diff --git a/png.c b/png.c
index 53733509c..c2e15f7c5 100644
--- a/png.c
+++ b/png.c
@@ -762,13 +762,13 @@ png_get_copyright(png_const_structrp png_ptr)
 #else
 #  ifdef __STDC__
    return PNG_STRING_NEWLINE \
-     "libpng version 1.6.0beta04 - December 24, 2011" PNG_STRING_NEWLINE \
+     "libpng version 1.6.0beta04 - December 28, 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 1.6.0beta04 - December 24, 2011\
+      return "libpng version 1.6.0beta04 - December 28, 2011\
       Copyright (c) 1998-2011 Glenn Randers-Pehrson\
       Copyright (c) 1996-1997 Andreas Dilger\
       Copyright (c) 1995-1996 Guy Eric Schalnat, Group 42, Inc.";
@@ -884,7 +884,7 @@ png_access_version_number(void)
 #  ifdef PNG_CHECK_cHRM_SUPPORTED
 
 int /* PRIVATE */
-png_check_cHRM_fixed(png_structrp png_ptr,
+png_check_cHRM_fixed(png_const_structrp png_ptr,
    png_fixed_point white_x, png_fixed_point white_y, png_fixed_point red_x,
    png_fixed_point red_y, png_fixed_point green_x, png_fixed_point green_y,
    png_fixed_point blue_x, png_fixed_point blue_y)
@@ -1608,7 +1608,7 @@ png_pow10(int power)
  * precision.
  */
 void /* PRIVATE */
-png_ascii_from_fp(png_structrp png_ptr, png_charp ascii, png_size_t size,
+png_ascii_from_fp(png_const_structrp png_ptr, png_charp ascii, png_size_t size,
     double fp, unsigned int precision)
 {
    /* We use standard functions from math.h, but not printf because
@@ -1922,8 +1922,8 @@ png_ascii_from_fp(png_structrp png_ptr, png_charp ascii, png_size_t size,
 /* Function to format a fixed point value in ASCII.
  */
 void /* PRIVATE */
-png_ascii_from_fixed(png_structrp png_ptr, png_charp ascii, png_size_t size,
-    png_fixed_point fp)
+png_ascii_from_fixed(png_const_structrp png_ptr, png_charp ascii,
+    png_size_t size, png_fixed_point fp)
 {
    /* Require space for 10 decimal digits, a decimal point, a minus sign and a
     * trailing \0, 13 characters:
diff --git a/png.h b/png.h
index ad96b3f1c..1b977678c 100644
--- a/png.h
+++ b/png.h
@@ -1,7 +1,7 @@
 
 /* png.h - header file for PNG reference library
  *
- * libpng version 1.6.0beta04 - December 24, 2011
+ * libpng version 1.6.0beta04 - December 28, 2011
  * Copyright (c) 1998-2011 Glenn Randers-Pehrson
  * (Version 0.96 Copyright (c) 1996, 1997 Andreas Dilger)
  * (Version 0.88 Copyright (c) 1995, 1996 Guy Eric Schalnat, Group 42, Inc.)
@@ -11,7 +11,7 @@
  * Authors and maintainers:
  *   libpng versions 0.71, May 1995, through 0.88, January 1996: Guy Schalnat
  *   libpng versions 0.89c, June 1996, through 0.96, May 1997: Andreas Dilger
- *   libpng versions 0.97, January 1998, through 1.6.0beta04 - December 24, 2011: Glenn
+ *   libpng versions 0.97, January 1998, through 1.6.0beta04 - December 28, 2011: Glenn
  *   See also "Contributing Authors", below.
  *
  * Note about libpng version numbers:
@@ -198,7 +198,7 @@
  *
  * This code is released under the libpng license.
  *
- * libpng versions 1.2.6, August 15, 2004, through 1.6.0beta04, December 24, 2011, are
+ * libpng versions 1.2.6, August 15, 2004, through 1.6.0beta04, December 28, 2011, are
  * Copyright (c) 2004, 2006-2011 Glenn Randers-Pehrson, and are
  * distributed according to the same disclaimer and license as libpng-1.2.5
  * with the following individual added to the list of Contributing Authors:
@@ -310,7 +310,7 @@
  * Y2K compliance in libpng:
  * =========================
  *
- *    December 24, 2011
+ *    December 28, 2011
  *
  *    Since the PNG Development group is an ad-hoc body, we can't make
  *    an official declaration.
@@ -376,7 +376,7 @@
 /* Version information for png.h - this should match the version in png.c */
 #define PNG_LIBPNG_VER_STRING "1.6.0beta04"
 #define PNG_HEADER_VERSION_STRING \
-     " libpng version 1.6.0beta04 - December 24, 2011\n"
+     " libpng version 1.6.0beta04 - December 28, 2011\n"
 
 #define PNG_LIBPNG_VER_SONUM   16
 #define PNG_LIBPNG_VER_DLLNUM  16
@@ -2000,8 +2000,8 @@ PNG_EXPORT(112, png_bytepp, png_get_rows, (png_const_structrp png_ptr,
 /* Set row_pointers, which is an array of pointers to scanlines for use
  * by png_write_png().
  */
-PNG_EXPORT(113, void, png_set_rows, (png_structrp png_ptr, png_inforp info_ptr,
-    png_bytepp row_pointers));
+PNG_EXPORT(113, void, png_set_rows, (png_const_structrp png_ptr,
+    png_inforp info_ptr, png_bytepp row_pointers));
 #endif
 
 /* Returns number of color channels in image. */
@@ -2065,7 +2065,7 @@ PNG_EXPORT(129, png_int_32, png_get_y_offset_microns,
 
 /* Returns pointer to signature string read from PNG header */
 PNG_EXPORT(130, png_const_bytep, png_get_signature, (png_const_structrp png_ptr,
-    png_inforp info_ptr));
+    png_const_inforp info_ptr));
 
 #ifdef PNG_bKGD_SUPPORTED
 PNG_EXPORT(131, png_uint_32, png_get_bKGD, (png_const_structrp png_ptr,
@@ -2073,8 +2073,8 @@ PNG_EXPORT(131, png_uint_32, png_get_bKGD, (png_const_structrp png_ptr,
 #endif
 
