How to Create OpenCV cv::Mat from NvBuffer in JetPack 5.1

Issue Overview

Users are experiencing difficulties when attempting to create an OpenCV cv::Mat object from an NvBuffer while using JetPack 5.1. The primary symptoms include:

• Incompatibility with previous methods for populating cv::Mat, specifically the outdated use of NvBufferColorFormat_ABGR32, which is no longer available.
• Users report that the generated cv::Mat displays incorrect color channels, particularly with alpha and red channels swapped.
• The issue arises during the integration of OpenCV with the Argus camera framework, particularly when using the 09_argus_camera_jpeg sample application.

The hardware specifications include the Nvidia Jetson Orin Nano Dev board, and the software context involves JetPack 5.1. Users have reported this issue consistently, indicating that it significantly impacts their ability to process images correctly in their applications.

Possible Causes

Several potential causes for this issue have been identified:

• Hardware Incompatibilities: Users may be using third-party carrier boards that do not fully support the required functionalities of the Jetson Orin Nano.
• Software Bugs or Conflicts: Changes in JetPack 5.1 may have introduced bugs or conflicts with existing codebases.
• Configuration Errors: Incorrect configurations in the integration of OpenCV and Argus may lead to improper handling of color formats.
• Driver Issues: Outdated or incompatible drivers could affect how buffers are managed and interpreted.
• User Misconfigurations: Incorrect usage of API calls or misunderstanding of new API requirements could lead to errors.

Troubleshooting Steps, Solutions & Fixes

To address the issue effectively, follow these comprehensive troubleshooting steps:

1. Verify Software Environment:

   • Ensure you are using JetPack 5.1 or later.
   • Check for any available updates or patches that may resolve known issues.

2. Replace Deprecated APIs:

   • Update your code to replace NvBufferColorFormat_ABGR32 with NVBUF_COLOR_FORMAT_RGBA. This change is crucial as it aligns with the updated API in JetPack 5.1.

3. Use Correct Color Conversion:

   • When converting color formats, use cv::COLOR_RGBA2BGR for proper channel mapping. This addresses the issue of swapped channels.

4. Update Code Snippet:

   • Here’s an updated code snippet based on user suggestions:

   auto *iNativeBuffer = Argus::interface_cast<EGLStream::NV::IImageNativeBuffer>(iFrame->getImage());
   if (!iNativeBuffer) {
       ORIGINATE_ERROR("IImageNativeBuffer not supported by Image.");
   }
   if (m_dmabuf == -1) {
       m_dmabuf = iNativeBuffer->createNvBuffer(
               streamResolution,
               NVBUF_COLOR_FORMAT_RGBA,
               NvBufferLayout_Pitch);
       if (m_dmabuf == -1) {
           ORIGINATE_ERROR("\tFailed to create NvBuffer\n");
       }
   }
   if (iNativeBuffer->copyToNvBuffer(m_dmabuf) != Argus::STATUS_OK) {
       ORIGINATE_ERROR("Failed to copy frame to NvBuffer.");
   }
   void *pdata = nullptr;
   NvBufferParams params;
   NvBufferGetParams(m_dmabuf, &params);
   NvBufferMemMap(m_dmabuf, plane, NvBufferMem_Read, &pdata);
   NvBufferMemSyncForCpu(m_dmabuf, plane, &pdata);
   cv::Mat imgbuf = cv::Mat(streamResolution.height(), streamResolution.width(), CV_8UC4, pdata, params.pitch[0]);
   cv::Mat bgr;
   cv::cvtColor(imgbuf, bgr, cv::COLOR_RGBA2BGR);
   

5. Testing Different Color Formats:

   • If issues persist, experiment with other color format flags such as NVBUF_COLOR_FORMAT_BGRA, NVBUF_COLOR_FORMAT_ARGB, and their corresponding OpenCV conversion flags until a working combination is found.

6. Patch Reference:

   • Refer to relevant patches discussed in the forum for further adjustments and examples of successful implementations.

7. Documentation and Resources:

   • Consult Nvidia’s official documentation on NvBufSurface for additional insights into buffer management.

8. Best Practices:

   • Regularly update your development environment and libraries.
   • Test your code against different configurations to isolate issues effectively.

9. Community Support:

   • Engage with community forums for additional troubleshooting tips and shared experiences from other users facing similar issues.

By following these steps and utilizing community resources, users should be able to successfully create OpenCV matrices from NvBuffers in JetPack 5.1 without encountering channel mapping issues.