X-Git-Url: http://git.imager.perl.org/imager.git/blobdiff_plain/b51bcea53e36391afe8693d73ba7c691f1855ae4..6494c395d2d9d663dba544b47894ae6bca40dbb0:/PNG/impng.c

diff --git a/PNG/impng.c b/PNG/impng.c
index 6ac9e8c6..c7a7b8e4 100644
--- a/PNG/impng.c
+++ b/PNG/impng.c
@@ -1,5 +1,8 @@
 #include "impng.h"
 #include "png.h"
+#include <stdlib.h>
+#include <string.h>
+#include <zlib.h>
 
 /* this is a way to get number of channels from color space 
  * Color code to channel number */
@@ -20,11 +23,61 @@ read_paletted(png_structp png_ptr, png_infop info_ptr, int channels, i_img_dim w
 static i_img *
 read_bilevel(png_structp png_ptr, png_infop info_ptr, i_img_dim width, i_img_dim height);
 
+static int
+write_direct8(png_structp png_ptr, png_infop info_ptr, i_img *im);
+
+static int
+write_direct16(png_structp png_ptr, png_infop info_ptr, i_img *im);
+
+static int
+write_paletted(png_structp png_ptr, png_infop info_ptr, i_img *im, int bits);
+
+static int
+write_bilevel(png_structp png_ptr, png_infop info_ptr, i_img *im);
+
+static void 
+get_png_tags(i_img *im, png_structp png_ptr, png_infop info_ptr, int bit_depth, int color_type);
+
+static int
+set_png_tags(i_img *im, png_structp png_ptr, png_infop info_ptr);
+
+static const char *
+get_string2(i_img_tags *tags, const char *name, char *buf, size_t *size);
+
 unsigned
 i_png_lib_version(void) {
   return png_access_version_number();
 }
 
+static char const * const
+features[] =
+  {
+#ifdef PNG_BENIGN_ERRORS_SUPPORTED
+    "benign-errors",
+#endif
+#ifdef PNG_READ_SUPPORTED
+    "read",
+#endif
+#ifdef PNG_WRITE_SUPPORTED
+    "write",
+#endif
+#ifdef PNG_MNG_FEATURES_SUPPORTED
+    "mng-features",
+#endif
+#ifdef PNG_CHECK_cHRM_SUPPORTED
+    "check-cHRM",
+#endif
+#ifdef PNG_SET_USER_LIMITS_SUPPORTED
+    "user-limits",
+#endif
+    NULL
+  };
+
+const char * const *
+i_png_features(void) {
+  return features;
+}
+
 static void
 wiol_read_data(png_structp png_ptr, png_bytep data, png_size_t length) {
   io_glue *ig = png_get_io_ptr(png_ptr);
@@ -42,7 +95,9 @@ wiol_write_data(png_structp png_ptr, png_bytep data, png_size_t length) {
 
 static void
 wiol_flush_data(png_structp png_ptr) {
-  /* XXX : This needs to be added to the io layer */
+  io_glue *ig = png_get_io_ptr(png_ptr);
+  if (!i_io_flush(ig))
+    png_error(png_ptr, "Error flushing output");
 }
 
 static void
@@ -72,12 +127,10 @@ undef_int
 i_writepng_wiol(i_img *im, io_glue *ig) {
   png_structp png_ptr;
   png_infop info_ptr = NULL;
-  i_img_dim width,height,y;
+  i_img_dim width,height;
   volatile int cspace,channels;
-  double xres, yres;
-  int aspect_only, have_res;
-  unsigned char *data;
-  unsigned char * volatile vdata = NULL;
+  int bits;
+  int is_bilevel = 0, zero_is_white;
 
   mm_log((1,"i_writepng(im %p ,ig %p)\n", im, ig));
 
@@ -108,13 +161,45 @@ i_writepng_wiol(i_img *im, io_glue *ig) {
 
   channels=im->channels;
 
