Question

I’m trying to include OpenCV (version 2.3.1) in a project I’m working on. A camera is sending my program (in Microsoft Visual C++ 2008 on a Windows 7 64-bit machine) an image stream, which the program stores in an unsigned 8-bit integer buffer. I would like to display this stream in a window using OpenCV. Right now, I can’t seem to get any images to display in my OpenCV windows, so I’m not using my image stream yet; just a JPEG file.

First I declare my window:

namedWindow( "Window", CV_WINDOW_AUTOSIZE );

Then I try to fill it:

char* imgName = "C:\...\Jellyfish.jpg";
Mat imgMat = imread(imgName, 1);
if(imgMat.data)
{
     imshow( "Window", imgMat );
}

When my program gets to the point where the window gets declared, a tiny gray window appears. When it reaches the point where it is supposed to display the image, the window’s dimensions change to that of the image (I’ve tested this with different images) but the inside of the window remains a plain gray box.

What is causing this strange error? The program obviously found the image, or it would not have been able to change its dimensions correctly.

Answer 1

You need to add waitKey(2) function call after the imshow.

From OpenCV documentation for waitKey:

This function is the only method in HighGUI that can fetch and handle
events, so it needs to be called periodically for normal event
processing unless HighGUI is used within an environment that takes
care of event processing.

Without this function Windows is unable to handle PAINT event and redraw your window.