Converting OpenCV Mat to Tesseract Compatible formats

OpenCV-Tesseract.md

I was primarily using the JavaCPP presets for OpenCV(JavaCV) and Tesseract

But I also found some references for C++

Here's what works for C++

#include <tesseract/baseapi.h>
#include <leptonica/allheaders.h>    
#include <opencv2/opencv.hpp>
...
char imagename[] = "testimg.jpg";
cv::Mat _mat = cv::imread(imagename);
cv::cvtColor(_mat, _mat, CV_BGR2RGBA); 
api.SetImage(_mat.data, _mat.cols, _mat.rows, 4, 4*_mat.cols);
char *outtext = api.GetUTF8Text();
...

Source: http://stackoverflow.com/a/38583706/1541263

For JavaCV, after hours of searching the web and debugging, this is what works

Mat img = imread("file.jpg");
Mat gray = new Mat();
cvtColor(img, gray, CV_BGR2GRAY);
// api is a Tesseract client which is initialised

api.SetImage(gray.data().asBuffer(),gray.size().width(),gray.size().height(),gray.channels(),gray.size1())

This is exactly what I also spent hours looking for. Thank you!

according to the API docs void tesseract::TessBaseAPI::SetImage(const Pix * pix ), it is suggested not to pass raw data to SetImage()

Pix vs raw, which to use? Use Pix where possible. A future version of Tesseract may choose to use Pix as its internal representation and discard IMAGE altogether. Because of that, an implementation that sources and targets Pix may end up with less copies than an implementation that does not.