-  if (channels > 2) { cspace = PNG_COLOR_TYPE_RGB; channels-=3; }
-  else { cspace=PNG_COLOR_TYPE_GRAY; channels--; }
-  
-  if (channels) cspace|=PNG_COLOR_MASK_ALPHA;
-  mm_log((1,"cspace=%d\n",cspace));
+  if (i_img_is_monochrome(im, &zero_is_white)) {
+    is_bilevel = 1;
+    bits = 1;
+    cspace = PNG_COLOR_TYPE_GRAY;
+    mm_log((1, "i_writepng: bilevel output\n"));
+  }
+  else if (im->type == i_palette_type) {
+    int colors = i_colorcount(im);
+
+    cspace = PNG_COLOR_TYPE_PALETTE;
+    bits = 1;
+    while ((1 << bits) < colors) {
+      bits += bits;
+    }
+    mm_log((1, "i_writepng: paletted output\n"));
+  }
+  else {
+    switch (channels) {
+    case 1:
+      cspace = PNG_COLOR_TYPE_GRAY;
+      break;
+    case 2:
+      cspace = PNG_COLOR_TYPE_GRAY_ALPHA;
+      break;
+    case 3:
+      cspace = PNG_COLOR_TYPE_RGB;
+      break;
+    case 4:
+      cspace = PNG_COLOR_TYPE_RGB_ALPHA;
+      break;
+    default:
+      fprintf(stderr, "Internal error, channels = %d\n", channels);
+      abort();
+    }
+    bits = im->bits > 8 ? 16 : 8;
+    mm_log((1, "i_writepng: direct output\n"));
+  }
 
-  channels = im->channels;
+  mm_log((1,"i_writepng: cspace=%d, bits=%d\n",cspace, bits));
 
   /* Create and initialize the png_struct with the desired error handler
    * functions.  If you want to use the default stderr and longjump method,
@@ -142,8 +227,6 @@ i_writepng_wiol(i_img *im, io_glue *ig) {
    */
   if (setjmp(png_jmpbuf(png_ptr))) {
     png_destroy_write_struct(&png_ptr, &info_ptr);
-    if (vdata)
-      myfree(vdata);
     return(0);
   }
   
@@ -164,39 +247,38 @@ i_writepng_wiol(i_img *im, io_glue *ig) {
    */
   png_set_user_limits(png_ptr, width, height);
 
-  png_set_IHDR(png_ptr, info_ptr, width, height, 8, cspace,
+  png_set_IHDR(png_ptr, info_ptr, width, height, bits, cspace,
 	       PNG_INTERLACE_NONE, PNG_COMPRESSION_TYPE_BASE, PNG_FILTER_TYPE_BASE);
 
-  have_res = 1;
-  if (i_tags_get_float(&im->tags, "i_xres", 0, &xres)) {
-    if (i_tags_get_float(&im->tags, "i_yres", 0, &yres))
-      ; /* nothing to do */
-    else
-      yres = xres;
+  if (!set_png_tags(im, png_ptr, info_ptr)) {
+    png_destroy_write_struct(&png_ptr, &info_ptr);
+    return 0;
   }
-  else {
-    if (i_tags_get_float(&im->tags, "i_yres", 0, &yres))
-      xres = yres;
-    else
-      have_res = 0;
+
+  if (is_bilevel) {
+    if (!write_bilevel(png_ptr, info_ptr, im)) {
+      png_destroy_write_struct(&png_ptr, &info_ptr);
+      return 0;
+    }
   }
-  if (have_res) {
-    aspect_only = 0;
-    i_tags_get_int(&im->tags, "i_aspect_only", 0, &aspect_only);
-    xres /= 0.0254;
-    yres /= 0.0254;
-    png_set_pHYs(png_ptr, info_ptr, xres + 0.5, yres + 0.5, 
-                 aspect_only ? PNG_RESOLUTION_UNKNOWN : PNG_RESOLUTION_METER);
+  else if (im->type == i_palette_type) {
+    if (!write_paletted(png_ptr, info_ptr, im, bits)) {
+      png_destroy_write_struct(&png_ptr, &info_ptr);
+      return 0;
+    }
   }
-
-  png_write_info(png_ptr, info_ptr);
-
-  vdata = data = mymalloc(im->xsize * im->channels);
-  for (y = 0; y < height; y++) {
-    i_gsamp(im, 0, im->xsize, y, data, NULL, im->channels);
-    png_write_row(png_ptr, (png_bytep)data);
+  else if (bits == 16) {
+    if (!write_direct16(png_ptr, info_ptr, im)) {
+      png_destroy_write_struct(&png_ptr, &info_ptr);
+      return 0;
+    }
+  }
+  else {
+    if (!write_direct8(png_ptr, info_ptr, im)) {
+      png_destroy_write_struct(&png_ptr, &info_ptr);
+      return 0;
+    }
   }
-  myfree(data);
 
   png_write_end(png_ptr, info_ptr);
 
