libfprint/libfprint/nbis/mindtct/chaincod.c

/*******************************************************************************

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*******************************************************************************/


/***********************************************************************
      LIBRARY: LFS - NIST Latent Fingerprint System

      FILE:    CHAINCODE.C
      AUTHOR:  Michael D. Garris
      DATE:    05/11/1999

      Contains routines responsible for generating and manipulating
      chain codes as part of the NIST Latent Fingerprint System (LFS).

***********************************************************************
               ROUTINES:
                        chain_code_loop()
                        is_chain_clockwise()
***********************************************************************/

#include <stdio.h>
#include <lfs.h>

/*************************************************************************
**************************************************************************
#cat: chain_code_loop - Converts a feature's contour points into an
#cat:            8-connected chain code vector.  This encoding represents
#cat:            the direction taken between each adjacent point in the
#cat:            contour.  Chain codes may be used for many purposes, such
#cat:            as computing the perimeter or area of an object, and they
#cat:            may be used in object detection and recognition.

   Input:
      contour_x - x-coord list for feature's contour points
      contour_y - y-coord list for feature's contour points
      ncontour  - number of points in contour
   Output:
      ochain    - resulting vector of chain codes
      onchain   - number of codes in chain
                  (same as number of points in contour)
   Return Code:
      Zero      - chain code successful derived
      Negative  - system error
**************************************************************************/
int chain_code_loop(int **ochain, int *onchain,
               const int *contour_x, const int *contour_y, const int ncontour)
{
   int *chain;
   int i, j, dx, dy;

   /* If we don't have at least 3 points in the contour ... */
   if(ncontour <= 3){
      /* Then we don't have a loop, so set chain length to 0 */
      /* and return without any allocations.                 */
      *onchain = 0;
      return(0);
   }

   /* Allocate chain code vector.  It will be the same length as the */
   /* number of points in the contour.  There will be one chain code */
   /* between each point on the contour including a code between the */
   /* last to the first point on the contour (completing the loop).  */
   chain = (int *)malloc(ncontour * sizeof(int));
   /* If the allocation fails ... */
   if(chain == (int *)NULL){
      fprintf(stderr, "ERROR : chain_code_loop : malloc : chain\n");
      return(-170);
   }

   /* For each neighboring point in the list (with "i" pointing to the */
   /* previous neighbor and "j" pointing to the next neighbor...       */
   for(i = 0, j=1; i < ncontour-1; i++, j++){
      /* Compute delta in X between neighbors. */
      dx = contour_x[j] - contour_x[i];
      /* Compute delta in Y between neighbors. */
      dy = contour_y[j] - contour_y[i];
      /* Derive chain code index from neighbor deltas.                  */
      /* The deltas are on the range [-1..1], so to use them as indices */
      /* into the code list, they must first be incremented by one.     */
      chain[i] = *(g_chaincodes_nbr8+((dy+1)*NBR8_DIM)+dx+1);
   }

   /* Now derive chain code between last and first points in the */
   /* contour list.                                              */
   dx = contour_x[0] - contour_x[i];
   dy = contour_y[0] - contour_y[i];
   chain[i] = *(g_chaincodes_nbr8+((dy+1)*NBR8_DIM)+dx+1);

   /* Store results to the output pointers. */
   *ochain = chain;
   *onchain = ncontour;

   /* Return normally. */
   return(0);
}

/*************************************************************************
**************************************************************************
#cat: is_chain_clockwise - Takes an 8-connected chain code vector and
#cat:            determines if the codes are ordered clockwise or
#cat:            counter-clockwise.
#cat:            The routine also requires a default return value be
#cat:            specified in the case the the routine is not able to
#cat:            definitively determine the chains direction.  This allows
#cat:            the default response to be application-specific.

   Input:
      chain       - chain code vector
      nchain      - number of codes in chain
      default_ret - default return code (used when we can't tell the order)
   Return Code:
      TRUE      - chain determined to be ordered clockwise
      FALSE     - chain determined to be ordered counter-clockwise
      Default   - could not determine the order of the chain
**************************************************************************/
int is_chain_clockwise(const int *chain, const int nchain,
                       const int default_ret)
{
   int i, j, d, sum;

   /* Initialize turn-accumulator to 0. */
   sum = 0;

   /* Foreach neighboring code in chain, compute the difference in  */
   /* direction and accumulate.  Left-hand turns increment, whereas */
   /* right-hand decrement.                                         */
   for(i = 0, j =1; i < nchain-1; i++, j++){
      /* Compute delta in neighbor direction. */
      d = chain[j] - chain[i];
      /* Make the delta the "inner" distance. */
      /* If delta >= 4, for example if chain_i==2 and chain_j==7 (which   */
      /* means the contour went from a step up to step down-to-the-right) */
      /* then 5=(7-2) which is >=4, so -3=(5-8) which means that the      */
      /* change in direction is a righ-hand turn of 3 units).             */
      if(d >= 4)
         d -= 8;
      /* If delta <= -4, for example if chain_i==7 and chain_j==2 (which  */
      /* means the contour went from a step down-to-the-right to step up) */
      /* then -5=(2-7) which is <=-4, so 3=(-5+8) which means that the    */
      /* change in direction is a left-hand turn of 3 units).             */
      else if (d <= -4)
         d += 8;

      /* The delta direction is then accumulated. */
      sum += d;
   }

   /* Now we need to add in the final delta direction between the last */
   /* and first codes in the chain.                                    */
   d = chain[0] - chain[i];
   if(d >= 4)
      d -= 8;
   else if (d <= -4)
      d += 8;
   sum += d;

   /* If the final turn_accumulator == 0, then we CAN'T TELL the       */
   /* direction of the chain code, so return the default return value. */
   if(sum == 0)
      return(default_ret);
   /* Otherwise, if the final turn-accumulator is positive ... */
   else if(sum > 0)
      /* Then we had a greater amount of left-hand turns than right-hand     */
      /* turns, so the chain is in COUNTER-CLOCKWISE order, so return FALSE. */
      return(FALSE);
   /* Otherwise, the final turn-accumulator is negative ... */
   else
      /* So we had a greater amount of right-hand turns than left-hand  */
      /* turns, so the chain is in CLOCKWISE order, so return TRUE.     */
      return(TRUE);
}