Fixes to the scale function so that edges are handled by extending the edges

of the image with the value at the endpoint.  This avoids ringing near edges
for some images.

diff --git a/image.c b/image.c
index 8c6149d72dca75f11704a67a04ae1aaa6f7fa147..1537e9ddc298e6611ec068155e980b112ec00601 100644 (file)
--- a/image.c
+++ b/image.c
@@ -948,7 +948,7 @@ i_scaleaxis(i_img *im, float Value, int Axis) {
   
   new_img = i_img_empty_ch(NULL, hsize, vsize, im->channels);
   
-  /* 1.5 is a magic number, setting it to 2 will cause rather blurred images */
+  /* 1.4 is a magic number, setting it to 2 will cause rather blurred images */
   LanczosWidthFactor = (Value >= 1) ? 1 : (int) (1.4/Value); 
   lMax = LanczosWidthFactor << 1;
   
@@ -982,9 +982,15 @@ i_scaleaxis(i_img *im, float Value, int Axis) {
       
       for (i=0; i<iEnd; i++) {
        for (k=0; k<im->channels; k++) PictureValue[k] = 0.0;
-       for (l=0; l < lMax; l++) {
-         i_gpix(im, T+l+1,      i, &val1);
-         i_gpix(im, T-lMax+l+1, i, &val2);
+       for (l=0; l<lMax; l++) {
+         int mx = T-lMax+l+1;
+         int Mx = T+l+1;
+         mx = (mx < 0) ? 0 : mx;
+         Mx = (Mx >= im->xsize) ? im->xsize-1 : Mx;
+         
+         i_gpix(im, Mx, i, &val1);
+         i_gpix(im, mx, i, &val2);
+         
          for (k=0; k<im->channels; k++) {
            PictureValue[k] += l1[l]        * val1.channel[k];
            PictureValue[k] += l0[lMax-l-1] * val2.channel[k];
@@ -1002,15 +1008,20 @@ i_scaleaxis(i_img *im, float Value, int Axis) {
       for (i=0; i<iEnd; i++) {
        for (k=0; k<im->channels; k++) PictureValue[k] = 0.0;
        for (l=0; l < lMax; l++) {
-         i_gpix(im, i, T+l+1, &val1);
-         i_gpix(im, i, T-lMax+l+1, &val2);
+         int mx = T-lMax+l+1;
+         int Mx = T+l+1;
+         mx = (mx < 0) ? 0 : mx;
+         Mx = (Mx >= im->ysize) ? im->ysize-1 : Mx;
+
+         i_gpix(im, i, Mx, &val1);
+         i_gpix(im, i, mx, &val2);
          for (k=0; k<im->channels; k++) {
-           PictureValue[k] += l1[l] * val1.channel[k];
+           PictureValue[k] += l1[l]        * val1.channel[k];
            PictureValue[k] += l0[lMax-l-1] * val2.channel[k]; 
          }
        }
        for (k=0; k<im->channels; k++) {
-         psave = (short)( PictureValue[k] / LanczosWidthFactor);
+         psave = (short)(0.5+(PictureValue[k] / LanczosWidthFactor));
          val.channel[k] = minmax(0, 255, psave);
        }
        i_ppix(new_img, i, j, &val);
@@ -1332,6 +1343,7 @@ i_gpix_d(i_img *im, int x, int y, i_color *val) {
        val->channel[ch]=im->idata[(x+y*im->xsize)*im->channels+ch];
     return 0;
   }
+  for(ch=0;ch<im->channels;ch++) val->channel[ch] = 0;
   return -1; /* error was cliped */
 }