python - 在 python 中更改 CvSeq 中的元素

Question

我正在尝试从图像中提取轮廓，旋转这些轮廓并将它们插入到新图像中。代码如下。我的问题出在旋转轮廓方法中。执行代码时会看到以下错误“TypeError:‘cv.cvseq’对象不支持项目分配”。

关于如何解决这个问题的任何想法？我正在为 Opencv 2.2 使用 python 绑定(bind)。

import cv

def rotateContour(contour, centerOfMass, angle):
    for index in range(0, len(contour)):
        contour[index] = rotatePoint(contour[index], centerOfMass, angle)   
    return contour

def rotatePoint(point, centerOfMass, angle):
    px, py = point
    x, y = centerOfMass
    temppoint = (px-x, py-y)
    temppointx = temppoint[0]*math.cos(angle) + temppoint[1] * math.sin(angle)
    temppointy = temppoint[1]*math.cos(angle) - temppoint[0] * math.sin(angle)
    temppoint = (temppointx + x, temppointy + y)

    return temppoint

inputimage = cv.LoadImage('filename.png', cv.CV_LOAD_IMAGE_GRAYSCALE)
outputimage = cv.CreateImage((10000, 300), 8, 1)

storage = cv.CreateMemStorage (0)
contours = cv.FindContours(inputimage, storage, cv.CV_RETR_EXTERNAL, cv.CV_CHAIN_APPROX_SIMPLE)

for contour in contour_iterator(contours):
    gray = cv.CV_RGB(200, 200, 200)
    # Rotate contour somehow
    contour = rotatecontour(contour)
    cv.DrawContours(outputimage, contour, gray, gray, 0, -1, 8)

cv.SaveImage("outputfile.png", outputimage)

Answer 1

似乎您无法使用 Python 绑定(bind)更改 cvseq 对象的元素(注意 here 仅用于操作 cvseq 对象的 Python 方法列表具有删除序列元素和更改其顺序的方法。)

尽管如此，Python 绑定(bind)确实提供了实现旋转图像轮廓的既定目标的工具。

由于 cv.DrawContours() 方法需要一个 cvseq 作为输入，我们必须在 Python 中存储和操作之后找到其他绘制轮廓的方法。一种方法是使用 cv.FillPoly() 或 cv.DrawPoly() 方法(将元组列表的列表作为输入)，具体取决于传递给 cv.DrawContours() 的厚度参数分别为 -1 或 > 0。

因此，找到轮廓并绘制其旋转对应物的一种方法如下(通过以填充形式重新绘制并使用 OpenCV 的力矩函数找到每个轮廓的质心):

import cv
import numpy as np

# Draw contour from list of tuples.
def draw_contour( im , contour , color , thickness = 1 , linetype = 8 ,
                  shift = 0 ) :
  if thickness == -1 :
    cv.FillPoly( im , [contour] , color , linetype , shift )
  else :
    cv.PolyLine( im , [contour] , True , color , thickness , linetype , shift )

# Rotate contour around centre point using numpy.
def rotate_contour( contour , centre_point , theta ) :
  rotation = np.array( [ [ np.cos( theta ) , -np.sin( theta ) ] , 
                         [ np.sin( theta ) ,  np.cos( theta ) ] ] )
  centre = np.vstack( [ centre_point ] * len( contour ) )
  contour = np.vstack( contour ) - centre
  contour = np.dot( contour , rotation ) + centre
  return [ tuple ( each_row ) for each_row in contour ]

# Find centre of mass by drawing contour in closed form and using moments.
def find_centre_of_mass( contour ) :
  bottom_right = np.max( contour , axis = 0 )
  blank = cv.CreateImage( tuple ( bottom_right ) , 8 , 1 )
  cv.Set( blank , 0 )
  draw_contour( blank , contour , 1, -1 )
  moments = cv.Moments( blank , 1 )  
  sM00 = float ( cv.GetSpatialMoment( moments , 0 , 0 ) )
  sM01 = float ( cv.GetSpatialMoment( moments , 0 , 1 ) )
  sM10 = float ( cv.GetSpatialMoment( moments , 1 , 0 ) )
  return ( sM10 / sM00 , sM01 / sM00 )

THETA = np.pi / 3.0
COLOR = cv.CV_RGB( 200 , 200 , 200 )
input_image = cv.LoadImage( ‘filename.png’ , cv.CV_LOAD_IMAGE_GRAYSCALE )
output_image = cv.CreateImage( ( input_image.width , input_image.height ) , 
                                 input_image.depth , input_image.nChannels )
cv.Set( output_image , 0 )

storage = cv.CreateMemStorage( 0 )
contour_pointer = cv.FindContours( input_image , storage , 
                                   cv.CV_RETR_EXTERNAL , 
                                   cv.CV_CHAIN_APPROX_SIMPLE )

while contour_pointer is not None :
  contour = contour_pointer [ : ]
  centre_of_mass = find_centre_of_mass( contour )
  rotated_contour = rotate_contour( contour , centre_of_mass , THETA )
  draw_contour( output_image , rotated_contour , COLOR , -1 )
  contour_pointer = contour_pointer.h_next()

cv.SaveImage( ‘outputfile.png’ , output_image)