@@ -208,9 +290,6 @@ i_writepng_wiol(i_img *im, io_glue *ig) {
   return(1);
 }
 
-static void 
-get_png_tags(i_img *im, png_structp png_ptr, png_infop info_ptr, int bit_depth);
-
 typedef struct {
   char *warnings;
 } i_png_read_state, *i_png_read_statep;
@@ -222,7 +301,7 @@ static void
 cleanup_read_state(i_png_read_statep);
 
 i_img*
-i_readpng_wiol(io_glue *ig) {
+i_readpng_wiol(io_glue *ig, int flags) {
   i_img *im = NULL;
   png_structp png_ptr;
   png_infop info_ptr;
@@ -245,7 +324,23 @@ i_readpng_wiol(io_glue *ig) {
     return NULL;
   }
   png_set_read_fn(png_ptr, (png_voidp) (ig), wiol_read_data);
-  
+
+#if defined(PNG_BENIGN_ERRORS_SUPPORTED)
+  png_set_benign_errors(png_ptr, (flags & IMPNG_READ_IGNORE_BENIGN_ERRORS) ? 1 : 0);
+#elif PNG_LIBPNG_VER >= 10400
+  if (flags & IMPNG_READ_IGNORE_BENIGN_ERRORS) {
+    i_push_error(0, "libpng not configured to ignore benign errors");
+    png_destroy_read_struct(&png_ptr, (png_infopp)NULL, (png_infopp)NULL);
+    return NULL;
+  }
+#else
+  if (flags & IMPNG_READ_IGNORE_BENIGN_ERRORS) {
+    i_push_error(0, "libpng too old to ignore benign errors");
+    png_destroy_read_struct(&png_ptr, (png_infopp)NULL, (png_infopp)NULL);
+    return NULL;
+  }
+#endif
+
   info_ptr = png_create_info_struct(png_ptr);
   if (info_ptr == NULL) {
     png_destroy_read_struct(&png_ptr, (png_infopp)NULL, (png_infopp)NULL);
@@ -260,7 +355,7 @@ i_readpng_wiol(io_glue *ig) {
     cleanup_read_state(&rs);
     return NULL;
   }
-  
+
   /* we do our own limit checks */
   png_set_user_limits(png_ptr, PNG_DIM_MAX, PNG_DIM_MAX);
 
@@ -268,9 +363,8 @@ i_readpng_wiol(io_glue *ig) {
   png_read_info(png_ptr, info_ptr);
   png_get_IHDR(png_ptr, info_ptr, &width, &height, &bit_depth, &color_type, &interlace_type, NULL, NULL);
   
-  mm_log((1,
-	  "png_get_IHDR results: width %d, height %d, bit_depth %d, color_type %d, interlace_type %d\n",
-	  width,height,bit_depth,color_type,interlace_type));
+  mm_log((1, "png_get_IHDR results: width %u, height %u, bit_depth %d, color_type %d, interlace_type %d\n",
+	  (unsigned)width, (unsigned)height, bit_depth,color_type,interlace_type));
   
   CC2C[PNG_COLOR_TYPE_GRAY]=1;
   CC2C[PNG_COLOR_TYPE_PALETTE]=3;
@@ -303,7 +397,7 @@ i_readpng_wiol(io_glue *ig) {
   }
 
   if (im)
-    get_png_tags(im, png_ptr, info_ptr, bit_depth);
+    get_png_tags(im, png_ptr, info_ptr, bit_depth, color_type);
 
   png_destroy_read_struct(&png_ptr, &info_ptr, (png_infopp)NULL);
 
@@ -617,14 +711,29 @@ text_tags[] = {
 
 static const int text_tags_count = sizeof(text_tags) / sizeof(*text_tags);
 
+static const char * const
+chroma_tags[] = {
+  "png_chroma_white_x",
+  "png_chroma_white_y",
+  "png_chroma_red_x",
+  "png_chroma_red_y",
+  "png_chroma_green_x",
+  "png_chroma_green_y",
+  "png_chroma_blue_x",
+  "png_chroma_blue_y"
+};
+
+static const int chroma_tag_count = sizeof(chroma_tags) / sizeof(*chroma_tags);
+
 static void
-get_png_tags(i_img *im, png_structp png_ptr, png_infop info_ptr, int bit_depth) {
+get_png_tags(i_img *im, png_structp png_ptr, png_infop info_ptr,
+	     int bit_depth, int color_type) {
   png_uint_32 xres, yres;
   int unit_type;
 
