# SimpleBlobDetector crash **URL:** \ **Category:** Python\ **Tags:** features2d\ **Created:** [January 23, 2021, 1:48pm UTC](https://forum.opencv.org/t/simpleblobdetector-crash/1076 "2021-01-23T13:48:35Z")\ **Posts on this page:** 5\ **Page:** 1
**Author:** ![Devon](https://avatars.discourse-cdn.com/v4/letter/d/f9ae1b/32.png) [@Devon](https://forum.opencv.org/u/Devon)\ **Post date:** [January 23, 2021, 1:48pm UTC](https://forum.opencv.org/t/simpleblobdetector-crash/1076/1 "2021-01-23T13:48:35Z")
cv2.SimpleBlobDetector().detect(…) coredumps trying to dereference address zero. ``` Peace --Devon ``` P.S. Any cure for the annoying echo of every input line? ``` $ lldb python3 lldb python3 (lldb) target create "python3" Current executable set to 'python3' (x86_64). (lldb) run run Process 34431 launched: '/Library/Frameworks/Python.framework/Versions/3.7/bin/python3' (x86_64) Process 34431 stopped * thread #2, stop reason = exec frame #0: 0x0000000100004000 dyld`_dyld_start dyld`_dyld_start: -> 0x100004000 <+0>: popq %rdi 0x100004001 <+1>: pushq $0x0 0x100004003 <+3>: movq %rsp, %rbp 0x100004006 <+6>: andq $-0x10, %rsp Target 0: (Python) stopped. (lldb) continue continue Process 34431 resuming Python 3.7.3 (v3.7.3:ef4ec6ed12, Mar 25 2019, 16:52:21) [Clang 6.0 (clang-600.0.57)] on darwin Type "help", "copyright", "credits" or "license" for more information. >>> import cv2 print(cv2. __version__ ) im = cv2.imread("/tmp/portrait.jpg", cv2.IMREAD_GRAYSCALE) print(im) print(cv2.SimpleBlobDetector().detect(im)) >>> import cv2 >>> print(cv2. __version__ ) 4.5.1 >>> im = cv2.imread("/tmp/portrait.jpg", cv2.IMREAD_GRAYSCALE) >>> print(im) [[23 23 23 ... 13 13 13] [23 23 23 ... 13 13 13] [23 23 23 ... 13 13 13] ... [254 254 254 ... 144 145 145] [254 254 254 ... 147 146 146] [254 254 254 ... 150 148 148]] >>> print(cv2.SimpleBlobDetector().detect(im)) Process 34431 stopped * thread #2, queue = 'com.apple.main-thread', stop reason = EXC_BAD_ACCESS (code=1, address=0x0) frame #0: 0x0000000102cf1432 cv2.cpython-37m-darwin.so`pyopencv_cv_Feature2D_detect(_object*, _object*, _object*) + 386 cv2.cpython-37m-darwin.so`pyopencv_cv_Feature2D_detect: -> 0x102cf1432 <+386>: movq (%rdi), %rax 0x102cf1435 <+389>: movq 0x40(%rax), %rax 0x102cf1439 <+393>: movq $0x0, -0xb0(%rbp) 0x102cf1444 <+404>: movl $0x1010000, -0xc0(%rbp) ; imm = 0x1010000 Target 0: (Python) stopped. (lldb) bt all bt all * thread #2, queue = 'com.apple.main-thread', stop reason = EXC_BAD_ACCESS (code=1, address=0x0) * frame #0: 0x0000000102cf1432 cv2.cpython-37m-darwin.so`pyopencv_cv_Feature2D_detect(_object*, _object*, _object*) + 386 frame #1: 0x00000001000f05ed Python`_PyMethodDef_RawFastCallKeywords + 685 frame #2: 0x00000001000f6152 Python`_PyMethodDescr_FastCallKeywords + 82 frame #3: 0x00000001001ae5dc Python`call_function + 780 frame #4: 0x00000001001ab55c Python`_PyEval_EvalFrameDefault + 25164 frame #5: 0x00000001001af0d6 Python`_PyEval_EvalCodeWithName + 2422 frame #6: 0x00000001001a5234 Python`PyEval_EvalCode + 100 frame #7: 0x00000001001e24e7 Python`PyRun_InteractiveOneObjectEx + 599 frame #8: 0x00000001001e1d52 Python`PyRun_InteractiveLoopFlags + 226 frame #9: 0x00000001001e1c3c Python`PyRun_AnyFileExFlags + 60 frame #10: 0x0000000100201ac6 Python`pymain_main + 7110 frame #11: 0x0000000100201f2a Python`_Py_UnixMain + 58 frame #12: 0x00007fff685773d5 libdyld.dylib`start + 1 thread #3 frame #0: 0x00007fff686ac322 libsystem_kernel.dylib`swtch_pri + 10 frame #1: 0x00007fff6876de90 libsystem_pthread.dylib`sched_yield + 11 frame #2: 0x00000001099eb1bb libopenblas.0.dylib`blas_thread_server + 123 frame #3: 0x00007fff6876b2eb libsystem_pthread.dylib`_pthread_body + 126 frame #4: 0x00007fff6876e249 libsystem_pthread.dylib`_pthread_start + 66 frame #5: 0x00007fff6876a40d libsystem_pthread.dylib`thread_start + 13 (lldb) ``` ---
**Author:** ![crackwitz](https://sea2.discourse-cdn.com/flex020/user_avatar/forum.opencv.org/crackwitz/32/14_2.png) [@crackwitz](https://forum.opencv.org/u/crackwitz)\ **Post date:** [January 23, 2021, 5:26pm UTC](https://forum.opencv.org/t/simpleblobdetector-crash/1076/2 "2021-01-23T17:26:35Z")
you aren’t instantiating correctly. OpenCV always needs you to use the `create` method of a class to create an instance. This goes for the C++ API as well as the Python API. cv2.SimpleBlobDetector. **create** ().detect(…) # python cv2.SimpleBlobDetector\_create().detect(…) # python, alternative and it would be a very good idea to keep a reference to that instance, i.e.: ```auto detector = cv2.SimpleBlobDetector.create() detector.detect(...) ``` ---
**Author:** ![Devon](https://avatars.discourse-cdn.com/v4/letter/d/f9ae1b/32.png) [@Devon](https://forum.opencv.org/u/Devon)\ **Post date:** [January 24, 2021, 3:04am UTC](https://forum.opencv.org/t/simpleblobdetector-crash/1076/3 "2021-01-24T03:04:30Z")
Thanks, that works. Was it always so? I see no mention of **create** in the SimpleBlobDetector docs and “tested” examples. ---
**Author:** ![crackwitz](https://sea2.discourse-cdn.com/flex020/user_avatar/forum.opencv.org/crackwitz/32/14_2.png) [@crackwitz](https://forum.opencv.org/u/crackwitz)\ **Post date:** [January 24, 2021, 11:43am UTC](https://forum.opencv.org/t/simpleblobdetector-crash/1076/4 "2021-01-24T11:43:10Z")
what docs and examples would those be? are you working with v2.4 docs? you really must not do that. if it’s not v2.4 docs you’re talking about, I would very much like to know very specifically what you’re referring to. links at least, or citations. not a rhetorical question. current docs on that class have pretty much one (static) method and it is `create` (others inherited/overridden from superclasses) and even the docs for v3.0.0 have it. even v2.4 docs show use of cv::Ptr in most places. [OpenCV: cv::SimpleBlobDetector Class Reference](https://docs.opencv.org/master/d0/d7a/classcv_1_1SimpleBlobDetector.html#a1d7a06c8b8749207a978e42cd8d0cdf6) ---
**Author:** ![Devon](https://avatars.discourse-cdn.com/v4/letter/d/f9ae1b/32.png) [@Devon](https://forum.opencv.org/u/Devon)\ **Post date:** [January 25, 2021, 1:10pm UTC](https://forum.opencv.org/t/simpleblobdetector-crash/1076/5 "2021-01-25T13:10:46Z")
Thanks for the link but it’s time to go meta. Robo-docs are worse than useless, and this one in particular doesn’t even mention the methods I initially used. The mere existence of **create** suggests no such requirement to anyone who missed OpenCV summer camp, especially given the examples I followed (alas, those browser tabs are gone) and consequent cryptic coredump message. A link to the source might be a slight improvement but actual examples are best. How to add examples to that skimpy _Class Reference_? I need to find or make a libre OpenCV IDE with auto completion, auto chaining, electric documentation, the works — does it exist?