[Python] cuda commands from python in opencv fail

I've compiled opencv with cuda support and am trying to use some cuda functions - to that end I'm trying the following test:

import cv2
if cv2.cuda.getCudaEnabledDeviceCount() > 0:
print("OpenCV was built with CUDA support.")
else:
print("OpenCV was not built with CUDA support.")
build_info = cv2.getBuildInformation()
#print(build_info)


print("\n=== CPU flags ===")
for line in build_info.splitlines():
if "math" in line.lower() or "fast" in line.lower():
print(line)
print("\n=== CUDA section ===")
for line in build_info.splitlines():
if "CUDA" in line or "FAST_MATH" in line:
print(line)



# Check if a CUDA-enabled GPU is available
if not cv2.cuda.getCudaEnabledDeviceCount():
print("CUDA-enabled GPU not found.")
# Fallback to a CPU implementation if needed
exit()

# Load an image using CPU

# Load an image
image = cv2.imread('/home/jeremy/Documents/drone_detect/laser_turret/scout_software/obsidian.jpg')
if image is None:
print("Error loading image.")
exit()

# Convert to GRAY on CPU (CUDA filter prefers 1 or 4 channels)
gray = cv2.cvtColor(image, cv2.COLOR_BGR2GRAY)
print("gray:", gray.shape, gray.dtype, gray.flags['C_CONTIGUOUS'])
# Upload to GPU
gpu_image = cv2.cuda_GpuMat()
gpu_image.upload(gray)
assert isinstance(gpu_image, cv2.cuda_GpuMat)
# Create and apply CUDA Gaussian (type = CV_8UC1)


# sanity: uploaded image must be 8UC1 and non-empty
assert isinstance(gpu_image, cv2.cuda_GpuMat) and not gpu_image.empty()
assert gpu_image.type() == cv2.CV_8UC1, f"type={gpu_image.type()} (need CV_8UC1)"

gaussian_filter = cv2.cuda.createGaussianFilter(cv2.CV_8UC1, cv2.CV_8UC1, (15, 15), 0)

# some Python bindings require an explicit dst GpuMat
dst_gpu = cv2.cuda_GpuMat()
gaussian_filter.apply(gpu_image, dst_gpu)

gpu_blurred_image = dst_gpu



# Display or save the blurred image
cv2.imshow('Original Image', image)
cv2.imshow('Blurred Image', gpu_blurred_image.download()) # this is gray

cv2.waitKey(0)
cv2.destroyAllWindows()


