[zbar-commits] push rev [276]: Increase precision of the inverse affine transform in the QR decoder.

[<tte...@us...>]

changeset: 276:f36974fe2b4b
user:      tte...@us...
date:      Thu Dec 09 12:17:27 2010 -0800
details:   http://zbar.hg.sourceforge.net:8000/hgroot/zbar/zbarzbar/rev/f36974fe2b4b
description:
Increase precision of the inverse affine transform in the QR decoder.

For large images, the coefficients of the inverse affine transform did
 not have many significant bits, resulting in unprojected points that
 were too far left and up.
This interacted badly with the code that tries to follow the right and
 bottom edges to locate the lower-right corner of the code area (where
 there is no finder pattern).
This change just performs the intermediate calculations in the
 unprojection with more significant bits; overflow could be a problem
 for very skewed images, but these are unlikely to decode correctly
 anyway.
Fixes issue 3131834:
 http://sourceforge.net/tracker/?func=detail&atid=928516&aid=3131834&group_id=189236

diffstat:

 zbar/qrcode/qrdec.c |  29 ++++++++++++++++++-----------
 1 files changed, 18 insertions(+), 11 deletions(-)

diffs (81 lines):

diff -r c617889f8f73 -r f36974fe2b4b zbar/qrcode/qrdec.c
--- a/zbar/qrcode/qrdec.c	Mon Nov 29 14:48:55 2010 -0800
+++ b/zbar/qrcode/qrdec.c	Thu Dec 09 12:17:27 2010 -0800
@@ -630,11 +630,12 @@
   int x0;
   int y0;
   int res;
+  int ires;
 };
 
 
 static void qr_aff_init(qr_aff *_aff,
- const qr_point _p0,const qr_point _p1,const qr_point _p2,int _res){
+ const qr_point _p0,const qr_point _p1,const qr_point _p2,int _res,int _ires){
   int det;
   int dx1;
   int dy1;
@@ -650,20 +651,23 @@
   _aff->fwd[0][1]=dx2;
   _aff->fwd[1][0]=dy1;
   _aff->fwd[1][1]=dy2;
-  _aff->inv[0][0]=QR_DIVROUND(dy2<<_res,det);
-  _aff->inv[0][1]=QR_DIVROUND(-dx2<<_res,det);
-  _aff->inv[1][0]=QR_DIVROUND(-dy1<<_res,det);
-  _aff->inv[1][1]=QR_DIVROUND(dx1<<_res,det);
+  _aff->inv[0][0]=QR_DIVROUND(dy2<<_res,det>>_ires);
+  _aff->inv[0][1]=QR_DIVROUND(-dx2<<_res,det>>_ires);
+  _aff->inv[1][0]=QR_DIVROUND(-dy1<<_res,det>>_ires);
+  _aff->inv[1][1]=QR_DIVROUND(dx1<<_res,det>>_ires);
   _aff->x0=_p0[0];
   _aff->y0=_p0[1];
   _aff->res=_res;
+  _aff->ires=_ires;
 }
 
 /*Map from the image (at subpel resolution) into the square domain.*/
 static void qr_aff_unproject(qr_point _q,const qr_aff *_aff,
  int _x,int _y){
-  _q[0]=_aff->inv[0][0]*(_x-_aff->x0)+_aff->inv[0][1]*(_y-_aff->y0);
-  _q[1]=_aff->inv[1][0]*(_x-_aff->x0)+_aff->inv[1][1]*(_y-_aff->y0);
+  _q[0]=_aff->inv[0][0]*(_x-_aff->x0)+_aff->inv[0][1]*(_y-_aff->y0)
+   +(1<<_aff->ires-1)>>_aff->ires;
+  _q[1]=_aff->inv[1][0]*(_x-_aff->x0)+_aff->inv[1][1]*(_y-_aff->y0)
+   +(1<<_aff->ires-1)>>_aff->ires;
 }
 
 /*Map from the square domain into the image (at subpel resolution).*/
@@ -1894,10 +1898,10 @@
   if(nc[0]){
     dx=QR_DIVROUND(c[0][0],nc[0]);
     dy=QR_DIVROUND(c[0][1],nc[0]);
-    /*But only if it doesn't make things worse.*/
+    /*But only if it doesn't make things too much worse.*/
     match=qr_alignment_pattern_fetch(p,bestx+dx,besty+dy,_img,_width,_height);
     dist=qr_hamming_dist(match,0x1F8D63F,best_dist+1);
-    if(dist<=best_dist){
+    if(dist<=best_dist+1){
       bestx+=dx;
       besty+=dy;
     }
@@ -3629,6 +3633,7 @@
     qr_finder ur;
     qr_finder dl;
     int       res;
+    int       ires;
     int       ur_version;
     int       dl_version;
     int       fmt_info;
@@ -3641,8 +3646,10 @@
        estimate it there.
       Although it should be the same along both axes, we keep separate
        estimates to account for any remaining projective distortion.*/
-    res=QR_INT_BITS-2-QR_FINDER_SUBPREC-qr_ilog(QR_MAXI(_width,_height)-1);
-    qr_aff_init(&aff,ul.c->pos,ur.c->pos,dl.c->pos,res);
+    ires=qr_ilog(QR_MAXI(_width,_height)-1)+QR_FINDER_SUBPREC;
+    res=QR_INT_BITS-2-ires;
+    ires-=2;
+    qr_aff_init(&aff,ul.c->pos,ur.c->pos,dl.c->pos,res,ires);
     qr_aff_unproject(ur.o,&aff,ur.c->pos[0],ur.c->pos[1]);
     qr_finder_edge_pts_aff_classify(&ur,&aff);
     if(qr_finder_estimate_module_size_and_version(&ur,1<<res,1<<res)<0)continue;