Question

为什么同一图像的2个矩阵的“步长”值不同？

其中一个是由LoadImageM()生成的，另一个是GetMat()在图片加载LoadImage()后生成的。我的代码是：

import cv2.cv as cv
def main():
    org_win = 'Original'
    cv.NamedWindow(org_win, cv.CV_WINDOW_AUTOSIZE)
    org_img = cv.LoadImage("bed.jpg", cv.CV_LOAD_IMAGE_COLOR)
    cv.ShowImage(org_win, org_img)

    org_img_mat1 = cv.LoadImageM("bed.jpg", cv.CV_LOAD_IMAGE_COLOR)
    org_img_mat2 = cv.GetMat(org_img, 0)

    print org_img_mat1
    print org_img_mat2

    cv.WaitKey(0)
    cv.DestroyWindow(org_win)

if __name__ == '__main__': main()

我得到的结果是：

<cvmat(type=42424010 8UC3 rows=497 cols=681 step=2043 )>
<cvmat(type=42420010 8UC3 rows=497 cols=681 step=2044 )>

步数值导致这种差异的原因是什么？请赐教。

Answer 1

以下是cv.LoadImage和cv.LoadImageM的源代码：

static PyObject *pycvLoadImage(PyObject *self, PyObject *args, PyObject *kw)
{
  const char *keywords[] = { "filename", "iscolor", NULL };
  char *filename;
  int iscolor = CV_LOAD_IMAGE_COLOR;

  if (!PyArg_ParseTupleAndKeywords(args, kw, "s|i", (char**)keywords, &filename, &iscolor))
    return NULL;

  // Inside ALLOW_THREADS, must not reference 'filename' because it might move.
  // So make a local copy 'filename_copy'.
  char filename_copy[2048];
  strncpy(filename_copy, filename, sizeof(filename_copy));

  IplImage *r;
  Py_BEGIN_ALLOW_THREADS
  r = cvLoadImage(filename_copy, iscolor);
  Py_END_ALLOW_THREADS

  if (r == NULL) {
    PyErr_SetFromErrnoWithFilename(PyExc_IOError, filename);
    return NULL;
  } else {
    return FROM_IplImagePTR(r);
  }
}

static PyObject *pycvLoadImageM(PyObject *self, PyObject *args, PyObject *kw)
{
  const char *keywords[] = { "filename", "iscolor", NULL };
  char *filename;
  int iscolor = CV_LOAD_IMAGE_COLOR;

  if (!PyArg_ParseTupleAndKeywords(args, kw, "s|i", (char**)keywords, &filename, &iscolor))
    return NULL;

  // Inside ALLOW_THREADS, must not reference 'filename' because it might move.
  // So make a local copy 'filename_copy'.
  char filename_copy[2048];
  strncpy(filename_copy, filename, sizeof(filename_copy));

  CvMat *r;
  Py_BEGIN_ALLOW_THREADS
  r = cvLoadImageM(filename_copy, iscolor);
  Py_END_ALLOW_THREADS

  if (r == NULL) {
    PyErr_SetFromErrnoWithFilename(PyExc_IOError, filename);
    return NULL;
  } else {
    return FROM_CvMatPTR(r);
  }
}

看起来主要区别在于return FROM_IplImagePTR(r)与return FROM_CvMatPTR(r) step IplImage在CvMat中基于一个索引，但在{{1}}中基于零的索引？

步骤＆＃39;的差异对于OpenCV中相同图像的2个矩阵

1 个答案: