Colour conversion not working in opencv? - c

Question

#include<highgui.h>
#include<cxcore.h>
#include<cv.h>
#include<stdio.h>
#include<stdlib.h>
int main(int argc, char* argv[])
{
IplImage* img = cvLoadImage("hello.jpg", CV_WINDOW_FULLSCREEN );
int *img_data;
img_data = malloc(sizeof(*img_data)*img->height*img->width*img->nChannels);
if (!img)
{
printf("Image can NOT Load!!!\n");
return 1;
}
cvNamedWindow("myfirstwindow", CV_WINDOW_FREERATIO );
cvShowImage("myfirstwindow", img);
printf("Height: %d\nwidth: %d\nnchannels:%d\n",img->height,img->width,img->nChannels);
cvCvtColor(img,img_data,CV_RGB2XYZ);
cvWaitKey(0);
cvReleaseImage(&img);
return 0;
}
In this program I am trying to convert RGB color model to XYZ color model using function cvCvtColor. And i am getting error shown below:
OpenCV Error: Bad argument (Unknown array type) in cvarrToMat, file
/build/buildd/opencv-2.3.1/modules/core/src/matrix.cpp, line 646
terminate called after throwing an instance of 'cv::Exception'
what(): /build/buildd/opencv-2.3.1/modules/core/src/matrix.cpp:646:
error: (-5) Unknown array type in function cvarrToMat
Any help or suggestion will be greatly appreciated. Thank you.

Answer 1

do yourself (and us) a favour, and switch to the c++ api.
the old c-api is no longer developed, and only around for maintenance, don't write any new code in that !
#include "opencv2/highgui/highgui.hpp"
#include "opencv2/imgproc/imgproc.hpp"
#include "opencv2/core/core.hpp"
using namespace cv;
int main()
{
namedWindow("myfirstwindow", CV_WINDOW_FREERATIO );
Mat img = imread("hello.jpg", CV_IMAGE_LOAD_COLOR);
imshow("myfirstwindow",img);
Mat hsv;
cvtColor(img,hsv,CV_RGB2HSV);
waitKey(0);
return 0;
}

Answer 2

You are passing enum value CV_WINDOW_FULLSCREEN which is meant for specifying the property of window when calling cvNamedWindow. For image loading, it should be some enum value like CV_LOAD_IMAGE_COLOR or CV_LOAD_IMAGE_GRAYSCALE.
But your code is not crashing here because fortunately, the integral value of CV_WINDOW_FULLSCREEN and CV_LOAD_IMAGE_COLOR is same, i.e. 1, so basically these enum values are equal.
The real cause of error in the code is you are passing raw int* to the function cvCvtColor. All opencv C functions expect IplImage* as arguments. The following line is causing the error.
cvCvtColor(img,img_data,CV_RGB2XYZ);
You might want to do something like this:
int main(int argc, char* argv[])
{
IplImage* img = cvLoadImage("hello.jpg", CV_LOAD_IMAGE_COLOR);
IplImage *img_data;
img_data = cvCreateImage(cvGetSize(img), img->depth, img->nChannels);
if (!img)
{
printf("Image can NOT Load!!!\n");
return 1;
}
cvNamedWindow("myfirstwindow", CV_WINDOW_FREERATIO );
cvShowImage("myfirstwindow", img);
printf("Height: %d\nwidth: %d\nnchannels:%d\n",img->height,img->width,img->nChannels);
cvCvtColor(img,img_data,CV_RGB2XYZ);
cvWaitKey(0);
cvReleaseImage(&img);
cvReleaseImage(&img_data);
return 0;
}

Answer 3

You need to pass CV_LOAD_IMAGE_COLOR to the function cvLoadImage(), which will load color image.