   i_tags_set(&im->tags, "i_format", "png", -1);
   if (png_get_pHYs(png_ptr, info_ptr, &xres, &yres, &unit_type)) {
-    mm_log((1,"pHYs (%d, %d) %d\n", xres, yres, unit_type));
+    mm_log((1,"pHYs (%u, %u) %d\n", (unsigned)xres, (unsigned)yres, unit_type));
     if (unit_type == PNG_RESOLUTION_METER) {
       i_tags_set_float2(&im->tags, "i_xres", 0, xres * 0.0254, 5);
       i_tags_set_float2(&im->tags, "i_yres", 0, yres * 0.0254, 5);
@@ -657,36 +766,32 @@ get_png_tags(i_img *im, png_structp png_ptr, png_infop info_ptr, int bit_depth)
   /* the various readers can call png_set_expand(), libpng will make
      it's internal record of bit_depth at least 8 in that case */
   i_tags_setn(&im->tags, "png_bits", bit_depth);
-
   
-  {
+  if (png_get_valid(png_ptr, info_ptr, PNG_INFO_sRGB)) {
     int intent;
     if (png_get_sRGB(png_ptr, info_ptr, &intent)) {
       i_tags_setn(&im->tags, "png_srgb_intent", intent);
     }
   }
-  {
+  else {
+    /* Ignore these if there's an sRGB chunk, libpng simulates
+       their existence if there's an sRGB chunk, and the PNG spec says
+       that these are ignored if the sRGB is present, so ignore them.
+    */
     double gamma;
+    double chroma[8];
+
     if (png_get_gAMA(png_ptr, info_ptr, &gamma)) {
       i_tags_set_float2(&im->tags, "png_gamma", 0, gamma, 4);
     }
-  }
-  {
-    double white_x, white_y;
-    double red_x, red_y;
-    double green_x, green_y;
-    double blue_x, blue_y;
-    if (png_get_cHRM(png_ptr, info_ptr, &white_x, &white_y,
-		     &red_x, &red_y, &green_x, &green_y,
-		     &blue_x, &blue_y)) {
-      i_tags_set_float2(&im->tags, "png_chroma_white_x", 0, white_x, 4);
-      i_tags_set_float2(&im->tags, "png_chroma_white_y", 0, white_y, 4);
-      i_tags_set_float2(&im->tags, "png_chroma_red_x", 0, red_x, 4);
-      i_tags_set_float2(&im->tags, "png_chroma_red_y", 0, red_y, 4);
-      i_tags_set_float2(&im->tags, "png_chroma_green_x", 0, green_x, 4);
-      i_tags_set_float2(&im->tags, "png_chroma_green_y", 0, green_y, 4);
-      i_tags_set_float2(&im->tags, "png_chroma_blue_x", 0, blue_x, 4);
-      i_tags_set_float2(&im->tags, "png_chroma_blue_y", 0, blue_y, 4);
+
+    if (png_get_cHRM(png_ptr, info_ptr, chroma+0, chroma+1,
+		     chroma+2, chroma+3, chroma+4, chroma+5,
+		     chroma+6, chroma+7)) {
+      int i;
+
+      for (i = 0; i < chroma_tag_count; ++i)
+	i_tags_set_float2(&im->tags, chroma_tags[i], 0, chroma[i], 4);
     }
   }
 
@@ -696,30 +801,561 @@ get_png_tags(i_img *im, png_structp png_ptr, png_infop info_ptr, int bit_depth)
 
     if (png_get_text(png_ptr, info_ptr, &text, &num_text)) {
       int i;
+      int custom_index = 0;
       for (i = 0; i < num_text; ++i) {
 	int j;
-	char tag_name[50];
-	sprintf(tag_name, "png_text%d_key", i);
-	i_tags_set(&im->tags, tag_name, text[i].key, -1);
-	sprintf(tag_name, "png_text%d_text", i);
-	i_tags_set(&im->tags, tag_name, text[i].text, -1);
-	sprintf(tag_name, "png_text%d_type", i);
-	i_tags_set(&im->tags, tag_name, 
-		   (text[i].compression == PNG_TEXT_COMPRESSION_NONE
-		    || text[i].compression == PNG_TEXT_COMPRESSION_zTXt) ?
-		   "text" : "itxt", -1);
+	int found = 0;
+	int compressed = text[i].compression == PNG_ITXT_COMPRESSION_zTXt
+	  || text[i].compression == PNG_TEXT_COMPRESSION_zTXt;
 