 #ifdef PNG_bKGD_SUPPORTED
-PNG_EXPORT(132, void, png_set_bKGD, (png_structrp png_ptr, png_inforp info_ptr,
-    png_const_color_16p background));
+PNG_EXPORT(132, void, png_set_bKGD, (png_const_structrp png_ptr,
+    png_inforp info_ptr, png_const_color_16p background));
 #endif
 
 #ifdef PNG_cHRM_SUPPORTED
@@ -2104,20 +2104,21 @@ PNG_FIXED_EXPORT(231, png_uint_32, png_get_cHRM_XYZ_fixed,
 #endif
 
 #ifdef PNG_cHRM_SUPPORTED
-PNG_FP_EXPORT(135, void, png_set_cHRM, (png_structrp png_ptr, png_inforp info_ptr,
+PNG_FP_EXPORT(135, void, png_set_cHRM, (png_const_structrp png_ptr,
+    png_inforp info_ptr,
     double white_x, double white_y, double red_x, double red_y, double green_x,
     double green_y, double blue_x, double blue_y));
-PNG_FP_EXPORT(232, void, png_set_cHRM_XYZ, (png_structrp png_ptr,
+PNG_FP_EXPORT(232, void, png_set_cHRM_XYZ, (png_const_structrp png_ptr,
     png_inforp info_ptr, double red_X, double red_Y, double red_Z,
     double green_X, double green_Y, double green_Z, double blue_X,
     double blue_Y, double blue_Z));
-PNG_FIXED_EXPORT(136, void, png_set_cHRM_fixed, (png_structrp png_ptr,
+PNG_FIXED_EXPORT(136, void, png_set_cHRM_fixed, (png_const_structrp png_ptr,
     png_inforp info_ptr, png_fixed_point int_white_x,
     png_fixed_point int_white_y, png_fixed_point int_red_x,
     png_fixed_point int_red_y, png_fixed_point int_green_x,
     png_fixed_point int_green_y, png_fixed_point int_blue_x,
     png_fixed_point int_blue_y));
-PNG_FIXED_EXPORT(233, void, png_set_cHRM_XYZ_fixed, (png_structrp png_ptr,
+PNG_FIXED_EXPORT(233, void, png_set_cHRM_XYZ_fixed, (png_const_structrp png_ptr,
     png_inforp info_ptr, png_fixed_point int_red_X, png_fixed_point int_red_Y,
     png_fixed_point int_red_Z, png_fixed_point int_green_X,
     png_fixed_point int_green_Y, png_fixed_point int_green_Z,
@@ -2134,9 +2135,9 @@ PNG_FIXED_EXPORT(138, png_uint_32, png_get_gAMA_fixed,
 #endif
 
 #ifdef PNG_gAMA_SUPPORTED
-PNG_FP_EXPORT(139, void, png_set_gAMA, (png_structrp png_ptr,
+PNG_FP_EXPORT(139, void, png_set_gAMA, (png_const_structrp png_ptr,
     png_inforp info_ptr, double file_gamma));
-PNG_FIXED_EXPORT(140, void, png_set_gAMA_fixed, (png_structrp png_ptr,
+PNG_FIXED_EXPORT(140, void, png_set_gAMA_fixed, (png_const_structrp png_ptr,
     png_inforp info_ptr, png_fixed_point int_file_gamma));
 #endif
 
@@ -2146,18 +2147,19 @@ PNG_EXPORT(141, png_uint_32, png_get_hIST, (png_const_structrp png_ptr,
 #endif
 
 #ifdef PNG_hIST_SUPPORTED
-PNG_EXPORT(142, void, png_set_hIST, (png_structrp png_ptr, png_inforp info_ptr,
-    png_const_uint_16p hist));
+PNG_EXPORT(142, void, png_set_hIST, (png_const_structrp png_ptr,
+    png_inforp info_ptr, png_const_uint_16p hist));
 #endif
 
 PNG_EXPORT(143, png_uint_32, png_get_IHDR, (png_const_structrp png_ptr,
-    png_inforp info_ptr, png_uint_32 *width, png_uint_32 *height,
+    png_const_inforp info_ptr, png_uint_32 *width, png_uint_32 *height,
     int *bit_depth, int *color_type, int *interlace_method,
     int *compression_method, int *filter_method));
 
-PNG_EXPORT(144, void, png_set_IHDR, (png_structrp png_ptr, png_inforp info_ptr,
-    png_uint_32 width, png_uint_32 height, int bit_depth, int color_type,
-    int interlace_method, int compression_method, int filter_method));
+PNG_EXPORT(144, void, png_set_IHDR, (png_const_structrp png_ptr,
+    png_inforp info_ptr, png_uint_32 width, png_uint_32 height, int bit_depth,
+    int color_type, int interlace_method, int compression_method,
+    int filter_method));
 
 #ifdef PNG_oFFs_SUPPORTED
 PNG_EXPORT(145, png_uint_32, png_get_oFFs, (png_const_structrp png_ptr,
@@ -2166,8 +2168,9 @@ PNG_EXPORT(145, png_uint_32, png_get_oFFs, (png_const_structrp png_ptr,
 #endif
 
 #ifdef PNG_oFFs_SUPPORTED
-PNG_EXPORT(146, void, png_set_oFFs, (png_structrp png_ptr, png_inforp info_ptr,
-    png_int_32 offset_x, png_int_32 offset_y, int unit_type));
+PNG_EXPORT(146, void, png_set_oFFs, (png_const_structrp png_ptr,
+    png_inforp info_ptr, png_int_32 offset_x, png_int_32 offset_y,
+    int unit_type));
 #endif
 
 #ifdef PNG_pCAL_SUPPORTED
@@ -2178,9 +2181,9 @@ PNG_EXPORT(147, png_uint_32, png_get_pCAL, (png_const_structrp png_ptr,
 #endif
 
