python中PIL.Image，OpenCV，Numpy,str 图像格式相互转换
numpy array
opencv
PIL Image
base64.b64encode
str
# 获取图片的二进制数据
open('x.jpg', 'rb') as g：
bindata = g.read()
binbytes = urllib2.urlopen('http://www.test.com/x.jpg').read()
# binbytes与直接以rb二进制读图片文件获取的数据bindata完全一样,同为字节流,数据类型为str
#io.BytesIO():#Create a buffered I/O implementation using an in-memory bytes
# | buffer, ready for reading and writing.
iobuf = io.BytesIO(bindata) # 二进制字节转换为iobuffer
# iobuffer 对象通过PIL的open函数打开获得PIL图像实例
im = Image.open(iobuf)
#In [300]: im.size
#Out[300]: (480, 640)
mat = np.asarray(im) # 转换PIL的img对象为numpy的array
#In [314]: mat.shape
#Out[314]: (640L, 480L, 3L)
b64bytes = base64.encode(binbytes) # 2进制字节流str经base64编码后str
#In [274]: len(binbytes)
#Out[274]: 95464
#In [279]: len(b64bytes)*3/4 -bda64.count('=',-2) #
#Out[279]: 95464
npa = np.frombuffer(binbytes, np.uint8) # or np.fromstring(bytestr,np.uint8)
#In [295]: npa.shape
#Out[295]: (95464L,)
img = cv2.imdecode(npa, cv2.IMREAD_COLOR)
#In [299]: img.shape
#Out[299]: (640L, 480L, 3L)
imec = cv2.imencode('.jpg', mat)
#In [320]: imec
#Out[320]:
#(True, array([[255],
# [216],
# [255],
# ...,
# [153],
# [255],
# [217]], dtype=uint8))
#In [321]: imec[1].shape
#Out[321]: (63495L, 1L) # imagemat(640L, 480L, 3L)经imencode编码后大小
imec[1].tobytes() # 或imec[1].tostring() 转换mat为字节流#Convert between NumPy 2D array and NumPy matrix
a = numpy.ndarray([2,3])# create 2x3 array
m1 = numpy.asmatrix(a)# does not create new matrix, m1 refers to the same memory as a
m2 = numpy.matrix(a)# creates new matrix and copies content
b1 = numpy.asarray(m2)# does not create array, b1 refers to the same emory as m2
b2 = numpy.array(m2)# creates new array and copies content
Read/Write Images with OpenCV
image = cv.LoadImage(“ponzo.jpg”)
cv.SaveImage(“out.png”, image)
Read/Write Images with PIL
image = Image.open(“ponzo.jpg”)
image.save(“out.jpg”)
Read/Write Images with PyOpenCV
mat = cv2.imread(“ponzo.jpg”)
cv2.imwrite(“out.png”, mat)
#Convert between OpenCV image and PIL image
# color image
cimg = cv.LoadImage("ponzo.jpg", cv.CV_LOAD_IMAGE_COLOR) # cimg is a OpenCV image
pimg = Image.fromstring("RGB", cv.GetSize(cimg), cimg.tostring()) # pimg is a PIL image
cimg2 = cv.CreateImageHeader(pimg.size, cv.IPL_DEPTH_8U, 3)# cimg2 is a OpenCV image
cv.SetData(cimg2, pimg.tostring())
#Note: OpenCV stores color image in BGR format. So, the converted PIL image is also in BGR-format. The standard PIL #image is stored in RGB format.
# gray image
cimg = cv.LoadImage("ponzo.jpg", cv.CV_LOAD_IMAGE_GRAYSCALE)# cimg is a OpenCV image
pimg = Image.fromstring("L", cv.GetSize(cimg), cimg.tostring()) # img is a PIL image
cimg2 = cv.CreateImageHeader(pimg.size, cv.IPL_DEPTH_8U, 1) # img2 is a OpenCV image
cv.SetData(cimg2, pimg.tostring())
Convert between PIL image and NumPy ndarray
image = Image.open(“ponzo.jpg”)# image is a PIL image
array = numpy.array(image) # array is a numpy array
image2 = Image.fromarray(array)# image2 is a PIL image
Convert between PIL image and PyOpenCV matrix
image = Image.open(“ponzo.jpg”)# image is a PIL image
mat = cv2.Mat.from_pil_image(image) # mat is a PyOpenCV matrix
image2 = mat.to_pil_image()# image2 is a PIL image
Convert between OpenCV image and NumPy ndarray
cimg = cv.LoadImage("ponzo.jpg", cv.CV_LOAD_IMAGE_COLOR)# cimg is a OpenCV image
pimg = Image.fromstring("RGB", cv.GetSize(cimg), cimg.tostring()) # pimg is a PIL image
array = numpy.array(pimg) # array is a numpy array
pimg2 = cv.fromarray(array) # pimg2 is a OpenCV image
还可以参考这样形式的代码：
PIL.Image转换成OpenCV格式：
import cv2
from PIL import Image
import numpy
image = Image.open("plane.jpg")
image.show()
img = cv2.cvtColor(numpy.asarray(image),cv2.COLOR_RGB2BGR)
cv2.imshow("OpenCV",img)
cv2.waitKey()
OpenCV转换成PIL.Image格式：
import cv2
from PIL import Image
import numpy
img = cv2.imread("plane.jpg")
cv2.imshow("OpenCV",img)
image = Image.fromarray(cv2.cvtColor(img,cv2.COLOR_BGR2RGB))
image.show()
cv2.waitKey()
#numpy array 转 PIL Image
img = Image.fromarray(img.astype('uint8')).convert('RGB')
# save img
img.save("t.jpg")