 	for (j = 0; j < text_tags_count; ++j) {
 	  if (strcmp(text_tags[j].keyword, text[i].key) == 0) {
+	    char tag_name[50];
 	    i_tags_set(&im->tags, text_tags[j].tagname, text[i].text, -1);
+	    if (compressed) {
+	      sprintf(tag_name, "%s_compressed", text_tags[j].tagname);
+	      i_tags_setn(&im->tags, tag_name, 1);
+	    }
+	    found = 1;
+	    break;
+	  }
+	}
+
+	if (!found) {
+	  char tag_name[50];
+	  sprintf(tag_name, "png_text%d_key", custom_index);
+	  i_tags_set(&im->tags, tag_name, text[i].key, -1);
+	  sprintf(tag_name, "png_text%d_text", custom_index);
+	  i_tags_set(&im->tags, tag_name, text[i].text, -1);
+	  sprintf(tag_name, "png_text%d_type", custom_index);
+	  i_tags_set(&im->tags, tag_name, 
+		     (text[i].compression == PNG_TEXT_COMPRESSION_NONE
+		      || text[i].compression == PNG_TEXT_COMPRESSION_zTXt) ?
+		     "text" : "itxt", -1);
+	  if (compressed) {
+	    sprintf(tag_name, "png_text%d_compressed", custom_index);
+	    i_tags_setn(&im->tags, tag_name, 1);
+	  }
+	  ++custom_index;
+	}
+      }
+    }
+  }
+
+  {
+    png_time *mod_time;
+
+    if (png_get_tIME(png_ptr, info_ptr, &mod_time)) {
+      char time_formatted[80];
+
+      sprintf(time_formatted, "%d-%02d-%02dT%02d:%02d:%02d",
+	      mod_time->year, mod_time->month, mod_time->day,
+	      mod_time->hour, mod_time->minute, mod_time->second);
+      i_tags_set(&im->tags, "png_time", time_formatted, -1);
+    }
+  }
+
+  {
+    png_color_16 *back;
+    i_color c;
+
+    if (png_get_bKGD(png_ptr, info_ptr, &back)) {
+      switch (color_type) {
+      case PNG_COLOR_TYPE_GRAY:
+      case PNG_COLOR_TYPE_GRAY_ALPHA:
+	{
+	  /* lib png stores the raw gray value rather than scaling it
+	     to 16-bit (or 8), we use 8-bit color for i_background */
+
+	  int gray;
+	  switch (bit_depth) {
+	  case 16:
+	    gray = back->gray >> 8;
+	    break;
+	  case 8:
+	    gray = back->gray;
+	    break;
+	  case 4:
+	    gray = 0x11 * back->gray;
+	    break;
+	  case 2:
+	    gray = 0x55 * back->gray;
+	    break;
+	  case 1:
+	    gray = back->gray ? 0xFF : 0;
 	    break;
+	  default:
+	    gray = 0;
 	  }
+	  c.rgb.r = c.rgb.g = c.rgb.b = gray;
+	  break;
 	}
+
+      case PNG_COLOR_TYPE_RGB:
+      case PNG_COLOR_TYPE_RGB_ALPHA:
+	{
+	  c.rgb.r = bit_depth == 16 ? (back->red   >> 8) : back->red;
+	  c.rgb.g = bit_depth == 16 ? (back->green >> 8) : back->green;
+	  c.rgb.b = bit_depth == 16 ? (back->blue  >> 8) : back->blue;
+	  break;
+	}
+
+      case PNG_COLOR_TYPE_PALETTE:
+	c.rgb.r = back->red;
+	c.rgb.g = back->green;
+	c.rgb.b = back->blue;
+	break;
       }
+
+      c.rgba.a = 255;
+      i_tags_set_color(&im->tags, "i_background", 0, &c);
     }
   }
 }
 
