cv::Mat::reshape does not work anymore in 2.4.0! :( (Bug #1942)

Added by Vito Macchia almost 13 years ago. Updated almost 13 years ago.

Status:Done Start date:2012-05-16
Priority:High Due date:
Assignee:Andrey Kamaev % Done:

0%
Category:core
Target version:2.4.1
Affected version: Operating System:
Difficulty: HW Platform:
Pull request:

Description

Hi, yesterday I upgraded from OpenCV 2.3.1 to 2.4.0 and this resulted in breaking up my code at a very basic level, that is cv::Mat::reshape.
It does not work anymore because it rises this very odd error:

OpenCV Error: The function/feature is not implemented () in reshape, file /home/vito/SourceFolders/OpenCV-2.4.0/modules/core/src/matrix.cpp, line 2891
terminate called after throwing an instance of 'cv::Exception'
  what():  /home/vito/SourceFolders/OpenCV-2.4.0/modules/core/src/matrix.cpp:2891: error: (-213)  in function reshape

Annullato (core dump creato)

I was just computing (correctly up to last release) a n by 3 matrix centroid!!!
The code that causes this issue is like this:

cv::Mat A = (cv::Mat_<float>(18,3)<<
            3.4884074, 1.4159607, 0.78737736,
                  2.3456569, -0.88010466, 0.3009364,
                  2.2710831, -0.81703609, -0.035067264,
                  4.2535844, 1.639971, -0.050906904,
                  2.3350885, -0.95192128, -0.0438799,
                  2.1784587, -0.44972348, -0.030304601,
                  2.0178607, -0.37849408, -0.36985111,
                  5.4491558, 1.6346338, 1.47364,
                  2.0937307, -0.55370253, -0.61064941,
                  2.2241848, -0.77611613, -0.65611577,
                  2.2629843, -0.73538947, -0.061620831,
                  6.0119362, 2.1610513, -0.35381731,
                  2.0254273, -0.39233872, -0.42393345,
                  2.2760479, -0.71189457, -0.60599393,
                  2.0163939, -0.39841026, -0.60027134,
                  2.1354396, -0.40491298, -0.30758607,
                  2.3370185, -0.62746048, -0.49580219,
                  2.0175889, -0.41587964, -0.46615571
            );
    cv::Mat_<float> M= A.reshape(3); //<-- code breaks here in 2.4.0

  Scalar s = mean (M);
  Point3f centroid = Point3f (s[0], s[1], s[2]);

Associated revisions

Revision 5f9e295a
Added by Andrey Kamaev almost 13 years ago

Added test and workaround for #1942

Revision f36858b3
Added by Andrey Pavlenko over 11 years ago

Merge pull request #1942 from ilya-lavrenov:warn_fix

History

#1
Updated by Andrey Kamaev almost 13 years ago

It seems that you are using wrong headers or have a link problem.

Mat class defines 2 versions of reshape method:

1Mat reshape(int _cn, int _rows=0) const;
2Mat reshape(int _cn, int _newndims, const int* _newsz) const;

And you need the first one, but your exception comes from the second overload.

  • Status changed from Open to Cancelled
  • Target version set to 2.4.1
  • Category set to core
  • Assignee set to Andrey Kamaev

#2
Updated by Vito Macchia almost 13 years ago

Yes but iven if I try with:

    cv::Mat_<float> M= A.reshape(3,A.rows);

code breaks!
And yes I know there is an overload (though, according to the documentation, the second form should be for MatND)
But calling with one single argument should call the first form, not the second.

You mentioned an header problem. Which header should I include then? I was including just this:
#include <opencv2/core/core.hpp>

and up to 2.3.1 was ok. I compiled it from source on Ubuntu 12.04 using the same CMake settings I used for 2.3.1

#3
Updated by Andrey Kamaev almost 13 years ago

Well, I've reproduced your problem.
Test and partial fix are committed to OpenCV trunk.

By the way you are using cv::Mat_<float> in a wrong way. It can not be 3-channel. For 3-channel Mat you need a cv::Mat_<cv::Vec3f>.
See the last paragraph for multi-channel Mat_: http://docs.opencv.org/modules/core/doc/basic_structures.html#Mat_

So the copy constructor internally tries to reshape the Mat back to single channel.

  • Status changed from Cancelled to Done

#4
Updated by Vito Macchia almost 13 years ago

Indeed you are right..
It was a code I wrote a long time ago, that I was just trying to run with the new release. I will fix my code using Mat_<Vec3f> for 3 channels matrices, thank you! ;)

Also available in: Atom PDF