Some problems with old OpenCV library and haarcascade

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1

Hi to all,
I’m trying to run face recognition on an old version of the OpenCV library, but when uploading a file haarcascade_frontalface_alt.xml the library returns an error with the cvLoad function:

OpenCV Error: Unspecified error (The node does not represent a user object (unknown type?)) in cvRead, file /home/sachin/opencv/sachin/opencv-2.4.10/modules/core/src/persistence.cpp, line 4991
terminate called after throwing an instance of 'cv::Exception'
what(): /usr/src/RPM/BUILD/libopencv2.4-2.4.9.1/modules/core/src/persistence.cpp:4991: error: (-2) The node does not represent a user object (unknown type?) in function cvRead

What does the library mean? What kind of user object does she need and where to specify it? I understand that I should use OpenCV version 4.x, but so far I have only managed to figure out the bindings for version 2.x for my programming language (FreePascal). Bindings for version 4 are only in development.

2

what’s the code you’re trying to run? what data (data files) are you trying to run it on? where did you take that file (XML file) from?

generally, a MRE helps

3

Code:

...
//Imported function
type
TcvLoad = function(const filename: pCvChar; memstorage: pCvMemStorage = Nil; const name: pCvChar = nil;
    const real_name: ppCvChar = nil): Pointer; cdecl;
var
  cvLoad: TcvLoad;
cvLoad := ocvGetProcAddress('cvLoad', coreDLL);
...

//code for load haar
storage := cvCreateMemStorage(0);
  // Load the First HaarClassifierCascade
  if fileexists(extractfilepath(application.exename)+''+cascade_name) then
  Cascade_Name:=extractfilepath(application.exename)+''+cascade_name;
  try
    ClassifierCascade := cvLoad(pCVChar(Cascade_Name));
...

the program crashes on the line ClassifierCascade := cvLoad(pCVChar(Cascade_Name));
data files getted from github, from OpenCV repo, branch 2.4.(also tried files from archive opencv-2.4.9.zip getted from sourceforge mirror) used file: haarcascade_frontalface_alt.xml, also tried haarcascade_smile.xml and haarcascade_eye.xml

4

oh wow, that looks like it’s using the ancient OpenCV 1.x API (a C API). abandon all hope. that stuff was made obsolete with OpenCV version 2.0, which introduced C++ API.

if you abandon freepascal too, and switch to embarcadero stuff, you’ll even find a somewhat active-ish community.

you didn’t pass anything for memstorage. maybe you should. the parameters for a cascade classifier are probably not trivial enough to do without the memstorage.

generally, if you get a violated assertion, you can take that message and look for it in the source code. or see what source file and line is stated in that line of output (modules/core/src/persistence.cpp:4991).

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