OpenCV Number OCR - Image progressing (Filterin) - c++

Question

I success fully cleaned image but there is problem when I clean it with inRange I got error on cvtColor here is my code:
// generate_data.cpp
#include <opencv2/core/core.hpp>
#include <opencv2/highgui/highgui.hpp>
#include <opencv2/imgproc/imgproc.hpp>
#include <opencv2/ml/ml.hpp>
#include <iostream>
#include <vector>
// global variables ///////////////////////////////////////////////////////////////////////////////
const int MIN_CONTOUR_AREA = 20;
const int MAX_CONTOUR_AREA = 75;
const int RESIZED_IMAGE_WIDTH = 20;
const int RESIZED_IMAGE_HEIGHT = 30;
///////////////////////////////////////////////////////////////////////////////////////////////////
using namespace std;
using namespace cv;
Mat redFilter(const Mat& src)
{
assert(src.type() == CV_8UC3);
Mat redOnly;
inRange(src, Scalar(0, 0, 0), Scalar(0, 0, 0), redOnly);
return redOnly;
}
int main() {
cv::Mat matTrainingNumbers; // input image
cv::Mat matGrayscale; //
cv::Mat matBlurred; // declare various images
cv::Mat matThresh; //
cv::Mat matThreshCopy; //
std::vector<std::vector<cv::Point> > ptContours; // declare contours vector
std::vector<cv::Vec4i> v4iHierarchy; // declare contours hierarchy
cv::Mat matClassificationInts; // these are our training classifications, note we will have to perform some conversions before writing to file later
// these are our training images, due to the data types that the KNN object KNearest requires,
cv::Mat matTrainingImages; // we have to declare a single Mat, then append to it as though it's a vector,
// also we will have to perform some conversions before writing to file later
// possible chars we are interested in are digits 0 through 9, put these in vector intValidChars
std::vector<int> intValidChars = { '0', '1', '2', '3', '4', '5', '6', '7', '8', '9' };
matTrainingNumbers = cv::imread("training_numbers.png"); // read in training numbers image
if (matTrainingNumbers.empty()) { // if unable to open image
std::cout << "error: image not read from file\n\n"; // show error message on command line
return(0); // and exit program
}
matTrainingNumbers = cv::Scalar::all(255) - matTrainingNumbers; // tranfsorm to inverse
matTrainingNumbers = redFilter(matTrainingNumbers); // Convert all colors to black
matTrainingNumbers = cv::Scalar::all(255) - matTrainingNumbers; // tranfsorm to inverse
cv::imshow("Cleared numbers", matTrainingNumbers);
cv::cvtColor(matTrainingNumbers, matGrayscale, CV_BGR2GRAY); // convert to grayscale - problem is here
Rest of the code is so long so I dont paste it if any one wants it I can add.
Here images that im progressing
TO:
Finally error is:assertion failed (scn == 3 scn == 4) in cvtcolor

Answer 1

Just read the error, please.
According to the docs:
C++: void inRange(InputArray src, InputArray lowerb, InputArray upperb, OutputArray dst)
...
Parameters:
...
dst – output array of the same size as src and CV_8U type.
Your dst image is single-channel. cvtColor with CV_BGR2GRAY expects a BGR image as input.