+#define GET_STR_BUF_SIZE 40
+
+static int
+set_png_tags(i_img *im, png_structp png_ptr, png_infop info_ptr) {
+  double xres, yres;
+  int aspect_only, have_res = 1;
+
+  if (i_tags_get_float(&im->tags, "i_xres", 0, &xres)) {
+    if (i_tags_get_float(&im->tags, "i_yres", 0, &yres))
+      ; /* nothing to do */
+    else
+      yres = xres;
+  }
+  else {
+    if (i_tags_get_float(&im->tags, "i_yres", 0, &yres))
+      xres = yres;
+    else
+      have_res = 0;
+  }
+  if (have_res) {
+    aspect_only = 0;
+    i_tags_get_int(&im->tags, "i_aspect_only", 0, &aspect_only);
+    xres /= 0.0254;
+    yres /= 0.0254;
+    png_set_pHYs(png_ptr, info_ptr, xres + 0.5, yres + 0.5, 
+                 aspect_only ? PNG_RESOLUTION_UNKNOWN : PNG_RESOLUTION_METER);
+  }
+
+  {
+    int intent;
+    if (i_tags_get_int(&im->tags, "png_srgb_intent", 0, &intent)) {
+      if (intent < 0 || intent >= PNG_sRGB_INTENT_LAST) {
+	i_push_error(0, "tag png_srgb_intent out of range");
+	return 0;
+      }
+      png_set_sRGB(png_ptr, info_ptr, intent);
+    }
+    else {
+      double chroma[8], gamma;
+      int i;
+      int found_chroma_count = 0;
+
+      for (i = 0; i < chroma_tag_count; ++i) {
+	if (i_tags_get_float(&im->tags, chroma_tags[i], 0, chroma+i))
+	  ++found_chroma_count;
+      }
+
+      if (found_chroma_count) {
+	if (found_chroma_count != chroma_tag_count) {
+	  i_push_error(0, "all png_chroma_* tags must be supplied or none");
+	  return 0;
+	}
+
+	png_set_cHRM(png_ptr, info_ptr, chroma[0], chroma[1], chroma[2],
+		     chroma[3], chroma[4], chroma[5], chroma[6], chroma[7]);
+      }
+
+      if (i_tags_get_float(&im->tags, "png_gamma", 0, &gamma)) {
+	png_set_gAMA(png_ptr, info_ptr, gamma);
+      }
+    }
+  }
+
+  {
+    /* png_set_text() is sparsely documented, it isn't indicated whether
+       multiple calls add to or replace the lists of texts, and
+       whether the text/keyword data is copied or not.
+
+       Examining the linpng code reveals that png_set_text() adds to
+       the list and that the text is copied.
+    */
+    int i;
+
+    /* do our standard tags */
+    for (i = 0; i < text_tags_count; ++i) {
+      char buf[GET_STR_BUF_SIZE];
+      size_t size;
+      const char *data;
+      
+      data = get_string2(&im->tags, text_tags[i].tagname, buf, &size);
+      if (data) {
+	png_text text;
+	int compression = size > 1000;
+	char compress_tag[40];
+
+	if (memchr(data, '\0',  size)) {
+	  i_push_errorf(0, "tag %s may not contain NUL characters", text_tags[i].tagname);
+	  return 0;
+	}
+      
+	sprintf(compress_tag, "%s_compressed", text_tags[i].tagname);
+	i_tags_get_int(&im->tags, compress_tag, 0, &compression);
+	
+	text.compression = compression ? PNG_TEXT_COMPRESSION_zTXt
+	  : PNG_TEXT_COMPRESSION_NONE;
+	text.key = (char *)text_tags[i].keyword;
+	text.text_length = size;
+	text.text = (char *)data;
+#ifdef PNG_iTXt_SUPPORTED
+	text.itxt_length = 0;
+	text.lang = NULL;
+	text.lang_key = NULL;
+#endif
+
+	png_set_text(png_ptr, info_ptr, &text, 1);
+      }
+    }
+
+    /* for non-standard tags ensure keywords are limited to 1 to 79
+       characters */
+    i = 0;
+    while (1) {
+      char tag_name[50];
+      char key_buf[GET_STR_BUF_SIZE], value_buf[GET_STR_BUF_SIZE];
+      const char *key, *value;
+      size_t key_size, value_size;
+
+      sprintf(tag_name, "png_text%d_key", i);
+      key = get_string2(&im->tags, tag_name, key_buf, &key_size);
+      
+      if (key) {
+	size_t k;
+	if (key_size < 1 || key_size > 79) {
+	  i_push_errorf(0, "tag %s must be between 1 and 79 characters in length", tag_name);
+	  return 0;
+	}
+
