Convert OGRE::Image to cv::Mat - c++

Question

I am new to OGRE library. I have a human model in OGRE, I get the projection of the model in 'orginalImage' variable. I would like to perform some image processing using openCV. So I am trying to achieve OGRE::Image to cv::Mat conversion.
Ogre::Image orginalImage = get2dProjection();
//This is an attempt to convert the image
cv::Mat destinationImage(orginalImage.getHeight(), orginalImage.getWidth(), CV_8UC3, orginalImage.getData());
imwrite("out.png", destinationImage);
I get following error:
realloc(): invalid pointer: 0x00007f9e2ca13840 ***
On the similar note, I tried following as my second attempt
cv::Mat cvtImgOGRE2MAT(Ogre::Image imgIn) {
//Result image intialisation:
int imgHeight = imgIn.getHeight();
int imgWidth = imgIn.getWidth();
cv::Mat imgOut(imgHeight, imgWidth, CV_32FC1);
Ogre::ColourValue color;
float gray;
cout << "Converting " << endl;
for(int r = 0; r < imgHeight; r++){
for(int c = 0; c < imgWidth; c++){
color = imgIn.getColourAt(r,c,0);
gray = 0.2126 * color.r + 0.7152 * color.g + 0.0722 * color.b;
imgOut.at<float>(r,c) = gray;
}
}
return imgOut;
}
I get same error when I do one of the following:
imshow("asdfasd", imgOut);
imwrite("asdfasd.png", imgOut);

Answer 1

unfortunately I have no experience with OGRE, so I can just talk about OpenCV and what I've seen in Ogre documentation and poster's comments.
The first thing to mention is that the Ogre image' PixelFormat is PF_BYTE_RGBA (from comments) which is (according to OGRE documentation) a 4 byte pixel format, so the cv::Mat type should be CV_8UC4 if image data should be given by pointer. In addition, openCV best supports BGR images, so a color conversion might be best to save/display.
please try:
Ogre::Image orginalImage = get2dProjection();
//This is an attempt to convert the image
cv::Mat destinationImage(orginalImage.getHeight(), orginalImage.getWidth(), CV_8UC4, orginalImage.getData());
cv::Mat resultBGR;
cv::cvtColor(destinationImage, resultBGR, CV_RGBA2BGR);
imwrite("out.png", resultBGR);
in your second example I wondered what is wrong there, until I saw color = imgIn.getColourAt(r,c,0); which might be wrong since most image APIs use .getPixel(x,y) so I confirmed that this is the same for OGRE. Please try this:
cv::Mat cvtImgOGRE2MAT(Ogre::Image imgIn)
{
//Result image intialisation:
int imgHeight = imgIn.getHeight();
int imgWidth = imgIn.getWidth();
cv::Mat imgOut(imgHeight, imgWidth, CV_32FC1);
Ogre::ColourValue color;
float gray;
cout << "Converting " << endl;
for(int r = 0; r < imgHeight; r++)
{
for(int c = 0; c < imgWidth; c++)
{
// next line was changed
color = imgIn.getColourAt(c,r,0);
gray = 0.2126 * color.r + 0.7152 * color.g + 0.0722 * color.b;
// this access is right
imgOut.at<float>(r,c) = gray;
}
}
return imgOut;
// depending of what you want to do with the image, "float" Mat type assumes what image intensity values are within 0..1 (displaying) or 0..255 (imwrite)
}
if you still get realloc errors, can you please try to find the exact line of code where it happens?
One thing I didnt consider yet is the real memory layout of OGRE images. It might be possible that they use some kind of aligned memory, where each pixel-row is aligned to have a memory size as a multiple of 4 or 16 or sth. (which might be more efficient, e.g. to use SSE instructions or sth.) If that is the case, you can't use the first method but you would have to change it to cv::Mat destinationImage(orginalImage.getHeight(), orginalImage.getWidth(), CV_8UC4, orginalImage.getData(), STEPSIZE); where STEPSIZE is the number of BYTES for each pixel ROW! But the second version should work then!