void invert_image( IplImage* source, IplImage* result )
{
    //+ TO DO:  Write code to invert all points in the source image (i.e. for each channel for each pixel in the result
    //        image the value should be 255 less the corresponding value in the source image).
    int width_step=source->widthStep;
    int pixel_step=source->widthStep/source->width;
    int number_channels=source->nChannels;
    cvZero( result );
    unsigned char white_pixel[4] = {255,255,255,0};
    int row=0,col=0;

    for (row=0; row < result->height; row++)
        for (col=0; col < result->width; col++)
        {
            unsigned char* curr_point = GETPIXELPTRMACRO( source, col, row, width_step, pixel_step );
            char pixel[4]={curr_point[RED_CH]-255,curr_point[GREEN_CH]-255,curr_point[BLUE_CH]-255};
            PUTPIXELMACRO( result, col, row, white_pixel, width_step, pixel_step, number_channels );

        }
}