+	if (key[0] == ' ' || key[key_size-1] == ' ') {
+	  i_push_errorf(0, "tag %s may not contain leading or trailing spaces", tag_name);
+	  return 0;
+	}
+
+	if (strstr(key, "  ")) {
+	  i_push_errorf(0, "tag %s may not contain consecutive spaces", tag_name);
+	  return 0;
+	}
+
+	for (k = 0; k < key_size; ++k) {
+	  if (key[k] < 32 || (key[k] > 126 && key[k] < 161)) {
+	    i_push_errorf(0, "tag %s may only contain Latin1 characters 32-126, 161-255", tag_name);
+	    return 0;
+	  }
+	}
+      }
+
+      sprintf(tag_name, "png_text%d_text", i);
+      value = get_string2(&im->tags, tag_name, value_buf, &value_size);
+
+      if (value) {
+	if (memchr(value, '\0', value_size)) {
+	  i_push_errorf(0, "tag %s may not contain NUL characters", tag_name);
+	  return 0;
+	}
+      }
+
+      if (key && value) {
+	png_text text;
+	int compression = value_size > 1000;
+
+	sprintf(tag_name, "png_text%d_compressed", i);
+	i_tags_get_int(&im->tags, tag_name, 0, &compression);
+
+	text.compression = compression ? PNG_TEXT_COMPRESSION_zTXt
+	  : PNG_TEXT_COMPRESSION_NONE;
+	text.key = (char *)key;
+	text.text_length = value_size;
+	text.text = (char *)value;
+#ifdef PNG_iTXt_SUPPORTED
+	text.itxt_length = 0;
+	text.lang = NULL;
+	text.lang_key = NULL;
+#endif
+
+	png_set_text(png_ptr, info_ptr, &text, 1);
+      }
+      else if (key) {
+	i_push_errorf(0, "tag png_text%d_key found but not png_text%d_text", i, i);
+	return 0;
+      }
+      else if (value) {
+	i_push_errorf(0, "tag png_text%d_text found but not png_text%d_key", i, i);
+	return 0;
+      }
+      else {
+	break;
+      }
+      ++i;
+    }
+  }
+
+  {
+    char buf[GET_STR_BUF_SIZE];
+    size_t time_size;
+    const char *timestr = get_string2(&im->tags, "png_time", buf, &time_size);
+
+    if (timestr) {
+      int year, month, day, hour, minute, second;
+      png_time mod_time;
+
+      if (sscanf(timestr, "%d-%d-%dT%d:%d:%d", &year, &month, &day, &hour, &minute, &second) == 6) {
+	/* rough validation */
+	if (month < 1 || month > 12
+	    || day < 1 || day > 31
+	    || hour < 0 || hour > 23
+	    || minute < 0 || minute > 59
+	    || second < 0 || second > 60) {
+	  i_push_error(0, "invalid date/time for png_time");
+	  return 0;
+	}
+	mod_time.year = year;
+	mod_time.month = month;
+	mod_time.day = day;
+	mod_time.hour = hour;
+	mod_time.minute = minute;
+	mod_time.second = second;
+
+	png_set_tIME(png_ptr, info_ptr, &mod_time);
+      }
+      else {
+	i_push_error(0, "png_time must be formatted 'y-m-dTh:m:s'");
+	return 0;
+      }
+    }
+  }
+
+  {
+    int level;
+    if (i_tags_get_int(&im->tags, "png_compression_level", 0, &level)) {
+      if (level >= Z_NO_COMPRESSION && level <= Z_BEST_COMPRESSION) 
+	png_set_compression_level(png_ptr, level);
+      else {
+	i_push_errorf(0, "png_compression_level must be between %d and %d",
+		      Z_NO_COMPRESSION, Z_BEST_COMPRESSION);
+	return 0;
+      }
+    }
+  }
+
+  {
+    /* no bKGD support yet, maybe later
+       it may be simpler to do it in the individual writers
+     */
+  }
+
+  return 1;
+}
+
+static const char *
+get_string2(i_img_tags *tags, const char *name, char *buf, size_t *size) {
+  int index;
+
+  if (i_tags_find(tags, name, 0, &index)) {
+    const i_img_tag *entry = tags->tags + index;
+    
+    if (entry->data) {
+      *size = entry->size;
+
+      return entry->data;
+    }
+    else {
+      *size = sprintf(buf, "%d", entry->idata);
+
+      return buf;
+    }
+  }
+  return NULL;
+}
+
+static int
+write_direct8(png_structp png_ptr, png_infop info_ptr, i_img *im) {
+  unsigned char *data, *volatile vdata = NULL;
+  i_img_dim y;
+
