diff --git a/ANNOUNCE b/ANNOUNCE
index 909036e5b..ec5b38fb8 100644
--- a/ANNOUNCE
+++ b/ANNOUNCE
@@ -74,6 +74,10 @@ Version 1.5.6beta06 [October 14, 2011]
   Removed two redundant tests for unitialized row.
   Fixed a relatively harmless memory overwrite in compressed text writing
     with a 1 byte zlib buffer.
+  Fixes for multiple calls to png_read_update_info. These fixes attend to
+    most of the errors revealed in pngvalid, however doing the gamma work
+    twice results in inaccuracies that can't be easily fixed.  There is now
+    a warning in the code if this is going to happen.
 
 Send comments/corrections/commendations to png-mng-implement at lists.sf.net:
 (subscription required; visit
diff --git a/CHANGES b/CHANGES
index 7c414c00a..dd7967ab2 100644
--- a/CHANGES
+++ b/CHANGES
@@ -3635,6 +3635,10 @@ Version 1.5.6beta06 [October 14, 2011]
   Removed two redundant tests for unitialized row.
   Fixed a relatively harmless memory overwrite in compressed text writing
     with a 1 byte zlib buffer.
+  Fixes for multiple calls to png_read_update_info. These fixes attend to
+    most of the errors revealed in pngvalid, however doing the gamma work
+    twice results in inaccuracies that can't be easily fixed.  There is now
+    a warning in the code if this is going to happen.
 
 Send comments/corrections/commendations to png-mng-implement at lists.sf.net
 (subscription required; visit
diff --git a/png.c b/png.c
index 0a96d0d8c..d5d7adbc7 100644
--- a/png.c
+++ b/png.c
@@ -645,13 +645,13 @@ png_get_copyright(png_const_structp png_ptr)
 #else
 #  ifdef __STDC__
    return PNG_STRING_NEWLINE \
-     "libpng version 1.5.6beta06 - October 12, 2011" PNG_STRING_NEWLINE \
+     "libpng version 1.5.6beta06 - October 14, 2011" PNG_STRING_NEWLINE \
      "Copyright (c) 1998-2011 Glenn Randers-Pehrson" PNG_STRING_NEWLINE \
      "Copyright (c) 1996-1997 Andreas Dilger" PNG_STRING_NEWLINE \
      "Copyright (c) 1995-1996 Guy Eric Schalnat, Group 42, Inc." \
      PNG_STRING_NEWLINE;
 #  else
-      return "libpng version 1.5.6beta06 - October 12, 2011\
+      return "libpng version 1.5.6beta06 - October 14, 2011\
       Copyright (c) 1998-2011 Glenn Randers-Pehrson\
       Copyright (c) 1996-1997 Andreas Dilger\
       Copyright (c) 1995-1996 Guy Eric Schalnat, Group 42, Inc.";
@@ -2663,6 +2663,60 @@ png_build_8bit_table(png_structp png_ptr, png_bytepp ptable,
       table[i] = (png_byte)i;
 }
 