 #ifdef PNG_pCAL_SUPPORTED
-PNG_EXPORT(148, void, png_set_pCAL, (png_structrp png_ptr, png_inforp info_ptr,
-    png_const_charp purpose, png_int_32 X0, png_int_32 X1, int type,
-    int nparams, png_const_charp units, png_charpp params));
+PNG_EXPORT(148, void, png_set_pCAL, (png_const_structrp png_ptr,
+    png_inforp info_ptr, png_const_charp purpose, png_int_32 X0, png_int_32 X1,
+    int type, int nparams, png_const_charp units, png_charpp params));
 #endif
 
 #ifdef PNG_pHYs_SUPPORTED
@@ -2190,15 +2193,15 @@ PNG_EXPORT(149, png_uint_32, png_get_pHYs, (png_const_structrp png_ptr,
 #endif
 
 #ifdef PNG_pHYs_SUPPORTED
-PNG_EXPORT(150, void, png_set_pHYs, (png_structrp png_ptr, png_inforp info_ptr,
-    png_uint_32 res_x, png_uint_32 res_y, int unit_type));
+PNG_EXPORT(150, void, png_set_pHYs, (png_const_structrp png_ptr,
+    png_inforp info_ptr, png_uint_32 res_x, png_uint_32 res_y, int unit_type));
 #endif
 
 PNG_EXPORT(151, png_uint_32, png_get_PLTE, (png_const_structrp png_ptr,
    png_const_inforp info_ptr, png_colorp *palette, int *num_palette));
 
-PNG_EXPORT(152, void, png_set_PLTE, (png_structrp png_ptr, png_inforp info_ptr,
-    png_const_colorp palette, int num_palette));
+PNG_EXPORT(152, void, png_set_PLTE, (png_structrp png_ptr,
+    png_inforp info_ptr, png_const_colorp palette, int num_palette));
 
 #ifdef PNG_sBIT_SUPPORTED
 PNG_EXPORT(153, png_uint_32, png_get_sBIT, (png_const_structrp png_ptr,
@@ -2206,8 +2209,8 @@ PNG_EXPORT(153, png_uint_32, png_get_sBIT, (png_const_structrp png_ptr,
 #endif
 
 #ifdef PNG_sBIT_SUPPORTED
-PNG_EXPORT(154, void, png_set_sBIT, (png_structrp png_ptr, png_inforp info_ptr,
-    png_const_color_8p sig_bit));
+PNG_EXPORT(154, void, png_set_sBIT, (png_const_structrp png_ptr,
+    png_inforp info_ptr, png_const_color_8p sig_bit));
 #endif
 
 #ifdef PNG_sRGB_SUPPORTED
@@ -2216,9 +2219,9 @@ PNG_EXPORT(155, png_uint_32, png_get_sRGB, (png_const_structrp png_ptr,
 #endif
 
 #ifdef PNG_sRGB_SUPPORTED
-PNG_EXPORT(156, void, png_set_sRGB, (png_structrp png_ptr, png_inforp info_ptr,
-    int srgb_intent));
-PNG_EXPORT(157, void, png_set_sRGB_gAMA_and_cHRM, (png_structrp png_ptr,
+PNG_EXPORT(156, void, png_set_sRGB, (png_const_structrp png_ptr,
+    png_inforp info_ptr, int srgb_intent));
+PNG_EXPORT(157, void, png_set_sRGB_gAMA_and_cHRM, (png_const_structrp png_ptr,
     png_inforp info_ptr, int srgb_intent));
 #endif
 
@@ -2229,9 +2232,9 @@ PNG_EXPORT(158, png_uint_32, png_get_iCCP, (png_const_structrp png_ptr,
 #endif
 
 #ifdef PNG_iCCP_SUPPORTED
-PNG_EXPORT(159, void, png_set_iCCP, (png_structrp png_ptr, png_inforp info_ptr,
-    png_const_charp name, int compression_type, png_const_bytep profile,
-    png_uint_32 proflen));
+PNG_EXPORT(159, void, png_set_iCCP, (png_const_structrp png_ptr,
+    png_inforp info_ptr, png_const_charp name, int compression_type,
+    png_const_bytep profile, png_uint_32 proflen));
 #endif
 
 #ifdef PNG_sPLT_SUPPORTED
@@ -2240,8 +2243,8 @@ PNG_EXPORT(160, png_uint_32, png_get_sPLT, (png_const_structrp png_ptr,
 #endif
 
 #ifdef PNG_sPLT_SUPPORTED
-PNG_EXPORT(161, void, png_set_sPLT, (png_structrp png_ptr, png_inforp info_ptr,
-    png_const_sPLT_tp entries, int nentries));
+PNG_EXPORT(161, void, png_set_sPLT, (png_const_structrp png_ptr,
+    png_inforp info_ptr, png_const_sPLT_tp entries, int nentries));
 #endif
 
 #ifdef PNG_TEXT_SUPPORTED
@@ -2258,8 +2261,8 @@ PNG_EXPORT(162, png_uint_32, png_get_text, (png_const_structrp png_ptr,
  */
 
 #ifdef PNG_TEXT_SUPPORTED
-PNG_EXPORT(163, void, png_set_text, (png_structrp png_ptr, png_inforp info_ptr,
-    png_const_textp text_ptr, int num_text));
+PNG_EXPORT(163, void, png_set_text, (png_const_structrp png_ptr,
+    png_inforp info_ptr, png_const_textp text_ptr, int num_text));
 #endif
 
 #ifdef PNG_tIME_SUPPORTED
@@ -2268,8 +2271,8 @@ PNG_EXPORT(164, png_uint_32, png_get_tIME, (png_const_structrp png_ptr,
 #endif
 
 #ifdef PNG_tIME_SUPPORTED
-PNG_EXPORT(165, void, png_set_tIME, (png_structrp png_ptr, png_inforp info_ptr,
-    png_const_timep mod_time));
+PNG_EXPORT(165, void, png_set_tIME, (png_const_structrp png_ptr,
+    png_inforp info_ptr, png_const_timep mod_time));
 #endif
 
 #ifdef PNG_tRNS_SUPPORTED
@@ -2279,8 +2282,8 @@ PNG_EXPORT(166, png_uint_32, png_get_tRNS, (png_const_structrp png_ptr,
 #endif
 
