Working bare minimum example illustrating integration of OpenCV with ReactNative in both iOS and Android.
Doc with all steps
OpenCV Version = 4.2.0 React Native Version = 0.63.2
In this repo, we've added a BlackAndWhite function to both iOS and Android native code which coverts an image into grayscale using OpenCV and the same is accessed in RN JavaScript using {NativeModules}
References: A great Tutorial