how to make the program wait until I move the chessboard - c++

Question

I want to calibrate my stereo camera so, I am trying to capture 10 images for a chessboard from the right and the left camera .
what the code should do:
capture 10 images of a chessboard from the right and the left camera.The program saves the two images if both contain a clear corner points. The program should wait 20 frames for me to change the position of the chessboard.
what is happening :
it capture the 10 good images and saves them but, it does not wait for me to change the position of the chessboard
this is my code:
int captureImages_stereoCal()
{
CvCapture* captureL = cvCreateCameraCapture(1);
assert(captureL);
waitKey(10000);
CvCapture* captureR = cvCreateCameraCapture(2);
assert(captureR);
waitKey(10000);
/*Mat imageL ;
Mat imageR*/ ;
int nx=8 , nh=5;
int frame=0;
int s =1;
int ss;
CvPoint2D32f* cornersL = new CvPoint2D32f[nx*nh];
int corner_countL;
CvPoint2D32f* cornersR = new CvPoint2D32f[nx*nh];
int corner_countR;
IplImage *imageL=cvQueryFrame(captureL);
IplImage *gray_imageL=cvCreateImage(cvGetSize(imageL),8,1);
IplImage *CimageL=cvCreateImage(cvGetSize(imageL),32,3);
IplImage *imageR=cvQueryFrame(captureR);
IplImage *gray_imageR=cvCreateImage(cvGetSize(imageR),8,1);
IplImage *CimageR=cvCreateImage(cvGetSize(imageL),32,3);
const int board_dt=20;
while(s<=12)
{
if(frame++ % board_dt == 0)
{
string Result;
ostringstream convert;
ss=s-2;
convert << ss;
Result = convert.str();
//n=(char)s;
//waitKey(1000);
//Left -----------------------------------------------------------------------------------------------------------
string nameL="L.jpg";
//Find chessboard corners:
int foundL = cvFindChessboardCorners(imageL, Size(nx,nh), cornersL, &corner_countL,CV_CALIB_CB_ADAPTIVE_THRESH | CV_CALIB_CB_FILTER_QUADS);
//Get Subpixel accuracy on those corners
cvCvtColor(imageL, gray_imageL, CV_BGR2GRAY);
cvFindCornerSubPix(gray_imageL, cornersL, corner_countL,cvSize(11,11),cvSize(-1,-1), cvTermCriteria(CV_TERMCRIT_EPS+CV_TERMCRIT_ITER, 30, 0.1 ));
//Draw it
Mat MimageL(imageL);
CimageL=imageL;
cvDrawChessboardCorners(CimageL, Size(nx,nh), cornersL,corner_countL, foundL);
//Right -----------------------------------------------------------------------------------------------
string nameR="R.jpg";
//Find chessboard corners:
int foundR = cvFindChessboardCorners(imageR, Size(nx,nh), cornersR, &corner_countR,CV_CALIB_CB_ADAPTIVE_THRESH | CV_CALIB_CB_FILTER_QUADS);
//Get Subpixel accuracy on those corners
cvCvtColor(imageR, gray_imageR, CV_BGR2GRAY);
cvFindCornerSubPix(gray_imageR, cornersR, corner_countR,cvSize(11,11),cvSize(-1,-1), cvTermCriteria(CV_TERMCRIT_EPS+CV_TERMCRIT_ITER, 30, 0.1 ));
//Draw it
Mat MimageR(imageR);
CimageR=imageR;
cvDrawChessboardCorners(CimageR, Size(nx,nh), cornersR,corner_countR, foundR);
cvShowImage( "CalibrationL", CimageL );
cvShowImage( "CalibrationR", CimageR );
if(s>2)
{
if((corner_countL==(nx*nh)) && (corner_countR==(nx*nh)) )
{
nameL.insert(1,Result);
imwrite(nameL,MimageL);
nameR.insert(1,Result);
imwrite(nameR,MimageR);
s++;
}
}
int c = cvWaitKey(15);
if(c == 'p')
{
c = 0;
while(c != 'p' && c != 27)
{
c = cvWaitKey(250);
}
}
if(c == 27)
return 0;
imageL = cvQueryFrame(captureL);
imageR = cvQueryFrame(captureR);
if(s<3)
s++;
}// frame++ end
} // while end
return 0;
}
Also , after it draws the corners it saves the image with the corners drawn on it. I want to save the images with out any changes.

Answer 1

If I understand the problem correctly, it's because you're using a post-increment on your if-statement conditional:
if(frame++ % board_dt == 0)
You initialize frame to be 0 above, so on the 1st call, the if-statement is effectively testing (0 % 20) == 0, which is true.
You can change the if-statement to be a pre-increment, e.g.
if(++frame % board_dt == 0) to get the behavior you are looking for