Convert between Python tuple and list

a = (1, 2)      # a is a tuple
b = list(a)     # b is a list
c = tuple(b)  # c is a tuple

Convert between Python tuple, list and NumPy 1D array

a = (1, 2)          # a is a tuple
b = np.array(a)  # b is an numpy array
c = tuple(b)       # c is a tuple

a = [1, 2]          # a is a python array
b = np.array(a)  # b is a numpy array
c = list(b)          # c is a python list

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 memory as m2
b2 = numpy.array(m2)      # creates new array and copies content
 

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())                 # pimg is a PIL image
cimg2 = cv.CreateImageHeader(pimg.size, cv.IPL_DEPTH_8U, 1)              # cimg2 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 = pyopencv.Mat.from_pil_image(image)  # mat is a PyOpenCV matrix
image2 = mat.to_pil_image()                        # image2 is a PIL image