+/* Used from png_read_destroy and below to release the memory used by the gamma
+ * tables.
+ */
+void /* PRIVATE */
+png_destroy_gamma_table(png_structp png_ptr)
+{
+   png_free(png_ptr, png_ptr->gamma_table);
+   png_ptr->gamma_table = NULL;
+
+   if (png_ptr->gamma_16_table != NULL)
+   {
+      int i;
+      int istop = (1 << (8 - png_ptr->gamma_shift));
+      for (i = 0; i < istop; i++)
+      {
+         png_free(png_ptr, png_ptr->gamma_16_table[i]);
+      }
+   png_free(png_ptr, png_ptr->gamma_16_table);
+   png_ptr->gamma_16_table = NULL;
+   }
+
+#if defined(PNG_READ_BACKGROUND_SUPPORTED) || \
+   defined(PNG_READ_ALPHA_MODE_SUPPORTED) || \
+   defined(PNG_READ_RGB_TO_GRAY_SUPPORTED)
+   png_free(png_ptr, png_ptr->gamma_from_1);
+   png_ptr->gamma_from_1 = NULL;
+   png_free(png_ptr, png_ptr->gamma_to_1);
+   png_ptr->gamma_to_1 = NULL;
+
+   if (png_ptr->gamma_16_from_1 != NULL)
+   {
+      int i;
+      int istop = (1 << (8 - png_ptr->gamma_shift));
+      for (i = 0; i < istop; i++)
+      {
+         png_free(png_ptr, png_ptr->gamma_16_from_1[i]);
+      }
+   png_free(png_ptr, png_ptr->gamma_16_from_1);
+   png_ptr->gamma_16_from_1 = NULL;
+   }
+   if (png_ptr->gamma_16_to_1 != NULL)
+   {
+      int i;
+      int istop = (1 << (8 - png_ptr->gamma_shift));
+      for (i = 0; i < istop; i++)
+      {
+         png_free(png_ptr, png_ptr->gamma_16_to_1[i]);
+      }
+   png_free(png_ptr, png_ptr->gamma_16_to_1);
+   png_ptr->gamma_16_to_1 = NULL;
+   }
+#endif /* READ_BACKGROUND || READ_ALPHA_MODE || RGB_TO_GRAY */
+}
+
 /* We build the 8- or 16-bit gamma tables here.  Note that for 16-bit
  * tables, we don't make a full table if we are reducing to 8-bit in
  * the future.  Note also how the gamma_16 tables are segmented so that
@@ -2673,6 +2727,18 @@ png_build_gamma_table(png_structp png_ptr, int bit_depth)
 {
   png_debug(1, "in png_build_gamma_table");
 
+  /* Remove any existing table; this copes with multiple calls to
+   * png_read_update_info.  The warning is because building the gamma tables
+   * multiple times is a performance hit - it's harmless but the ability to call
+   * png_read_update_info() multiple times is new in 1.5.6 so it seems sensible
+   * to warn if the app introduces such a hit.
+   */
+  if (png_ptr->gamma_table != NULL || png_ptr->gamma_16_table != NULL)
+  {
+    png_warning(png_ptr, "gamma table being rebuilt");
+    png_destroy_gamma_table(png_ptr);
+  }
+
   if (bit_depth <= 8)
   {
      png_build_8bit_table(png_ptr, &png_ptr->gamma_table,
diff --git a/pngpriv.h b/pngpriv.h
index 0f06d11cd..ca36fe18a 100644
--- a/pngpriv.h
+++ b/pngpriv.h
@@ -1568,6 +1568,7 @@ PNG_EXTERN png_uint_16 png_gamma_16bit_correct PNGARG((unsigned int value,
     png_fixed_point gamma_value));
 PNG_EXTERN png_byte png_gamma_8bit_correct PNGARG((unsigned int value,
     png_fixed_point gamma_value));
+PNG_EXTERN void png_destroy_gamma_table(png_structp png_ptr);
 PNG_EXTERN void png_build_gamma_table PNGARG((png_structp png_ptr,
     int bit_depth));
 #endif
diff --git a/pngread.c b/pngread.c
index 53b017263..89cf14567 100644
--- a/pngread.c
+++ b/pngread.c
@@ -1032,6 +1032,10 @@ png_read_destroy(png_structp png_ptr, png_infop info_ptr,
    if (end_info_ptr != NULL)
       png_info_destroy(png_ptr, end_info_ptr);
 
+#ifdef PNG_READ_GAMMA_SUPPORTED
+   png_destroy_gamma_table(png_ptr);
+#endif
+
    png_free(png_ptr, png_ptr->zbuf);
    png_free(png_ptr, png_ptr->big_row_buf);
    png_free(png_ptr, png_ptr->prev_row);
@@ -1042,15 +1046,6 @@ png_read_destroy(png_structp png_ptr, png_infop info_ptr,
    png_free(png_ptr, png_ptr->quantize_index);
 #endif
 
