Real-Time QR Code Recognition on reCamera

Introduction

This example demonstrates how to build a real-time QR code recognition system using reCamera. The system captures live video frames through the camera, decodes QR codes using the ZXing library, and pushes the video frames (JPEG) along with the recognition results to a PC via UDP for display.

Key Features:

• Real-time camera capture and QR code recognition
• Supports both video streaming mode and single-image mode
• Pushes JPEG frames + recognition results to the PC via UDP
• Detailed performance statistics (capture FPS, decode FPS, average decode time)
• Python receiver script on the PC for real-time video and result display

How It Works

Video Streaming Mode (Default)

The real-time recognition flow is as follows:

1. Camera Capture: Captures RGB888 frames (default 640×480) through the sscma-micro Camera interface
2. Grayscale Conversion: Converts the RGB888 image to grayscale (required for QR code recognition)
3. ZXing Decoding: Uses MultiFormatReader + HybridBinarizer for barcode detection and decoding (TryHarder is disabled by default to maintain real-time performance)
4. Result Output: Prints the decoded content to the terminal when a new QR code is detected
5. UDP Push: Sends the JPEG frame + recognition result to the PC via the SeSg stream_udp component

In video scenarios, ZXing incurs significant search overhead when "no code is found." To ensure real-time performance, the program uses a 150ms decode throttling strategy — it performs decoding once every 150ms instead of on every frame. This drastically reduces CPU load without compromising the recognition experience.

Demo Setup

To set up this demo, you need to:

1. Cross-compile the C++ program on your PC
2. Run the compiled executable on the ReCamera
3. Run the Python receiver script on your PC

1. Compile the C++ Program

note

Before building this solution, make sure you have configured the ReCamera-OS environment (version 0.2.1 or later) according to the main project documentation, including the SDK path and cross-compilation toolchain.

Set the environment variable for the cross-compilation toolchain:

export PATH='current compile chain path'/host-tools/gcc/riscv64-linux-musl-x86_64/bin:$PATH

Clone the repository and navigate to the solution directory to compile. Run the following commands step by step in your PC terminal. If you have already downloaded and configured the cross-compilation environment following the Developing with C/C++ documentation, you can directly run the compile commands below.

git clone https://github.com/RobotXTeam/sscma-example-sg200x.git
cd sscma-example-sg200x/solutions/sesg-project/qrcode-udp
export SG200X_SDK_PATH='current clone path'/sg2002_recamera_emmc
## compile cmd
rm -rf build && mkdir build && cd build 
cmake -DCMAKE_BUILD_TYPE=Release -DCMAKE_CXX_FLAGS="-std=c++17" ..
make -j$(nproc)

After compilation, the executable is located at build/qrcode_udp. Upload it to the ReCamera at /home/recamera/ using the scp command:

sudo scp qrcode_udp [email protected]:/home/recamera/  # Replace 192.168.4.53 with your reCamera's IP address

Enter the password for the corresponding platform when prompted to complete the transfer of qrcode_udp.

2. Configure ReCamera

warning

Before running the C++ program, you must stop the default Node-RED services as they occupy the camera resources. Run the following commands via SSH:

sudo /etc/init.d/S03node-red stop
sudo /etc/init.d/S91sscma-node stop
sudo /etc/init.d/S93sscma-supervisor stop

3. Run the Executable on ReCamera

Then run the following command to grant execution permission:

chmod +x qrcode_udp

Parameters

Parameter	Description	Default
udp_ip	PC IP address (enables UDP streaming)	192.168.4.48
udp_port	UDP port number	5001

Example Commands

Video streaming mode (no UDP streaming, local recognition only):

sudo ./qrcode_udp

Video streaming mode + UDP streaming:

sudo ./qrcode_udp 192.168.4.48 5001

note

Please replace 192.168.4.48 with the actual IP address of your PC on the same network as the ReCamera.