This invariably hits problems along the lines of

OpenCV was built with CUDA support.
=== CPU flags ===
C++ flags (Release): -fsigned-char -ffast-math -fno-finite-math-only -W -Wall -Wreturn-type -Wnon-virtual-dtor -Waddress -Wsequence-point -Wformat -Wformat-security -Wmissing-declarations -Wundef -Winit-self -Wpointer-arith -Wshadow -Wsign-promo -Wuninitialized -Wsuggest-override -Wno-delete-non-virtual-dtor -Wno-comment -Wimplicit-fallthrough=3 -Wno-strict-overflow -fdiagnostics-show-option -pthread -fomit-frame-pointer -ffunction-sections -fdata-sections -msse3 -fvisibility=hidden -fvisibility-inlines-hidden -O3 -DNDEBUG -DNDEBUG
C++ flags (Debug): -fsigned-char -ffast-math -fno-finite-math-only -W -Wall -Wreturn-type -Wnon-virtual-dtor -Waddress -Wsequence-point -Wformat -Wformat-security -Wmissing-declarations -Wundef -Winit-self -Wpointer-arith -Wshadow -Wsign-promo -Wuninitialized -Wsuggest-override -Wno-delete-non-virtual-dtor -Wno-comment -Wimplicit-fallthrough=3 -Wno-strict-overflow -fdiagnostics-show-option -pthread -fomit-frame-pointer -ffunction-sections -fdata-sections -msse3 -fvisibility=hidden -fvisibility-inlines-hidden -g -O0 -DDEBUG -D_DEBUG
C flags (Release): -fsigned-char -ffast-math -fno-finite-math-only -W -Wall -Wreturn-type -Waddress -Wsequence-point -Wformat -Wformat-security -Wmissing-declarations -Wmissing-prototypes -Wstrict-prototypes -Wundef -Winit-self -Wpointer-arith -Wshadow -Wuninitialized -Wno-comment -Wimplicit-fallthrough=3 -Wno-strict-overflow -fdiagnostics-show-option -pthread -fomit-frame-pointer -ffunction-sections -fdata-sections -msse3 -fvisibility=hidden -O3 -DNDEBUG -DNDEBUG
C flags (Debug): -fsigned-char -ffast-math -fno-finite-math-only -W -Wall -Wreturn-type -Waddress -Wsequence-point -Wformat -Wformat-security -Wmissing-declarations -Wmissing-prototypes -Wstrict-prototypes -Wundef -Winit-self -Wpointer-arith -Wshadow -Wuninitialized -Wno-comment -Wimplicit-fallthrough=3 -Wno-strict-overflow -fdiagnostics-show-option -pthread -fomit-frame-pointer -ffunction-sections -fdata-sections -msse3 -fvisibility=hidden -g -O0 -DDEBUG -D_DEBUG
Unavailable: alphamat cannops cvv fastcv hdf java julia matlab ovis python2 sfm viz
NVIDIA CUDA: YES (ver 12.9, CUFFT CUBLAS FAST_MATH)

=== CUDA section ===
NVIDIA CUDA: YES (ver 12.9, CUFFT CUBLAS FAST_MATH)
gray: (1451, 2194) uint8 True
Traceback (most recent call last):
File "<frozen runpy>", line 198, in _run_module_as_main
File "<frozen runpy>", line 88, in _run_code
File "/home/jeremy/Documents/drone_detect/laser_turret/shared/verify_opencv_cuda.py", line 53, in <module>
gaussian_filter.apply(gpu_image, dst_gpu)
cv2.error: OpenCV(4.13.0-dev) :-1: error: (-5:Bad argument) in function 'apply'
> Overload resolution failed:
> - src is not a numpy array, neither a scalar
> - Expected Ptr<cv::cuda::GpuMat> for argument 'src'
> - Expected Ptr<cv::UMat> for argument 'src'


So what is going wrong here - I have an nividia A1000 gpu and compiled opencv using the following cmake command:

cmake -G "Unix Makefiles"
-D CMAKE_BUILD_TYPE=Release
-D CMAKE_INSTALL_PREFIX=/usr/local
-D OPENCV_EXTRA_MODULES_PATH=$HOME/opencv_contrib/modules
-D BUILD_opencv_highgui=ON
-D WITH_GTK=ON
-D WITH_OPENGL=ON
-D WITH_CUDA=ON
-D WITH_CUDNN=ON
-D WITH_CUBLAS=ON
-D OPENCV_DNN_CUDA=ON
-D CUDA_ARCH_BIN=8.6
-D CUDAToolkit_ROOT=/usr/local/cuda
-D BUILD_opencv_cudacodec=ON
-D WITH_NVCUVENC=OFF
-D BUILD_EXAMPLES=ON
-D BUILD_PYTHON_SUPPORT=ON
-D INSTALL_PYTHON_EXAMPLES=ON
-D BUILD_TESTS=ON
-D BUILD_PERF_TESTS=OFF
-D BUILD_opencv_python3=ON
-D Python3_EXECUTABLE="$PYEXE"
-D Python3_NumPy_INCLUDE_DIRS="$NUMPY_INC"
-D OPENCV_PYTHON3_INSTALL_PATH=/home/jeremy/Documents/drone_detect/myenv/lib/python3.12/site-packages
-D OPENCV_PYTHON3_LIMITED_API=OFF
-D CUDA_FAST_MATH=ON
-D ENABLE_FAST_MATH=ON ..

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