 #ifdef PNG_tRNS_SUPPORTED
-PNG_EXPORT(167, void, png_set_tRNS, (png_structrp png_ptr, png_inforp info_ptr,
-    png_const_bytep trans_alpha, int num_trans,
+PNG_EXPORT(167, void, png_set_tRNS, (png_structrp png_ptr,
+    png_inforp info_ptr, png_const_bytep trans_alpha, int num_trans,
     png_const_color_16p trans_color));
 #endif
 
@@ -2302,13 +2305,14 @@ PNG_EXPORT(169, png_uint_32, png_get_sCAL_s,
     (png_const_structrp png_ptr, png_const_inforp info_ptr, int *unit,
     png_charpp swidth, png_charpp sheight));
 
-PNG_FP_EXPORT(170, void, png_set_sCAL, (png_structrp png_ptr, png_inforp info_ptr,
-    int unit, double width, double height));
-PNG_FIXED_EXPORT(213, void, png_set_sCAL_fixed, (png_structrp png_ptr,
+PNG_FP_EXPORT(170, void, png_set_sCAL, (png_const_structrp png_ptr,
+    png_inforp info_ptr, int unit, double width, double height));
+PNG_FIXED_EXPORT(213, void, png_set_sCAL_fixed, (png_const_structrp png_ptr,
    png_inforp info_ptr, int unit, png_fixed_point width,
    png_fixed_point height));
-PNG_EXPORT(171, void, png_set_sCAL_s, (png_structrp png_ptr, png_inforp info_ptr,
-    int unit, png_const_charp swidth, png_const_charp sheight));
+PNG_EXPORT(171, void, png_set_sCAL_s, (png_const_structrp png_ptr,
+    png_inforp info_ptr, int unit,
+    png_const_charp swidth, png_const_charp sheight));
 #endif /* PNG_sCAL_SUPPORTED */
 
 #ifdef PNG_HANDLE_AS_UNKNOWN_SUPPORTED
@@ -2333,11 +2337,11 @@ PNG_EXPORT(173, int, png_handle_as_unknown, (png_structrp png_ptr,
     png_const_bytep chunk_name));
 #endif
 #ifdef PNG_UNKNOWN_CHUNKS_SUPPORTED
-PNG_EXPORT(174, void, png_set_unknown_chunks, (png_structrp png_ptr,
+PNG_EXPORT(174, void, png_set_unknown_chunks, (png_const_structrp png_ptr,
     png_inforp info_ptr, png_const_unknown_chunkp unknowns,
     int num_unknowns));
-PNG_EXPORT(175, void, png_set_unknown_chunk_location, (png_structrp png_ptr,
-    png_inforp info_ptr, int chunk, int location));
+PNG_EXPORT(175, void, png_set_unknown_chunk_location,
+    (png_const_structrp png_ptr, png_inforp info_ptr, int chunk, int location));
 PNG_EXPORT(176, int, png_get_unknown_chunks, (png_const_structrp png_ptr,
     png_const_inforp info_ptr, png_unknown_chunkpp entries));
 #endif
@@ -2348,7 +2352,7 @@ PNG_EXPORT(176, int, png_get_unknown_chunks, (png_const_structrp png_ptr,
  */
 PNG_EXPORT(177, void, png_set_invalid, (png_const_structrp png_ptr,
     png_inforp info_ptr, int mask));
-
+ 
 #ifdef PNG_INFO_IMAGE_SUPPORTED
 /* The "params" pointer is currently not used and is for future expansion. */
 PNG_EXPORT(178, void, png_read_png, (png_structrp png_ptr, png_inforp info_ptr,
diff --git a/pngget.c b/pngget.c
index 288364333..4e1df5f30 100644
--- a/pngget.c
+++ b/pngget.c
@@ -432,7 +432,7 @@ png_get_channels(png_const_structrp png_ptr, png_const_inforp info_ptr)
 }
 
 png_const_bytep PNGAPI
-png_get_signature(png_const_structrp png_ptr, png_inforp info_ptr)
+png_get_signature(png_const_structrp png_ptr, png_const_inforp info_ptr)
 {
    if (png_ptr != NULL && info_ptr != NULL)
       return(info_ptr->signature);
@@ -733,7 +733,7 @@ png_get_hIST(png_const_structrp png_ptr, png_const_inforp info_ptr,
 #endif
 
 png_uint_32 PNGAPI
-png_get_IHDR(png_const_structrp png_ptr, png_inforp info_ptr,
+png_get_IHDR(png_const_structrp png_ptr, png_const_inforp info_ptr,
     png_uint_32 *width, png_uint_32 *height, int *bit_depth,
     int *color_type, int *interlace_type, int *compression_type,
     int *filter_type)
@@ -975,7 +975,8 @@ png_get_text(png_const_structrp png_ptr, png_const_inforp info_ptr,
 
 #ifdef PNG_tIME_SUPPORTED
 png_uint_32 PNGAPI
-png_get_tIME(png_const_structrp png_ptr, png_inforp info_ptr, png_timep *mod_time)
+png_get_tIME(png_const_structrp png_ptr, png_inforp info_ptr,
+    png_timep *mod_time)
 {
    png_debug1(1, "in %s retrieval function", "tIME");
 
diff --git a/pngpriv.h b/pngpriv.h
index f5ae898f5..8d7fd0c52 100644
--- a/pngpriv.h
+++ b/pngpriv.h
@@ -874,7 +874,7 @@ PNG_EXTERN void png_write_iTXt PNGARG((png_structrp png_ptr,
 #endif
 
 #ifdef PNG_TEXT_SUPPORTED  /* Added at version 1.0.14 and 1.2.4 */
-PNG_EXTERN int png_set_text_2 PNGARG((png_structrp png_ptr,
+PNG_EXTERN int png_set_text_2 PNGARG((png_const_structrp png_ptr,
     png_inforp info_ptr, png_const_textp text_ptr, int num_text));
 #endif
 
@@ -1316,7 +1316,7 @@ PNG_EXTERN void png_do_write_intrapixel PNGARG((png_row_infop row_info,
 
