Setup OpenCV-DNN module with CUDA backend support (For Linux)

Setup OpenCV-DNN module with CUDA backend support (For Linux)

In this tutorial, we will be building OpenCV from source with CUDA backend support (OpenCV-DNN-CUDA module).

IMPORTANT: The OpenCV-DNN module only supports inference so although you will get much faster inference out of it, the training however will be the same as was for the OpenCV we set up without CUDA backend support.


1. Install CUDA & cuDNN.

2. Install the necessary Ubuntu packages if not already installed.

3. Download and unzip opencv & opencv_contrib

4. Setup python environment

5. Configure OpenCV libraries with CMake commad

6. Build OpenCV from source for your NVidia GPU.


STEP 1) Install CUDA & cuDNN

Download and install CUDA and its corresponding cuDNN archive for your system. Go to to download the latest CUDA Toolkit. You can also download previous versions from Archive of Previous CUDA Releases OR under the Resources section at the cuda-downloads link given above. Next, download and copy the cuDNN folder and its contents to where we installed CUDA. You can download the latest version of cuDNN from . You can also download previous versions from the cudnn archive at .

Next, you need to add the paths to these in your bashrc script.

After that, reboot your system and verify your CUDA installation in a terminal by typing the following 2 commands:

nvcc -V

Follow this blog to learn how to install and set up CUDA and CUDNN on Linux.

STEP 2) Install the necessary Ubuntu packages if not already installed.

sudo apt-get update
sudo apt-get upgrade
sudo apt-get install build-essential cmake unzip pkg-config
sudo apt-get install libjpeg-dev libpng-dev libtiff-dev
sudo apt-get install libavcodec-dev libavformat-dev libswscale-dev
sudo apt-get install libv4l-dev libxvidcore-dev libx264-dev
sudo apt-get install libgtk-3-dev
sudo apt-get install libblas-dev liblapack-dev gfortran
sudo apt-get install python3-dev

STEP 3) Download and unzip opencv & opencv_contrib

Navigate to the home directory, download OpenCV archive, unzip it and rename the folder to opencv.

cd ~
wget -O
unzip -q
mv opencv-4.5.5 opencv
rm -f 

Next, download the opencv_contrib archive, unzip it and rename the folder to opencv_contrib.

Note: Make sure to download the exact same version of the opencv_contrib as the opencv archive you downloaded before that.

wget -O
unzip -q
mv opencv_contrib-4.5.5 opencv_contrib
rm -f 

STEP 4) Setup the python environment

Install virtualenv and virtualenvwrapper if you don’t have them on your system already.

sudo pip install virtualenv virtualenvwrapper

Open the bashrc script file using nano.

nano ~/.bashrc

Enter the following export paths to set the path for the virtualenvwrapper at the bottom and save the file. (Press ctrl+x , y and Enter to save the file)

export WORKON_HOME=$HOME/.virtualenvs
export VIRTUALENVWRAPPER_PYTHON=/usr/bin/python3
source /usr/local/bin/

Run source to assert the changes in the system for the bashrc script.

source ~/.bashrc

Create a virtual environment in a terminal. We will be installing the OpenCV-DNN-CUDA module in a virtual environment and not our base environment.

mkvirtualenv opencv_dnn_cuda -p python3

Install NumPy package.

pip install numpy

Activate the virtual environment by entering the following command:

workon opencv_dnn_cuda

STEP 5) Configure OpenCV using the cmake command to install some libraries

Navigate to the opencv folder we created in step 3. Create another folder inside it named build and navigate inside it.

cd ~/opencv
mkdir build
cd build

Run the CMake command to configure settings for the OpenCV you want to build from source with your custom libraries and functions selected.

Change the CUDA_ARCH_BIN parameter in the command below to your GPU’s compute capability. Find your GPU’s cc here. Also, change the virtual environment name in the PYTHON_EXECUTABLE parameter if you are using a different name else leave it as it is.

	-D OPENCV_EXTRA_MODULES_PATH=~/opencv_contrib/modules \
	-D HAVE_opencv_python3=ON \
	-D PYTHON_EXECUTABLE=~/.virtualenvs/opencv_dnn_cuda/bin/python \

In the above CMake command, we are compiling OpenCV with both CUDA and cuDNN support enabled (WITH_CUDA and WITH_CUDNN, respectively). We are also enabling the OPENCV_DNN_CUDA parameter to build the DNN module with CUDA backend support. We are also setting ENABLE_FAST_MATH, CUDA_FAST_MATH, and WITH_CUBLAS for optimization purposes.

STEP 6) Lastly, build the OpenCV-DNN module from source with CUDA backend support for your specific NVidia GPU

Run the make command to build the OpenCV with the above-configured settings. (Run nproc in terminal to print your no. of processors. Replace that with 8 below in j8.)

make -j8

This will build the OpenCV-DNN module from source with the CUDA backend. This process can take up to an hour or so.

Next, install the OpenCV on your system once it has finished building the OpenCV in the make command above. Run the following commands:

sudo make install
sudo ldconfig

Next, the final step is to create a symbolic link between the newly installed OpenCV library to our python virtual environment. For that, you need the path where the OpenCV bindings were installed. You can determine that path via the install path configuration in the CMake command step output.

In my case, the install path was lib/python3.6/site-packages/cv2/python-3.6 which means my OpenCV bindings are in /usr/local/lib/python3.6/site-packages/cv2/python-3.6. Check where your “.so” file is.

You can confirm the above path by listing its contents. Run the following ls command:

ls -l /usr/local/lib/python3.6/site-packages/cv2/python-3.6
total 10104
-rw-r--r-- 1 root staff 10345488 Mar 23 07:06

You will see an output like above confirming the cv2 binding is here. I have Python 3.6 and a 64-bit architecture which explains the file name. Your’s might vary according to your Python and system architecture.

Next, navigate to the virtual environment “site-packages” folder, and finally create a link for the cv2 bindings we found above using the ln -s command. This creates a sym-link inside the current working directory which is the site-packages folder in our virtual environment.

cd ~/.virtualenvs/opencv_dnn_cuda/lib/python3.6/site-packages/
ln -s /usr/local/lib/python3.6/site-packages/cv2/python-3.6/

Make sure to double-check everything as this command silently fails even if the path is incorrect meaning you will get no warning or error message and the output will not work. So be mindful of this step and check if the file is created or not.

That’s it! We have successfully built the OpenCV-DNN module with CUDA backend support.

Check if cv2 is installed correctly.

workon opencv_dnn_cuda

Python 3.6.9 (default, Jul 02 2019, 17:25:39)
[GCC 6.3.0 20170516] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import cv2
>>> cv2.__version__

Check if the OpenCV is installed correctly with CUDA backend support using the script below. Download it below.

import numpy as np
import cv2 as cv
import time

npTmp = np.random.random((1024, 1024)).astype(np.float32)

npMat1 = np.stack([npTmp,npTmp],axis=2)
npMat2 = npMat1

cuMat1 = cv.cuda_GpuMat()
cuMat2 = cv.cuda_GpuMat()

start_time = time.time()
cv.cuda.gemm(cuMat1, cuMat2,1,None,0,None,1)

print("CUDA using GPU --- %s seconds ---" % (time.time() - start_time))

start_time = time.time()

print("CPU --- %s seconds ---" % (time.time() - start_time))

Download the test_DNN_CV script below.

My YouTube Video on this!

Next Tutorial:

Run YOLOv4 inference using OpenCV-DNN Module on Linux

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