-#ifdef PNG_READ_GAMMA_SUPPORTED
-   png_free(png_ptr, png_ptr->gamma_table);
-#endif
-
-#ifdef PNG_READ_BACKGROUND_SUPPORTED
-   png_free(png_ptr, png_ptr->gamma_from_1);
-   png_free(png_ptr, png_ptr->gamma_to_1);
-#endif
-
    if (png_ptr->free_me & PNG_FREE_PLTE)
       png_zfree(png_ptr, png_ptr->palette);
    png_ptr->free_me &= ~PNG_FREE_PLTE;
@@ -1068,42 +1063,6 @@ png_read_destroy(png_structp png_ptr, png_infop info_ptr,
    png_ptr->free_me &= ~PNG_FREE_HIST;
 #endif
 
-#ifdef PNG_READ_GAMMA_SUPPORTED
-   if (png_ptr->gamma_16_table != NULL)
-   {
-      int i;
-      int istop = (1 << (8 - png_ptr->gamma_shift));
-      for (i = 0; i < istop; i++)
-      {
-         png_free(png_ptr, png_ptr->gamma_16_table[i]);
-      }
-   png_free(png_ptr, png_ptr->gamma_16_table);
-   }
-
-#ifdef PNG_READ_BACKGROUND_SUPPORTED
-   if (png_ptr->gamma_16_from_1 != NULL)
-   {
-      int i;
-      int istop = (1 << (8 - png_ptr->gamma_shift));
-      for (i = 0; i < istop; i++)
-      {
-         png_free(png_ptr, png_ptr->gamma_16_from_1[i]);
-      }
-   png_free(png_ptr, png_ptr->gamma_16_from_1);
-   }
-   if (png_ptr->gamma_16_to_1 != NULL)
-   {
-      int i;
-      int istop = (1 << (8 - png_ptr->gamma_shift));
-      for (i = 0; i < istop; i++)
-      {
-         png_free(png_ptr, png_ptr->gamma_16_to_1[i]);
-      }
-   png_free(png_ptr, png_ptr->gamma_16_to_1);
-   }
-#endif
-#endif
-
    inflateEnd(&png_ptr->zstream);
 
 #ifdef PNG_PROGRESSIVE_READ_SUPPORTED
diff --git a/pngrtran.c b/pngrtran.c
index 737970011..e87776ad9 100644
--- a/pngrtran.c
+++ b/pngrtran.c
@@ -1641,8 +1641,9 @@ png_init_read_transformations(png_structp png_ptr)
          /* if (png_ptr->background_gamma_type!=PNG_BACKGROUND_GAMMA_UNKNOWN) */
          else /* color_type != PNG_COLOR_TYPE_PALETTE */
          {
-            png_fixed_point g = PNG_FP_1;
-            png_fixed_point gs = PNG_FP_1;
+            int gs_sig, g_sig;
+            png_fixed_point g = PNG_FP_1;  /* Correction to linear */
+            png_fixed_point gs = PNG_FP_1; /* Correction to screen */
 
             switch (png_ptr->background_gamma_type)
             {
@@ -1666,34 +1667,45 @@ png_init_read_transformations(png_structp png_ptr)
                   png_error(png_ptr, "invalid background gamma type");
             }
 
-            png_ptr->background_1.gray = png_gamma_correct(png_ptr,
-                png_ptr->background.gray, g);
+            g_sig = png_gamma_significant(g);
+            gs_sig = png_gamma_significant(gs);
 
-            png_ptr->background.gray = png_gamma_correct(png_ptr,
-                png_ptr->background.gray, gs);
+            if (g_sig)
+               png_ptr->background_1.gray = png_gamma_correct(png_ptr,
+                   png_ptr->background.gray, g);
+
+            if (gs_sig)
+               png_ptr->background.gray = png_gamma_correct(png_ptr,
+                   png_ptr->background.gray, gs);
 
             if ((png_ptr->background.red != png_ptr->background.green) ||
                 (png_ptr->background.red != png_ptr->background.blue) ||
                 (png_ptr->background.red != png_ptr->background.gray))
             {
                /* RGB or RGBA with color background */
-               png_ptr->background_1.red = png_gamma_correct(png_ptr,
-                   png_ptr->background.red, g);
+               if (g_sig)
+               {
+                  png_ptr->background_1.red = png_gamma_correct(png_ptr,
+                      png_ptr->background.red, g);
 
