Comments on: OpenCV cvLoadImage IOError

By: Joseph Gutierrez

Joseph Gutierrez — Thu, 03 Dec 2009 19:06:17 +0000

LOL! This happened to me with video streaming players. Somehow I corrupted the original video when sending it to the client. All I got was “video not found error”. Two days of debugging and troubleshooting. finally found it using a hex compare. Original file with streamed file. The header was corrupted.

By: Tony Rasa

Tony Rasa — Thu, 03 Dec 2009 18:47:00 +0000

@John Sonmez
LOL! Yes, yes it is.

I picked that image as a placeholder for facebook or twitter or some such social network long time ago, with the intent of replacing it with something else… and just haven’t gotten around to it yet.

AND, I’m in the process of moving some code from Python to Visual C to see if that makes any of my problems go away, or just generates new one…

By: John Sonmez

John Sonmez — Thu, 03 Dec 2009 18:37:21 +0000

@Tony Rasa If your avatar General Zod?

By: Tony Rasa

Tony Rasa — Thu, 03 Dec 2009 17:33:24 +0000

Example code from openCV source, taken wildly out of context, and with numerous syntax liberties added for blog publishing:

// gets called by loadImage()
ImageDecoder findDecoder( const string& filename ) {
  FILE* f= fopen( filename.c_str(), "rb" );
  if( !f )
    // NB: can't open file = empty ImageDecoder
    return ImageDecoder(); 

  // ..bunch of stuff happens.. and then..

  for( i = 0; i [ decoders.size(); i   ) {
    if( decoders[i].checkSignature(signature) )
      // NB: all good, return correct decoder
      return decoders[i].newDecoder();
  }
  // NB: couldn't find decoder due to bad data,
  // **take same action as if the file couldnt be opened**
  return ImageDecoder();
}

By: Tony Rasa

Tony Rasa — Thu, 03 Dec 2009 17:16:12 +0000

@John Sonmez
While I agree with you that this layer-on-layer stuff makes debugging tough, the underlying lack-of-meaningful-error issue was due the typical error handling in the granddaddy of static languages, C – “if (!whatever) return 0;”

The python wrapper just echos the [non-helpful] ERRNO and message it got from C.

By: John Sonmez

John Sonmez — Thu, 03 Dec 2009 16:53:23 +0000

A similar issue helped me make the choice for between using Watir or Watin/Watij. The main problem I had with using Watir was that debugging Ruby code is somewhat difficult when you are using someone else’s library. Its very difficult to determine where exactly is the uninformative error message coming from. With the Java and C# versions of the WatiX framework, even though some of the syntax is not as easy, the errors messages are much more clear and down to a lower level. Perhaps its just my understanding of Java and C# over Ruby, but for me the choice came down to errors like the one you posted above. There is a major trade-off between static and dynamically typed languages when it comes to debugging and # of reasons why something can go wrong.