrite("opencv-thresh-tozero.jpg", dst); 

# Thresholding using THRESH_TOZERO_INV
th, dst = cv2.threshold(src,127,255, cv2.THRESH_TOZERO_INV);
cv2.imwrite("opencv-thresh-to-zero-inv.jpg", dst); 

结果图：

(1)                                                           (2)                                                          (3)

(4)                                                                (5)
参考连接：

http://www.learnopencv.com/opencv-threshold-python-cpp/

http://docs.opencv.org/trunk/d7/d4d/tutorial_py_thresholding.html