-               png_ptr->background_1.green = png_gamma_correct(png_ptr,
-                   png_ptr->background.green, g);
+                  png_ptr->background_1.green = png_gamma_correct(png_ptr,
+                      png_ptr->background.green, g);
 
-               png_ptr->background_1.blue = png_gamma_correct(png_ptr,
-                   png_ptr->background.blue, g);
+                  png_ptr->background_1.blue = png_gamma_correct(png_ptr,
+                      png_ptr->background.blue, g);
+               }
 
-               png_ptr->background.red = png_gamma_correct(png_ptr,
-                   png_ptr->background.red, gs);
+               if (gs_sig)
+               {
+                  png_ptr->background.red = png_gamma_correct(png_ptr,
+                      png_ptr->background.red, gs);
 
-               png_ptr->background.green = png_gamma_correct(png_ptr,
-                   png_ptr->background.green, gs);
+                  png_ptr->background.green = png_gamma_correct(png_ptr,
+                      png_ptr->background.green, gs);
 
-               png_ptr->background.blue = png_gamma_correct(png_ptr,
-                   png_ptr->background.blue, gs);
+                  png_ptr->background.blue = png_gamma_correct(png_ptr,
+                      png_ptr->background.blue, gs);
+               }
             }
 
             else
@@ -1705,6 +1717,9 @@ png_init_read_transformations(png_structp png_ptr)
                png_ptr->background.red = png_ptr->background.green
                    = png_ptr->background.blue = png_ptr->background.gray;
             }
+
+            /* The background is now in screen gamma: */
+            png_ptr->background_gamma_type = PNG_BACKGROUND_GAMMA_SCREEN;
          } /* color_type != PNG_COLOR_TYPE_PALETTE */
       }/* png_ptr->transformations & PNG_BACKGROUND */
 
@@ -3404,7 +3419,8 @@ png_build_grayscale_palette(int bit_depth, png_colorp palette)
 
 
 #ifdef PNG_READ_TRANSFORMS_SUPPORTED
-#ifdef PNG_READ_BACKGROUND_SUPPORTED
+#if (defined PNG_READ_BACKGROUND_SUPPORTED) ||\
+   (defined PNG_READ_ALPHA_MODE_SUPPORTED)
 /* Replace any alpha or transparency with the supplied background color.
  * "background" is already in the screen gamma, while "background_1" is
  * at a gamma of 1.0.  Paletted files have already been taken care of.
@@ -4112,7 +4128,7 @@ png_do_compose(png_row_infop row_info, png_bytep row, png_structp png_ptr)
       }
    }
 }
-#endif
+#endif /* PNG_READ_BACKGROUND_SUPPORTED || PNG_READ_ALPHA_MODE_SUPPORTED */
 
 #ifdef PNG_READ_GAMMA_SUPPORTED
 /* Gamma correct the image, avoiding the alpha channel.  Make sure
diff --git a/pngstruct.h b/pngstruct.h
index ec62a78cb..658a25b66 100644
--- a/pngstruct.h
+++ b/pngstruct.h
@@ -157,19 +157,21 @@ struct png_struct_def
    png_uint_32 flush_rows;    /* number of rows written since last flush */
 #endif
 
-#if defined(PNG_READ_GAMMA_SUPPORTED) || defined(PNG_READ_BACKGROUND_SUPPORTED)
+#ifdef PNG_READ_GAMMA_SUPPORTED
    int gamma_shift;      /* number of "insignificant" bits in 16-bit gamma */
    png_fixed_point gamma;        /* file gamma value */
    png_fixed_point screen_gamma; /* screen gamma value (display_exponent) */
-#endif
 
