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Your program has a couple of issues. First of all <code>imgColor</code> is not declared, you'll need: <pre><code>IplImage* imgColor = cvCreateImage(cvSize(640, 480), IPL_DEPTH_8U, 3); </code></pre> Also, on: <pre><code>void changeColor(int pos) { cvSet(imgColor, CV_RGB(red, green, blue), NULL); } </code></pre> you can't access neither <code>red</code>, nor <code>green</code>, nor <code>blue</code> here, for they are local to main. I take it this is just a concept proof example, let's declare these global. Now onto why no windows is displayed. There are two reasons: <ol> <li>That may sound obvious, but well, main is returning, your program is simply exiting. As sgar91 already pointed out, you'll need <code>cvWaitKey(0);</code> at the end of main so you program can hold there processing gui events.</li> <li>That also might sound obvious, but you haven't actually instructed OpenCV to show anything. You'll need <code>cvShowImage("ColorSelector", imgColor);</code>, this will trigger events for window painting inside OpenCV;</li> </ol> The following quick and dirty example works fine and I'm able to select the color which is displayed on the window. <pre><code>#include <cstdio> #include "cv.h" #include "highgui.h" int red, blue, green; IplImage* imgColor = cvCreateImage(cvSize(640, 480), IPL_DEPTH_8U, 3); void changeColor(int pos) { cvSet(imgColor, CV_RGB(red, green, blue), NULL); cvShowImage("ColorSelector", imgColor); } int main() { // cvNamedWindow("DrawArea", 0); //area for inputting digits cvNamedWindow("ColorSelector", 0); //area for selecting colour of input cvShowImage("ColorSelector", imgColor); cvCreateTrackbar("Red", "ColorSelector", &red, 255, &changeColor); cvCreateTrackbar("Green", "ColorSelector", &green, 255, &changeColor); cvCreateTrackbar("Blue", "ColorSelector", &blue, 255, &changeColor); // cvSetMouseCallback("Demo", &on_mouse, 0); cvWaitKey(0); } </code></pre>
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