 /* Added at libpng version 1.4.0 */
 #ifdef PNG_CHECK_cHRM_SUPPORTED
-PNG_EXTERN int png_check_cHRM_fixed PNGARG((png_structrp png_ptr,
+PNG_EXTERN int png_check_cHRM_fixed PNGARG((png_const_structrp png_ptr,
     png_fixed_point int_white_x, png_fixed_point int_white_y,
     png_fixed_point int_red_x, png_fixed_point int_red_y, png_fixed_point
     int_green_x, png_fixed_point int_green_y, png_fixed_point int_blue_x,
@@ -1452,12 +1452,12 @@ PNG_EXTERN void png_formatted_warning(png_const_structrp png_ptr,
 #define PNG_sCAL_MAX_DIGITS (PNG_sCAL_PRECISION+1/*.*/+1/*E*/+10/*exponent*/)
 
 #ifdef PNG_FLOATING_POINT_SUPPORTED
-PNG_EXTERN void png_ascii_from_fp PNGARG((png_structrp png_ptr, png_charp ascii,
-    png_size_t size, double fp, unsigned int precision));
+PNG_EXTERN void png_ascii_from_fp PNGARG((png_const_structrp png_ptr,
+    png_charp ascii, png_size_t size, double fp, unsigned int precision));
 #endif /* FLOATING_POINT */
 
 #ifdef PNG_FIXED_POINT_SUPPORTED
-PNG_EXTERN void png_ascii_from_fixed PNGARG((png_structrp png_ptr,
+PNG_EXTERN void png_ascii_from_fixed PNGARG((png_const_structrp png_ptr,
     png_charp ascii, png_size_t size, png_fixed_point fp));
 #endif /* FIXED_POINT */
 #endif /* READ_sCAL */
diff --git a/pngread.c b/pngread.c
index 3348a1b2a..174298be8 100644
--- a/pngread.c
+++ b/pngread.c
@@ -903,12 +903,6 @@ png_read_destroy(png_structrp png_ptr)
    png_ptr->free_me &= ~PNG_FREE_TRNS;
 #endif
 
-#ifdef PNG_READ_hIST_SUPPORTED
-   if (png_ptr->free_me & PNG_FREE_HIST)
-      png_free(png_ptr, png_ptr->hist);
-   png_ptr->free_me &= ~PNG_FREE_HIST;
-#endif
-
    inflateEnd(&png_ptr->zstream);
 
 #ifdef PNG_PROGRESSIVE_READ_SUPPORTED
@@ -1437,7 +1431,7 @@ png_image_read_composite(png_voidp argument)
    png_imagep image = display->image;
    png_structrp png_ptr = image->opaque->png_ptr;
    png_byte interlace_type = png_ptr->interlaced;
-   int passes = 0;
+   int passes;
 
    switch (interlace_type)
    {
@@ -1450,6 +1444,7 @@ png_image_read_composite(png_voidp argument)
          break;
 
       default:
+         passes = 0;
          png_error(png_ptr, "unknown interlace type");
    }
 
@@ -1567,7 +1562,7 @@ png_image_read_background(png_voidp argument)
    png_byte interlace_type = png_ptr->interlaced;
    png_uint_32 height = image->height;
    png_uint_32 width = image->width;
-   int pass, passes = 0;
+   int pass, passes;
 
    /* Double check the convoluted logic below.  We expect to get here with
     * libpng doing rgb to gray and gamma correction but background processing
@@ -1599,6 +1594,7 @@ png_image_read_background(png_voidp argument)
          break;
 
       default:
+         passes = 0;
          png_error(png_ptr, "unknown interlace type");
    }
 
diff --git a/pngset.c b/pngset.c
index e0c819691..e3849a324 100644
--- a/pngset.c
+++ b/pngset.c
@@ -22,7 +22,7 @@
 
 #ifdef PNG_bKGD_SUPPORTED
 void PNGAPI
-png_set_bKGD(png_structrp png_ptr, png_inforp info_ptr,
+png_set_bKGD(png_const_structrp png_ptr, png_inforp info_ptr,
     png_const_color_16p background)
 {
    png_debug1(1, "in %s storage function", "bKGD");
@@ -37,7 +37,7 @@ png_set_bKGD(png_structrp png_ptr, png_inforp info_ptr,
 
 #ifdef PNG_cHRM_SUPPORTED
 void PNGFAPI
-png_set_cHRM_fixed(png_structrp png_ptr, png_inforp info_ptr,
+png_set_cHRM_fixed(png_const_structrp png_ptr, png_inforp info_ptr,
     png_fixed_point white_x, png_fixed_point white_y, png_fixed_point red_x,
     png_fixed_point red_y, png_fixed_point green_x, png_fixed_point green_y,
     png_fixed_point blue_x, png_fixed_point blue_y)
@@ -65,7 +65,7 @@ png_set_cHRM_fixed(png_structrp png_ptr, png_inforp info_ptr,
 }
 
 void PNGFAPI
-png_set_cHRM_XYZ_fixed(png_structrp png_ptr, png_inforp info_ptr,
+png_set_cHRM_XYZ_fixed(png_const_structrp png_ptr, png_inforp info_ptr,
     png_fixed_point int_red_X, png_fixed_point int_red_Y,
     png_fixed_point int_red_Z, png_fixed_point int_green_X,
     png_fixed_point int_green_Y, png_fixed_point int_green_Z,
@@ -99,7 +99,7 @@ png_set_cHRM_XYZ_fixed(png_structrp png_ptr, png_inforp info_ptr,
 
 #  ifdef PNG_FLOATING_POINT_SUPPORTED
 void PNGAPI
-png_set_cHRM(png_structrp png_ptr, png_inforp info_ptr,
+png_set_cHRM(png_const_structrp png_ptr, png_inforp info_ptr,
     double white_x, double white_y, double red_x, double red_y,
     double green_x, double green_y, double blue_x, double blue_y)
 {
@@ -115,7 +115,7 @@ png_set_cHRM(png_structrp png_ptr, png_inforp info_ptr,
 }
 
 void PNGAPI
-png_set_cHRM_XYZ(png_structrp png_ptr, png_inforp info_ptr, double red_X,
+png_set_cHRM_XYZ(png_const_structrp png_ptr, png_inforp info_ptr, double red_X,
     double red_Y, double red_Z, double green_X, double green_Y, double green_Z,
     double blue_X, double blue_Y, double blue_Z)
 {
@@ -136,8 +136,8 @@ png_set_cHRM_XYZ(png_structrp png_ptr, png_inforp info_ptr, double red_X,
 