On the ReCamera Terminal

Video streaming mode — The program will display performance statistics once per second:

[Performance] CaptureFPS=2.60 | DecodeFPS=2.60 | AvgDecodeTime=323.0ms | DecodeSuccess=0 | NewCode=0
[Performance] CaptureFPS=1.94 | DecodeFPS=1.94 | AvgDecodeTime=434.0ms | DecodeSuccess=0 | NewCode=0
[QRCode] https://wiki.seeedstudio.com/recamera_software_docs/
[Performance] CaptureFPS=4.45 | DecodeFPS=4.45 | AvgDecodeTime=174.8ms | DecodeSuccess=3 | NewCode=1
[Performance] CaptureFPS=4.62 | DecodeFPS=4.62 | AvgDecodeTime=163.6ms | DecodeSuccess=5 | NewCode=0
[Performance] CaptureFPS=4.86 | DecodeFPS=4.86 | AvgDecodeTime=165.4ms | DecodeSuccess=3 | NewCode=0
[Performance] CaptureFPS=4.60 | DecodeFPS=4.60 | AvgDecodeTime=169.8ms | DecodeSuccess=4 | NewCode=0
[Performance] CaptureFPS=4.33 | DecodeFPS=4.33 | AvgDecodeTime=184.4ms | DecodeSuccess=5 | NewCode=0
[Performance] CaptureFPS=2.78 | DecodeFPS=2.78 | AvgDecodeTime=305.8ms | DecodeSuccess=3 | NewCode=0
[Performance] CaptureFPS=1.96 | DecodeFPS=1.96 | AvgDecodeTime=404.0ms | DecodeSuccess=2 | NewCode=0
[Performance] CaptureFPS=4.72 | DecodeFPS=4.72 | AvgDecodeTime=166.0ms | DecodeSuccess=6 | NewCode=0
[Performance] CaptureFPS=4.56 | DecodeFPS=4.56 | AvgDecodeTime=178.5ms | DecodeSuccess=6 | NewCode=0
[QRCode] zxj
[Performance] CaptureFPS=5.32 | DecodeFPS=5.32 | AvgDecodeTime=145.3ms | DecodeSuccess=7 | NewCode=1
[Performance] CaptureFPS=5.30 | DecodeFPS=5.30 | AvgDecodeTime=149.1ms | DecodeSuccess=6 | NewCode=0
[Performance] CaptureFPS=4.70 | DecodeFPS=4.70 | AvgDecodeTime=170.8ms | DecodeSuccess=5 | NewCode=0
[Performance] CaptureFPS=1.85 | DecodeFPS=1.85 | AvgDecodeTime=455.0ms | DecodeSuccess=1 | NewCode=0

• CaptureFPS: Camera capture frame rate
• DecodeFPS: Actual frame rate at which decoding is executed (limited by the 150ms throttle)
• AvgDecodeTime: Average time taken for a single ZXing decode
• DecodeSuccess: Number of times a QR code was successfully recognized
• NewCode: Number of times the QR code text changed

4. Run the Python Receiver on PC

On your PC, ensure Python with the required libraries is installed:

pip install opencv-python numpy

Navigate to the solution directory and run:

cd sscma-example-sg200x/solutions/sesg-project/qrcode-udp
python tools/udp_receiver.py --port 5001 --show --print-dets

Python Receiver Parameters

Parameter	Description	Default
--ip	Listen IP address	0.0.0.0
--port	Listen port	5001
--show	Display the video window	off
--print-dets	Print the recognized QR code text	off

On the Python Receiver Window

The PC will display a live video window that includes:

• The JPEG video stream
• When a QR code is recognized, the decoded text is overlaid in the top-left corner of the frame (yellow font)
• The frame number (green font)

Dependencies

Dependency	Description	Source
sscma-micro	Camera access (Device, Camera interfaces)	Repository component components/sscma-micro
stream_udp	UDP streaming (JPEG + detection results)	Repository component components/SeSg/stream_udp
OpenCV (core, imgproc, imgcodecs)	Image processing, grayscale conversion, downsampling	SG200X SDK sysroot
ZXing (libzxing)	Multi-format barcode/QR code decoding	SG200X SDK sysroot
ReCameraOS ≥ 0.2.1	Runtime environment	Device firmware

Troubleshooting

Camera Access Error

If you see a "No camera device found" error:

• Ensure the Node-RED services are stopped (see Step 2 above)
• Check the camera connection

UDP Connection Failed

If the PC doesn't receive data:

• Verify that the PC and ReCamera are on the same network
• Check the firewall settings on the PC
• Confirm that UDP port 5001 is not blocked
• Use ping to test connectivity between the devices

QR Code Recognition Failure

If the camera view contains a QR code but it isn't recognized:

• Ensure the QR code is large enough and clear in the frame
• Avoid excessive blur, rotation, or uneven lighting
• Note that TryHarder mode is disabled by default to prioritize real-time performance

Compilation Error

If you encounter compilation errors related to ZXing or sscma-micro:

• Confirm that the SG200X_SDK_PATH environment variable is set correctly
• Ensure the toolchain path is added to the PATH environment variable
• Check that the repository submodules are fully pulled (git submodule update --init --recursive)

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