-#if defined(PNG_READ_GAMMA_SUPPORTED) || defined(PNG_READ_BACKGROUND_SUPPORTED)
    png_bytep gamma_table;     /* gamma table for 8-bit depth files */
+   png_uint_16pp gamma_16_table; /* gamma table for 16-bit depth files */
+#if defined(PNG_READ_BACKGROUND_SUPPORTED) || \
+   defined(PNG_READ_ALPHA_MODE_SUPPORTED) || \
+   defined(PNG_READ_RGB_TO_GRAY_SUPPORTED)
    png_bytep gamma_from_1;    /* converts from 1.0 to screen */
    png_bytep gamma_to_1;      /* converts from file to 1.0 */
-   png_uint_16pp gamma_16_table; /* gamma table for 16-bit depth files */
    png_uint_16pp gamma_16_from_1; /* converts from 1.0 to screen */
    png_uint_16pp gamma_16_to_1; /* converts from file to 1.0 */
+#endif /* READ_BACKGROUND || READ_ALPHA_MODE || RGB_TO_GRAY */
 #endif
 
 #if defined(PNG_READ_GAMMA_SUPPORTED) || defined(PNG_sBIT_SUPPORTED)
diff --git a/pngvalid.c b/pngvalid.c
index cad41253c..c8952207d 100644
--- a/pngvalid.c
+++ b/pngvalid.c
@@ -7748,7 +7748,7 @@ gamma_component_validate(PNG_CONST char *name, PNG_CONST validate_info *vi,
                case ALPHA_MODE_OFFSET + PNG_ALPHA_BROKEN:
                case ALPHA_MODE_OFFSET + PNG_ALPHA_OPTIMIZED:
 #           endif /* ALPHA_MODE_SUPPORTED */
-               do_compose = (alpha >= 0 && alpha < 1);
+               do_compose = (alpha > 0 && alpha < 1);
                use_input = (alpha != 0);
                break;
 
diff --git a/test-pngvalid-full.sh b/test-pngvalid-full.sh
index d8c6faa23..cf0e41a78 100755
--- a/test-pngvalid-full.sh
+++ b/test-pngvalid-full.sh
@@ -9,11 +9,11 @@ echo "============ pngvalid-full.sh ==============" >> pngtest-log.txt
 echo "Running test-pngvalid-full.sh"
 for gamma in threshold transform sbit 16-to-8 background alpha-mode "transform --expand16" "background --expand16" "alpha-mode --expand16"
 do
-   if ./pngvalid --gamma-$gamma >> pngtest-log.txt 2>&1
+   if ./pngvalid "$@" --gamma-$gamma >> pngtest-log.txt 2>&1
    then
-      echo "  PASS:" pngvalid "--gamma-$gamma"
+      echo "  PASS: pngvalid" "$@" "--gamma-$gamma"
    else
-      echo "  FAIL:" pngvalid "--gamma-$gamma"
+      echo "  FAIL: pngvalid" "$@" "--gamma-$gamma"
       err=1
    fi
 done
diff --git a/test-pngvalid-simple.sh b/test-pngvalid-simple.sh
index 9eb0c0a06..7d4d9d83c 100755
--- a/test-pngvalid-simple.sh
+++ b/test-pngvalid-simple.sh
@@ -18,11 +18,11 @@ for opts in "--standard" "--standard --progressive-read" \
    "--size" "--size --progressive-read" \
    "--transform"
 do
-   if ./pngvalid  $opts >> pngtest-log.txt 2>&1
+   if ./pngvalid "$@" $opts >> pngtest-log.txt 2>&1
    then
-      echo "  PASS:" pngvalid $opts
+      echo "  PASS: pngvalid" "$@" $opts
    else
-      echo "  FAIL:" pngvalid $opts
+      echo "  FAIL: pngvalid" "$@" $opts
       err=1
    fi
 done