 #ifdef PNG_gAMA_SUPPORTED
 void PNGFAPI
-png_set_gAMA_fixed(png_structrp png_ptr, png_inforp info_ptr, png_fixed_point
-    file_gamma)
+png_set_gAMA_fixed(png_const_structrp png_ptr, png_inforp info_ptr,
+    png_fixed_point file_gamma)
 {
    png_debug1(1, "in %s storage function", "gAMA");
 
@@ -164,7 +164,7 @@ png_set_gAMA_fixed(png_structrp png_ptr, png_inforp info_ptr, png_fixed_point
 
 #  ifdef PNG_FLOATING_POINT_SUPPORTED
 void PNGAPI
-png_set_gAMA(png_structrp png_ptr, png_inforp info_ptr, double file_gamma)
+png_set_gAMA(png_const_structrp png_ptr, png_inforp info_ptr, double file_gamma)
 {
    png_set_gAMA_fixed(png_ptr, info_ptr, png_fixed(png_ptr, file_gamma,
        "png_set_gAMA"));
@@ -174,7 +174,8 @@ png_set_gAMA(png_structrp png_ptr, png_inforp info_ptr, double file_gamma)
 
 #ifdef PNG_hIST_SUPPORTED
 void PNGAPI
-png_set_hIST(png_structrp png_ptr, png_inforp info_ptr, png_const_uint_16p hist)
+png_set_hIST(png_const_structrp png_ptr, png_inforp info_ptr,
+    png_const_uint_16p hist)
 {
    int i;
 
@@ -197,26 +198,26 @@ png_set_hIST(png_structrp png_ptr, png_inforp info_ptr, png_const_uint_16p hist)
    /* Changed from info->num_palette to PNG_MAX_PALETTE_LENGTH in
     * version 1.2.1
     */
-   png_ptr->hist = (png_uint_16p)png_malloc_warn(png_ptr,
-       PNG_MAX_PALETTE_LENGTH * png_sizeof(png_uint_16));
+   info_ptr->hist = png_voidcast(png_uint_16p, png_malloc_warn(png_ptr,
+       PNG_MAX_PALETTE_LENGTH * png_sizeof(png_uint_16)));
 
-   if (png_ptr->hist == NULL)
+   if (info_ptr->hist == NULL)
    {
       png_warning(png_ptr, "Insufficient memory for hIST chunk data");
       return;
    }
 
-   for (i = 0; i < info_ptr->num_palette; i++)
-      png_ptr->hist[i] = hist[i];
-
-   info_ptr->hist = png_ptr->hist;
-   info_ptr->valid |= PNG_INFO_hIST;
    info_ptr->free_me |= PNG_FREE_HIST;
+
+   for (i = 0; i < info_ptr->num_palette; i++)
+      info_ptr->hist[i] = hist[i];
+
+   info_ptr->valid |= PNG_INFO_hIST;
 }
 #endif
 
 void PNGAPI
-png_set_IHDR(png_structrp png_ptr, png_inforp info_ptr,
+png_set_IHDR(png_const_structrp png_ptr, png_inforp info_ptr,
     png_uint_32 width, png_uint_32 height, int bit_depth,
     int color_type, int interlace_type, int compression_type,
     int filter_type)
@@ -266,7 +267,7 @@ png_set_IHDR(png_structrp png_ptr, png_inforp info_ptr,
 
 #ifdef PNG_oFFs_SUPPORTED
 void PNGAPI
-png_set_oFFs(png_structrp png_ptr, png_inforp info_ptr,
+png_set_oFFs(png_const_structrp png_ptr, png_inforp info_ptr,
     png_int_32 offset_x, png_int_32 offset_y, int unit_type)
 {
    png_debug1(1, "in %s storage function", "oFFs");
@@ -283,7 +284,7 @@ png_set_oFFs(png_structrp png_ptr, png_inforp info_ptr,
 
 #ifdef PNG_pCAL_SUPPORTED
 void PNGAPI
-png_set_pCAL(png_structrp png_ptr, png_inforp info_ptr,
+png_set_pCAL(png_const_structrp png_ptr, png_inforp info_ptr,
     png_const_charp purpose, png_int_32 X0, png_int_32 X1, int type,
     int nparams, png_const_charp units, png_charpp params)
 {
@@ -375,7 +376,7 @@ png_set_pCAL(png_structrp png_ptr, png_inforp info_ptr,
 
 #ifdef PNG_sCAL_SUPPORTED
 void PNGAPI
-png_set_sCAL_s(png_structrp png_ptr, png_inforp info_ptr,
+png_set_sCAL_s(png_const_structrp png_ptr, png_inforp info_ptr,
     int unit, png_const_charp swidth, png_const_charp sheight)
 {
    png_size_t lengthw = 0, lengthh = 0;
@@ -438,8 +439,8 @@ png_set_sCAL_s(png_structrp png_ptr, png_inforp info_ptr,
 
 #  ifdef PNG_FLOATING_POINT_SUPPORTED
 void PNGAPI
-png_set_sCAL(png_structrp png_ptr, png_inforp info_ptr, int unit, double width,
-    double height)
+png_set_sCAL(png_const_structrp png_ptr, png_inforp info_ptr, int unit,
+    double width, double height)
 {
    png_debug1(1, "in %s storage function", "sCAL");
 
@@ -468,7 +469,7 @@ png_set_sCAL(png_structrp png_ptr, png_inforp info_ptr, int unit, double width,
 
 #  ifdef PNG_FIXED_POINT_SUPPORTED
 void PNGAPI
-png_set_sCAL_fixed(png_structrp png_ptr, png_inforp info_ptr, int unit,
+png_set_sCAL_fixed(png_const_structrp png_ptr, png_inforp info_ptr, int unit,
     png_fixed_point width, png_fixed_point height)
 {
    png_debug1(1, "in %s storage function", "sCAL");
@@ -497,7 +498,7 @@ png_set_sCAL_fixed(png_structrp png_ptr, png_inforp info_ptr, int unit,
 
