如何在 python 中使用 opencv 处理图像?

how to process image with opencv in python?

我想使用 opencv 库中的边缘检测算法。
这是一段python代码:

1
2
3
4
5
6
7
8
9
10
11
12
13
from opencv.cv import *
from opencv.highgui import *

img = cvLoadImage ('xxx.jpg')
cvNamedWindow ('img')
cvShowImage ('img', img)
cvWaitKey ()

canny = cvCreateImage (cvSize (img.width, img.height), 8, 3)
cvCanny (img, canny, 50, 200)

harris = cvCreateImage (cvSize (img.width, img.height), 8, 3)
cvCornerHarris (img, harris, 5, 5, 0.1)

加载和显示图像工作正常,但 canny 和 harris 转换失败。
cvCanny 失败:

1
2
3
4
5
6
RuntimeError:  openCV Error:
    Status=Unsupported format or combination of formats
    function name=cvCanny
    error message=
    file_name=cv/cvcanny.cpp
    line=72

cvCornerHarris 失败并显示以下错误:

1
2
3
4
5
6
RuntimeError:  openCV Error:
    Status=Assertion failed
    function name=cvCornerHarris
    error message=src.size() == dst.size() && dst.type() == CV_32FC1
    file_name=cv/cvcorner.cpp
    line=370

从这条消息我可以推断加载的图像格式无效。但我不明白如何转换它。
以下是一些 img 字段的值:

1
2
3
img.type = 1111638032
img.nChannels = 3
img.depth = 8


对于对同一类型问题感兴趣的其他人,我建议查看 http://simplecv.org

这是我编写的一些代码,用于对从网络摄像头获取的图像进行线条检测。它甚至会通过 http 显示图像。 beard

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
import SimpleCV
import time

c = SimpleCV.Camera(1)
js = SimpleCV.JpegStreamer()

while(1):
  img = c.getImage()
  img = img.smooth()
  lines = img.findLines(threshold=25,minlinelength=20,maxlinegap=20)
  [line.draw(color=(255,0,0)) for line in lines]
  #find the avg length of the lines
  sum = 0
  for line in lines:
      sum = line.length() + sum
  if sum:
      print sum / len(lines)
  else:
      print"No lines found!"
  img.save(js.framebuffer)
  time.sleep(0.1)

查看我在 http://labs.radiantmachines.com/beard/ 上制作的项目,它会检测你脖子上的胡须有多长:)


这是固定代码。请参阅内联评论。长话短说:你的数据类型是错误的。阅读 API。

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
try:
    from opencv.cv import *
    from opencv.highgui import *
except:
    #
    # Different OpenCV installs name their packages differently.
    #
    from cv import *

if __name__ == '__main__':
    import sys
    #
    # 1 = Force the image to be loaded as RGB
    #
    img = LoadImage (sys.argv[1], 1)
    NamedWindow ('img')
    ShowImage ('img', img)
    WaitKey ()

    #
    # Canny and Harris expect grayscale  (8-bit) input.
    # Convert the image to grayscale.  This is a two-step process:
    #   1.  Convert to 3-channel YCbCr image
    #   2.  Throw away the chroma (Cb, Cr) and keep the luma (Y)
    #
    yuv = CreateImage(GetSize(img), 8, 3)
    gray = CreateImage(GetSize(img), 8, 1)
    CvtColor(img, yuv, CV_BGR2YCrCb)
    Split(yuv, gray, None, None, None)

    canny = CreateImage(GetSize(img), 8, 1)
    Canny(gray, canny, 50, 200)
    NamedWindow ('canny')
    ShowImage ('canny', canny)
    WaitKey()

    #
    # The Harris output must be 32-bit float.
    #
    harris = CreateImage (GetSize(img), IPL_DEPTH_32F, 1)
    CornerHarris(gray, harris, 5, 5, 0.1)


您可以一步而不是两步将图像转换为灰度:

1
2
gray = cv.CreateMat(img.height, img.width, cv.CV_8UC1)
cv.CvtColor(img, gray, cv.CV_BGR2GRAY)