C++ Demo - Image Classification (PPResNet)

[ryan1288]

This PR adds the C++ demo for the Image Classification PPResNet model, as part of a request from #135.

• demo.cpp: Added to have matching functionality to demo.py. All 1,000 classes included as a string to be parsed.
• demo.py: Printout was adjusted be cleaner and matches the C++ version.
• CMakeLists.txt: Created to build with OpenCV 4.9.0 and enforces C++11 standards upon building.
• README.md: Updated with C++ instructions.

The interface matches other C++ demos within the set of ML models.

The predictions visualizations were adjusted for both C++ and Python demos for clarity.
Before (Python)

After (Python & C++)

Testing

• Matching Python and C++ demo classifcations
  A number of images were tested with top-k = 20 and all had matching output classes, with one example provided below.
  
  
• Run demo with top-k = 1

cmake -B build -D OPENCV_INSTALLATION_PATH=/path/to/opencv .
cmake --build build
./build/opencv_zoo_image_classification_ppresnet --input=example_input/goldfish.jpg

• Run demo with top-k > 1

cmake -B build -D OPENCV_INSTALLATION_PATH=/path/to/opencv .
cmake --build build
./build/opencv_zoo_image_classification_ppresnet --input=example_input/goldfish.jpg --top_k=5

[fengyuentau]

Merge this file with demo.cpp and revert the changes in ppresnet.py. We made a decision long time ago that demo should be portable and convenient as much as possible with less files.

[ryan1288]

Updated! I've reverted the changes to ppresnet.py and merged the labels with demo.cpp. Agree with the portability 😄 .

[fengyuentau]

I don't think we need example input as it demonstrates nothing and it increase repo size.

[ryan1288]

Removed example 👍

[fengyuentau]

How about using std::vector<std::string>? In this case we do not need to duplicate \n for each class and we do not need to re-load this in loadLabels.

[ryan1288]

@fengyuentau That's a great idea. Not sure why I didn't think of that 😅 I've updated it.

[fengyuentau]

Thank you for the contribution! 👍