Question

In my C/C++ program, I’m using OpenCV to capture images from my webcam. The camera (Logitech QuickCam IM) can capture at resolutions 320×240, 640×480 and 1280×960. But, for some strange reason, OpenCV gives me images of resolution 320×240 only. Calls to change the resolution using cvSetCaptureProperty() with other resolution values just don’t work. How do I capture images with the other resolutions possible with my webcam?

Answer 1

There doesn’t seem to be a solution. The resolution can be increased to 640×480 using this hack shared by lifebelt77. Here are the details reproduced:

Add to highgui.h:

#define CV_CAP_PROP_DIALOG_DISPLAY 8 #define CV_CAP_PROP_DIALOG_FORMAT 9 #define CV_CAP_PROP_DIALOG_SOURCE 10 #define CV_CAP_PROP_DIALOG_COMPRESSION 11 #define CV_CAP_PROP_FRAME_WIDTH_HEIGHT 12 

Add the function icvSetPropertyCAM_VFW to cvcap.cpp:

static int icvSetPropertyCAM_VFW( CvCaptureCAM_VFW* capture, int property_id, double value ) {     int result = -1;     CAPSTATUS capstat;     CAPTUREPARMS capparam;     BITMAPINFO btmp;      switch( property_id )     {         case CV_CAP_PROP_DIALOG_DISPLAY:             result = capDlgVideoDisplay(capture->capWnd);             //SendMessage(capture->capWnd,WM_CAP_DLG_VIDEODISPLAY,0,0);             break;          case CV_CAP_PROP_DIALOG_FORMAT:             result = capDlgVideoFormat(capture->capWnd);             //SendMessage(capture->capWnd,WM_CAP_DLG_VIDEOFORMAT,0,0);             break;          case CV_CAP_PROP_DIALOG_SOURCE:             result = capDlgVideoSource(capture->capWnd);             //SendMessage(capture->capWnd,WM_CAP_DLG_VIDEOSOURCE,0,0);             break;          case CV_CAP_PROP_DIALOG_COMPRESSION:             result = capDlgVideoCompression(capture->capWnd);             break;          case CV_CAP_PROP_FRAME_WIDTH_HEIGHT:             capGetVideoFormat(capture->capWnd, &btmp, sizeof(BITMAPINFO));             btmp.bmiHeader.biWidth = floor(value/1000);             btmp.bmiHeader.biHeight = value-floor(value/1000)*1000;             btmp.bmiHeader.biSizeImage = btmp.bmiHeader.biHeight *             btmp.bmiHeader.biWidth * btmp.bmiHeader.biPlanes *             btmp.bmiHeader.biBitCount / 8;             capSetVideoFormat(capture->capWnd, &btmp, sizeof(BITMAPINFO));             break;          default:             break;     }      return result; } 

and edit captureCAM_VFW_vtable as following:

static CvCaptureVTable captureCAM_VFW_vtable = { 6, (CvCaptureCloseFunc)icvCloseCAM_VFW, (CvCaptureGrabFrameFunc)icvGrabFrameCAM_VFW, (CvCaptureRetrieveFrameFunc)icvRetrieveFrameCAM_VFW, (CvCaptureGetPropertyFunc)icvGetPropertyCAM_VFW, (CvCaptureSetPropertyFunc)icvSetPropertyCAM_VFW, // was NULL (CvCaptureGetDescriptionFunc)0 }; 

Now rebuilt highgui.dll.