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图像处理经常需要提取图片的ROI，本文使用Python提取图片的ROI。
使用的Module是PIL (Pillow)，一个图像处理库，用到的函数为类 Image 中的 crop 方法。
函数原型为：
Image.crop(box=None) Returns a rectangular region from this image. The box is a 4-tuple defining the left, upper, right, and lower pixel coordinate. This is a lazy operation. Changes to the source image may or may not be reflected in the cropped image. To break the connection, call the load() method on the cropped copy. Parameters: box – The crop rectangle, as a (left, upper, right, lower)-tuple. Return type: Image Returns: An Image object.
知道矩形的左上角的坐标和右下角的坐标，即可构造box，例如下面的代码
box = (100, 100, 400, 400)
region = im.crop(box)
知道如何提取除ROI时，上面例子为 region，保存ROI到图像则使用类 Image 的 save 方法
region.save(filename)
给出一个Demo，使用人脸数据库GENKI部分的图像做实验，该数据的数字子集GENKI-SZSL提供人脸区域的坐标和大小。提取代码提供如下
from PIL import Image import os src = ‘.‘ imlist = open(src + ‘/GENKI-SZSL_Images.txt‘, ‘r‘).readlines() rs = [float(line.split()[1]) for line in open(src + ‘/GENKI-SZSL_labels.txt‘, ‘r‘).readlines()] cs = [float(line.split()[0]) for line in open(src + ‘/GENKI-SZSL_labels.txt‘, ‘r‘).readlines()] ss = [float(line.split()[2]) for line in open(src + ‘/GENKI-SZSL_labels.txt‘, ‘r‘).readlines()] for i in range(0, len(rs)): path = src + ‘/images/‘ + imlist[i].strip() filename = src + ‘/output/‘ + imlist[i].strip() try: im = Image.open(path) except: continue r = rs[i] c = cs[i] s = ss[i] xLeft = int(c - s/2) yUpper = int(r - s/2) xRight = int(c + s/2) yLower = int(r + s/2) region = im.crop((xLeft, yUpper, xRight, yLower)) region.save(filename)
代码打包下载：http://pan.baidu.com/s/1dD4opKP 密码：ygu7
Pillow的项目文档地址： http://pillow.readthedocs.org
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原文地址：http://www.cnblogs.com/cpointer/p/4899800.html