 #ifdef PNG_pHYs_SUPPORTED
 void PNGAPI
-png_set_pHYs(png_structrp png_ptr, png_inforp info_ptr,
+png_set_pHYs(png_const_structrp png_ptr, png_inforp info_ptr,
     png_uint_32 res_x, png_uint_32 res_y, int unit_type)
 {
    png_debug1(1, "in %s storage function", "pHYs");
@@ -537,6 +538,9 @@ png_set_PLTE(png_structrp png_ptr, png_inforp info_ptr,
    /* It may not actually be necessary to set png_ptr->palette here;
     * we do it for backward compatibility with the way the png_handle_tRNS
     * function used to do the allocation.
+    *
+    * 1.6.0: the above statement appears to be incorrect; something has to set
+    * the palette inside png_struct on read.
     */
    png_free_data(png_ptr, info_ptr, PNG_FREE_PLTE, 0);
 
@@ -558,7 +562,7 @@ png_set_PLTE(png_structrp png_ptr, png_inforp info_ptr,
 
 #ifdef PNG_sBIT_SUPPORTED
 void PNGAPI
-png_set_sBIT(png_structrp png_ptr, png_inforp info_ptr,
+png_set_sBIT(png_const_structrp png_ptr, png_inforp info_ptr,
     png_const_color_8p sig_bit)
 {
    png_debug1(1, "in %s storage function", "sBIT");
@@ -573,7 +577,7 @@ png_set_sBIT(png_structrp png_ptr, png_inforp info_ptr,
 
 #ifdef PNG_sRGB_SUPPORTED
 void PNGAPI
-png_set_sRGB(png_structrp png_ptr, png_inforp info_ptr, int srgb_intent)
+png_set_sRGB(png_const_structrp png_ptr, png_inforp info_ptr, int srgb_intent)
 {
    png_debug1(1, "in %s storage function", "sRGB");
 
@@ -585,7 +589,7 @@ png_set_sRGB(png_structrp png_ptr, png_inforp info_ptr, int srgb_intent)
 }
 
 void PNGAPI
-png_set_sRGB_gAMA_and_cHRM(png_structrp png_ptr, png_inforp info_ptr,
+png_set_sRGB_gAMA_and_cHRM(png_const_structrp png_ptr, png_inforp info_ptr,
     int srgb_intent)
 {
    png_debug1(1, "in %s storage function", "sRGB_gAMA_and_cHRM");
@@ -614,7 +618,7 @@ png_set_sRGB_gAMA_and_cHRM(png_structrp png_ptr, png_inforp info_ptr,
 
 #ifdef PNG_iCCP_SUPPORTED
 void PNGAPI
-png_set_iCCP(png_structrp png_ptr, png_inforp info_ptr,
+png_set_iCCP(png_const_structrp png_ptr, png_inforp info_ptr,
     png_const_charp name, int compression_type,
     png_const_bytep profile, png_uint_32 proflen)
 {
@@ -665,8 +669,8 @@ png_set_iCCP(png_structrp png_ptr, png_inforp info_ptr,
 
 #ifdef PNG_TEXT_SUPPORTED
 void PNGAPI
-png_set_text(png_structrp png_ptr, png_inforp info_ptr, png_const_textp text_ptr,
-    int num_text)
+png_set_text(png_const_structrp png_ptr, png_inforp info_ptr,
+    png_const_textp text_ptr, int num_text)
 {
    int ret;
    ret = png_set_text_2(png_ptr, info_ptr, text_ptr, num_text);
@@ -676,7 +680,7 @@ png_set_text(png_structrp png_ptr, png_inforp info_ptr, png_const_textp text_ptr
 }
 
 int /* PRIVATE */
-png_set_text_2(png_structrp png_ptr, png_inforp info_ptr,
+png_set_text_2(png_const_structrp png_ptr, png_inforp info_ptr,
     png_const_textp text_ptr, int num_text)
 {
    int i;
@@ -856,7 +860,8 @@ png_set_text_2(png_structrp png_ptr, png_inforp info_ptr,
 
 #ifdef PNG_tIME_SUPPORTED
 void PNGAPI
-png_set_tIME(png_structrp png_ptr, png_inforp info_ptr, png_const_timep mod_time)
+png_set_tIME(png_const_structrp png_ptr, png_inforp info_ptr,
+    png_const_timep mod_time)
 {
    png_debug1(1, "in %s storage function", "tIME");
 
@@ -893,13 +898,17 @@ png_set_tRNS(png_structrp png_ptr, png_inforp info_ptr,
        /* It may not actually be necessary to set png_ptr->trans_alpha here;
         * we do it for backward compatibility with the way the png_handle_tRNS
         * function used to do the allocation.
+        *
+        * 1.6.0: The above statement is incorrect; png_handle_tRNS effectively
+        * relies on png_set_tRNS storing the information in png_struct
+        * (otherwise it won't be there for the code in pngrtran.c).
         */
 
        png_free_data(png_ptr, info_ptr, PNG_FREE_TRNS, 0);
 
        /* Changed from num_trans to PNG_MAX_PALETTE_LENGTH in version 1.2.1 */
-       png_ptr->trans_alpha = info_ptr->trans_alpha =
-           (png_bytep)png_malloc(png_ptr, (png_size_t)PNG_MAX_PALETTE_LENGTH);
+       png_ptr->trans_alpha = info_ptr->trans_alpha = png_voidcast(png_bytep,
+         png_malloc(png_ptr, PNG_MAX_PALETTE_LENGTH));
 
        if (num_trans > 0 && num_trans <= PNG_MAX_PALETTE_LENGTH)
           png_memcpy(info_ptr->trans_alpha, trans_alpha, (png_size_t)num_trans);
@@ -910,11 +919,11 @@ png_set_tRNS(png_structrp png_ptr, png_inforp info_ptr,
       int sample_max = (1 << info_ptr->bit_depth);
 
       if ((info_ptr->color_type == PNG_COLOR_TYPE_GRAY &&
-          (int)trans_color->gray > sample_max) ||
+          trans_color->gray > sample_max) ||
           (info_ptr->color_type == PNG_COLOR_TYPE_RGB &&
-          ((int)trans_color->red > sample_max ||
-          (int)trans_color->green > sample_max ||
-          (int)trans_color->blue > sample_max)))
+          (trans_color->red > sample_max ||
+          trans_color->green > sample_max ||
+          trans_color->blue > sample_max)))
          png_warning(png_ptr,
             "tRNS chunk has out-of-range samples for bit_depth");
 
