image pixels addition and subtraction. please help!!

[dolly_olaide]

Hi.

I am trying to implement adding then subtracting images but I can't seem to get it right. My thoughts are to load the image. add the pixel values. Firstly, I can get the pixel location but I DON'T KNOW HOW TO DISPLAY THE PIXEL VALUES from the pixel location.
Secondly, I generate a new blank image using the cvCreateImage opencv function. But I don't know how to get the pixel values from the pixel location, add the pixel values together then put it in the blank image I created. I can't use the cvAdd or any opencv functions. Similarly, the same issues apply for the subtraction of the images. Please help.

using namespace std;
typedef unsigned char uchar;


int main (int argc, char *argv[])
{
	
	// Declare the variables
	IplImage *image, *img;
	int height, width;
	int i, j;
	uchar** ImageData;
	uchar* data, data2;
	double mean, std_dev;
	CvScalar sc, s;
	

	cvNamedWindow("Ass1", 1);
	img = cvLoadImage(argv[1],1);

	//convert to greyscale image
	image = cvCreateImage(cvGetSize(img), IPL_DEPTH_8U, 1);
	cvCvtColor(img, image,CV_BGR2GRAY);

	cvShowImage("Ass1", image);
	cvWaitKey(0);


	//Calculate the height and width of the image
	height = image->height;
	width = image->width;
	data  = (uchar *)image->imageData;
	
	//Add the pixels together
	IplImage *add;
	add = cvCreateImage( cvGetSize(img), IPL_DEPTH_8U, 1 );
	//data2 = (uchar*)add->imageData;
	//cvGetRawData(add, (uchar**)&data2);
	double maxi = 255;
	for (int x = 0; x < height; x++)
	{
	for (int y = 0; y < width; y++)
	{

		data[((height * y) + x)] = data[((height * y) + x)] + data[((height * y) + x)];
		
		if (data[((height * y) + x)] < maxi)
			data[((height * y) + x)] = maxi;

	}
	}

	cvReleaseImage(&image);
	cvDestroyWindow("Ass1");

	return 0;

}