Slightly better similarity samples

Slight modification of the image_sim_fill_data, that creates the
similarity signature. When the image size is not a multiple of 32, all
cells had size w/32, so the last w%32 pixels were just ignored, and more
importantly it was not symmetric at all when the signature was built
from the other side, which is annoying for my comparison algorithm. So I
changed the cell size (x_inc) from a constant one to
"round(w_left/n_left)", in order to spread the spare pixels (eg to split
42 pixels into 4 cells, it results in 11,10,11,10 instead of
10,10,10,10). With an image of size w with w%32=16, my
rotation-invariant algorithm results in a similarity of
0.951000 with the original version, and 0.999968 with this modification
(apparently lossless jpeg rotation is not perfectly lossless).

Signed-off-by: Klaus Ethgen <Klaus@Ethgen.de>

diff --git a/src/similar.c b/src/similar.c
index 7f51f6c..316dfa1 100644 (file)
--- a/src/similar.c
+++ b/src/similar.c
@@ -169,6 +169,13 @@ void image_sim_alternate_processing(ImageSimilarityData *sd)
 #endif
 }
 
+gint mround(gdouble x)
+{
+       gint ipart = x;
+       gdouble fpart = x-ipart;
+       return (fpart < 0.5 ? ipart : ipart+1);
+}
+
 void image_sim_fill_data(ImageSimilarityData *sd, GdkPixbuf *pixbuf)
 {
        gint w, h;
@@ -182,10 +189,10 @@ void image_sim_fill_data(ImageSimilarityData *sd, GdkPixbuf *pixbuf)
        gint j;
        gint x_inc, y_inc, xy_inc;
        gint xs, ys;
+       gint w_left, h_left;
 
        gboolean x_small = FALSE;       /* if less than 32 w or h, set TRUE */
        gboolean y_small = FALSE;
-
        if (!sd || !pixbuf) return;
 
        w = gdk_pixbuf_get_width(pixbuf);
@@ -197,6 +204,8 @@ void image_sim_fill_data(ImageSimilarityData *sd, GdkPixbuf *pixbuf)
        p_step = has_alpha ? 4 : 3;
        x_inc = w / 32;
        y_inc = h / 32;
+       w_left = w;
+       h_left = h;
 
        if (x_inc < 1)
                {
@@ -209,16 +218,16 @@ void image_sim_fill_data(ImageSimilarityData *sd, GdkPixbuf *pixbuf)
                y_small = TRUE;
                }
 
-       xy_inc = x_inc * y_inc;
-
        j = 0;
 
+       h_left = h;
        for (ys = 0; ys < 32; ys++)
                {
                if (y_small) j = (gdouble)h / 32 * ys;
-
+                       else y_inc = mround((gdouble)h_left/(32-ys));
                i = 0;
 
+               w_left = w;
                for (xs = 0; xs < 32; xs++)
                        {
                        gint x, y;
@@ -227,7 +236,8 @@ void image_sim_fill_data(ImageSimilarityData *sd, GdkPixbuf *pixbuf)
                        guchar *xpos;
 
                        if (x_small) i = (gdouble)w / 32 * xs;
-
+                               else x_inc = mround((gdouble)w_left/(32-xs));
+                       xy_inc = x_inc * y_inc;
                        r = g = b = 0;
                        xpos = pix + (i * p_step);
 
@@ -253,9 +263,11 @@ void image_sim_fill_data(ImageSimilarityData *sd, GdkPixbuf *pixbuf)
                        sd->avg_b[t] = b;
 
                        i += x_inc;
+                       w_left -= x_inc;
                        }
 
                j += y_inc;
+               h_left -= y_inc;
                }
 
        sd->filled = TRUE;