/***************************************************************************
 * Func: average_shrink                                                    *
 *                                                                         *
 * Desc: Reduces an image using pixel averages                             *
 *                                                                         *
 * Params: source - pointer to image in memory                             *
 *         cols - number of columns in image                               *
 *         rows - number of rows in image                                  *
 *         filename - name of output file                                  *
 *         side - width of block                                           *
 ***************************************************************************/

void average_shrink(image_ptr source, int cols, int rows, char *filename,
		 int side)
    {
    int x, y, i;               /* image loop variables */
    int index;                 /* image index */
    FILE *fp;                  /* output file pointer */
    int *window;               /* window for block samples */
    int wsize;                 /* number of elements in block */
    unsigned char *line_buff;  /* storage for line */
    unsigned long sourcebase;  /* base address in source image */
    unsigned long sourceadd;   /* sourcebase plus a column offset */
    int winx, winy;            /* x and y indices in image window */
    int new_rows;              /* number of rows in new output image */
    int new_cols;              /* number of columns in new output image */
    int new_pixel;             /* newly generated pixel for output image */
    int windex;                /* image window index */

    if((fp=fopen(filename, "wb")) == NULL)
	{
	printf("Unable to open %s for output\n",filename);
	exit(1);
	}

    wsize = side * side;
    new_rows = rows/side;
    new_cols = cols/side;

    /* allocate memory for storage */
    window = malloc(wsize * sizeof(int));
    line_buff = (unsigned char *) malloc(new_cols);

    fprintf(fp, "P5\n%d %d\n255\n", new_cols, new_rows); /* print out header */

    for(y=0; y<new_rows; y++)
	{
	sourcebase=((unsigned long) cols) * side * y;
	index=0;
	for(x=0; x<new_cols; x++)
	   {
	   windex=0;
	   for(winy=0; winy<side; winy++)
	       for(winx=0; winx<side; winx++)
		  {
		  sourceadd=sourcebase+winx+winy*cols;
		  window[windex++] = (int) source[sourceadd];
		  }
	   new_pixel = average(window, wsize);
	   line_buff[index++]=(unsigned char) new_pixel;
	   sourcebase+=side;
	   } /* for x */
	 fwrite(line_buff, 1, new_cols, fp);
    } /* for y */
    free(window);
    }

/***************************************************************************
 * Func: average                                                           *
 *                                                                         *
 * Description: calculates the average of an array of numbers              *
 *                                                                         *
 * Params: window - array of pixel values to average                       *
 *         wsize - number of elements in the array                         *
 *                                                                         *
 * Returns: the average of the numbers in the array                        *
 ***************************************************************************/

int average(int *window, int wsize)
    {
    int i;
    unsigned sum;

    sum = 0;
    for(i=0; i<wsize; i++)
	 sum += window[i];
    return (sum/wsize);
    }