This Viam vision service module uses tesseract-ocr through the gosseract wrapper and allows you to process an image extract text information from it. An example could be to extract license plate information to automatically open gates etc.
Tesseract is incredibly powerful and provides a vast variety of configuration parameters. The most important setting is the page segmentation mode tessedit_pageseg_mode. This article provides a great overview over the different modes: https://pyimagesearch.com/2021/11/15/tesseract-page-segmentation-modes-psms-explained-how-to-improve-your-ocr-accuracy/
Add this sample configuration to the smart machine "components" part either in RAW JSON mode or through the we user interface by choosing "local service" in the menu.
{
"name": "license-plates",
"type": "vision",
"namespace": "rdk",
"model": "felixreichenbach:vision:ocr",
"attributes": {
"languages": [
"eng"
],
"parameters": {
"tessedit_char_blacklist": "*+",
"tessedit_pageseg_mode": "7"
},
"tessdata_local": "./tessdata/",
"tessdata_remote": "https://github.com/tesseract-ocr/tessdata_fast/raw/main/"
}
}
You can find a table of all possible tesseract configuration attributes here.
From within the "src" directory run:
go build -o ../bin/ocr .
To be able to successfully build the module, the following libraries are required. I also uninstalled leptonica and tesseract with brew ignoring dependencies as mentioned here: otiai10/gosseract#234 (comment)
wget http://www.leptonica.org/source/leptonica-1.78.0.tar.gz or https://github.com/DanBloomberg/leptonica/releases/tag/1.84.1
tar -xzvf leptonica-1.78.0.tar.gz
cd leptonica-1.78.0
./configure
make && sudo make install
brew install automake
git clone https://github.com/tesseract-ocr/tesseract.git
cd tesseract
./autogen.sh
./configure
make
sudo make install
sudo apt install build-essential
sudo apt install pkg-config
# If Unable to find a valid copy of libtoolize or glibtoolize in your PATH!
sudo apt-get install libtool
sudo apt install libjpeg-dev
sudo apt-get install libleptonica-dev
# Install tesseract libraries
git clone https://github.com/tesseract-ocr/tesseract.git
cd tesseract
./autogen.sh
./configure
# make seems not required -> done as part of the next step
sudo make install
go build -o ../bin/ocr .
alternatively:
CGO_ENABLED=1 GOARCH=arm64 go build --ldflags '-extldflags "-fopenmp -L/usr/local/lib/ -Bstatic -ltesseract"' -o ../bin/tesseract-ocr .
# Check dynamically linked libs on file
ldd fileName
# Missing tesseract lib fixed with:
sudo ldconfig
# Build go binary with adding tesseract library statically
go build --ldflags '-extldflags "-fopenmp -L/usr/local/lib/ -Bstatic -ltesseract"' -o ../bin/tesseract-ocr .
Sample makefile: https://github.com/jeremyrhyde/viam-rplidar/blob/main/Makefile
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