@@ -937,7 +946,7 @@ png_set_tRNS(png_structrp png_ptr, png_inforp info_ptr,
 
 #ifdef PNG_sPLT_SUPPORTED
 void PNGAPI
-png_set_sPLT(png_structrp png_ptr,
+png_set_sPLT(png_const_structrp png_ptr,
     png_inforp info_ptr, png_const_sPLT_tp entries, int nentries)
 /*
  *  entries        - array of png_sPLT_t structures
@@ -1015,7 +1024,7 @@ png_set_sPLT(png_structrp png_ptr,
 
 #ifdef PNG_UNKNOWN_CHUNKS_SUPPORTED
 void PNGAPI
-png_set_unknown_chunks(png_structrp png_ptr,
+png_set_unknown_chunks(png_const_structrp png_ptr,
    png_inforp info_ptr, png_const_unknown_chunkp unknowns, int num_unknowns)
 {
    png_unknown_chunkp np;
@@ -1080,7 +1089,7 @@ png_set_unknown_chunks(png_structrp png_ptr,
 }
 
 void PNGAPI
-png_set_unknown_chunk_location(png_structrp png_ptr, png_inforp info_ptr,
+png_set_unknown_chunk_location(png_const_structrp png_ptr, png_inforp info_ptr,
     int chunk, int location)
 {
    if (png_ptr != NULL && info_ptr != NULL && chunk >= 0 && chunk <
@@ -1097,19 +1106,18 @@ png_permit_mng_features (png_structrp png_ptr, png_uint_32 mng_features)
    png_debug(1, "in png_permit_mng_features");
 
    if (png_ptr == NULL)
-      return (png_uint_32)0;
+      return 0;
 
-   png_ptr->mng_features_permitted =
-       (png_byte)(mng_features & PNG_ALL_MNG_FEATURES);
+   png_ptr->mng_features_permitted = mng_features & PNG_ALL_MNG_FEATURES;
 
-   return (png_uint_32)png_ptr->mng_features_permitted;
+   return png_ptr->mng_features_permitted;
 }
 #endif
 
 #ifdef PNG_HANDLE_AS_UNKNOWN_SUPPORTED
 void PNGAPI
-png_set_keep_unknown_chunks(png_structrp png_ptr, int keep, png_const_bytep
-    chunk_list, int num_chunks)
+png_set_keep_unknown_chunks(png_structrp png_ptr, int keep,
+    png_const_bytep chunk_list, int num_chunks)
 {
    png_bytep new_list, p;
    int i, old_num_chunks;
@@ -1142,14 +1150,12 @@ png_set_keep_unknown_chunks(png_structrp png_ptr, int keep, png_const_bytep
 
    if (png_ptr->chunk_list != NULL)
    {
-      png_memcpy(new_list, png_ptr->chunk_list,
-          (png_size_t)(5*old_num_chunks));
+      png_memcpy(new_list, png_ptr->chunk_list, 5*old_num_chunks);
       png_free(png_ptr, png_ptr->chunk_list);
       png_ptr->chunk_list=NULL;
    }
 
-   png_memcpy(new_list + 5*old_num_chunks, chunk_list,
-       (png_size_t)(5*num_chunks));
+   png_memcpy(new_list + 5*old_num_chunks, chunk_list, 5*num_chunks);
 
    for (p = new_list + 5*old_num_chunks + 4, i = 0; i<num_chunks; i++, p += 5)
       *p=(png_byte)keep;
@@ -1177,7 +1183,8 @@ png_set_read_user_chunk_fn(png_structrp png_ptr, png_voidp user_chunk_ptr,
 
 #ifdef PNG_INFO_IMAGE_SUPPORTED
 void PNGAPI
-png_set_rows(png_structrp png_ptr, png_inforp info_ptr, png_bytepp row_pointers)
+png_set_rows(png_const_structrp png_ptr, png_inforp info_ptr,
+    png_bytepp row_pointers)
 {
    png_debug1(1, "in %s storage function", "rows");
 
@@ -1230,7 +1237,6 @@ png_set_invalid(png_const_structrp png_ptr, png_inforp info_ptr, int mask)
 }
 
 
-
 #ifdef PNG_SET_USER_LIMITS_SUPPORTED
 /* This function was added to libpng 1.2.6 */
 void PNGAPI
@@ -1250,8 +1256,7 @@ png_set_user_limits (png_structrp png_ptr, png_uint_32 user_width_max,
 
 /* This function was added to libpng 1.4.0 */
 void PNGAPI
-png_set_chunk_cache_max (png_structrp png_ptr,
-   png_uint_32 user_chunk_cache_max)
+png_set_chunk_cache_max (png_structrp png_ptr, png_uint_32 user_chunk_cache_max)
 {
     if (png_ptr)
        png_ptr->user_chunk_cache_max = user_chunk_cache_max;
diff --git a/pngstruct.h b/pngstruct.h
index 568c48fb7..1ce804240 100644
--- a/pngstruct.h
+++ b/pngstruct.h
@@ -238,10 +238,6 @@ struct png_struct_def
    png_bytep quantize_index; /* index translation for palette files */
 #endif
 
-#if defined(PNG_READ_QUANTIZE_SUPPORTED) || defined(PNG_hIST_SUPPORTED)
-   png_uint_16p hist;                /* histogram */
-#endif
-
 #ifdef PNG_WRITE_WEIGHTED_FILTER_SUPPORTED
    png_byte heuristic_method;        /* heuristic for row filter selection */
    png_byte num_prev_filters;        /* number of weights for previous rows */