+  if (setjmp(png_jmpbuf(png_ptr))) {
+    if (vdata)
+      myfree(vdata);
+
+    return 0;
+  }
+
+  png_write_info(png_ptr, info_ptr);
+
+  vdata = data = mymalloc(im->xsize * im->channels);
+  for (y = 0; y < im->ysize; y++) {
+    i_gsamp(im, 0, im->xsize, y, data, NULL, im->channels);
+    png_write_row(png_ptr, (png_bytep)data);
+  }
+  myfree(data);
+
+  return 1;
+}
+
+static int
+write_direct16(png_structp png_ptr, png_infop info_ptr, i_img *im) {
+  unsigned *data, *volatile vdata = NULL;
+  unsigned char *tran_data, * volatile vtran_data = NULL;
+  i_img_dim samples_per_row = im->xsize * im->channels;
+  
+  i_img_dim y;
+
+  if (setjmp(png_jmpbuf(png_ptr))) {
+    if (vdata)
+      myfree(vdata);
+    if (vtran_data)
+      myfree(vtran_data);
+
+    return 0;
+  }
+
+  png_write_info(png_ptr, info_ptr);
+
+  vdata = data = mymalloc(samples_per_row * sizeof(unsigned));
+  vtran_data = tran_data = mymalloc(samples_per_row * 2);
+  for (y = 0; y < im->ysize; y++) {
+    i_img_dim i;
+    unsigned char *p = tran_data;
+    i_gsamp_bits(im, 0, im->xsize, y, data, NULL, im->channels, 16);
+    for (i = 0; i < samples_per_row; ++i) {
+      p[0] = data[i] >> 8;
+      p[1] = data[i] & 0xff;
+      p += 2;
+    }
+    png_write_row(png_ptr, (png_bytep)tran_data);
+  }
+  myfree(tran_data);
+  myfree(data);
+
+  return 1;
+}
+
+static int
+write_paletted(png_structp png_ptr, png_infop info_ptr, i_img *im, int bits) {
+  unsigned char *data, *volatile vdata = NULL;
+  i_img_dim y;
+  unsigned char pal_map[256];
+  png_color pcolors[256];
+  i_color colors[256];
+  int count = i_colorcount(im);
+  int i;
+
+  if (setjmp(png_jmpbuf(png_ptr))) {
+    if (vdata)
+      myfree(vdata);
+
+    return 0;
+  }
+
+  i_getcolors(im, 0, colors, count);
+  if (im->channels < 3) {
+    /* convert the greyscale palette to color */
+    int i;
+    for (i = 0; i < count; ++i) {
+      i_color *c = colors + i;
+      c->channel[3] = c->channel[1];
+      c->channel[2] = c->channel[1] = c->channel[0];
+    }
+  }
+
+  if (i_img_has_alpha(im)) {
+    int i;
+    int bottom_index = 0, top_index = count-1;
+
+    /* fill out the palette map */
+    for (i = 0; i < count; ++i)
+      pal_map[i] = i;
+
+    /* the PNG spec suggests sorting the palette by alpha, but that's
+       unnecessary - all we want to do is move the opaque entries to
+       the end */
+    while (bottom_index < top_index) {
+      if (colors[bottom_index].rgba.a == 255) {
+	pal_map[bottom_index] = top_index;
+	pal_map[top_index--] = bottom_index;
+      }
+      ++bottom_index;
+    }
+  }
+
+  for (i = 0; i < count; ++i) {
+    int srci = i_img_has_alpha(im) ? pal_map[i] : i;
+
+    pcolors[i].red = colors[srci].rgb.r;
+    pcolors[i].green = colors[srci].rgb.g;
+    pcolors[i].blue = colors[srci].rgb.b;
+  }
+
+  png_set_PLTE(png_ptr, info_ptr, pcolors, count);
+
+  if (i_img_has_alpha(im)) {
+    unsigned char trans[256];
+    int i;
+
+    for (i = 0; i < count && colors[pal_map[i]].rgba.a != 255; ++i) {
+      trans[i] = colors[pal_map[i]].rgba.a;
+    }
+    png_set_tRNS(png_ptr, info_ptr, trans, i, NULL);
+  }
+
+  png_write_info(png_ptr, info_ptr);
+
+  png_set_packing(png_ptr);
+
+  vdata = data = mymalloc(im->xsize);
+  for (y = 0; y < im->ysize; y++) {
+    i_gpal(im, 0, im->xsize, y, data);
+    if (i_img_has_alpha(im)) {
+      i_img_dim x;
+      for (x = 0; x < im->xsize; ++x)
+	data[x] = pal_map[data[x]];
+    }
+    png_write_row(png_ptr, (png_bytep)data);
+  }
+  myfree(data);
+
+  return 1;
+}
+
+static int
+write_bilevel(png_structp png_ptr, png_infop info_ptr, i_img *im) {
+  unsigned char *data, *volatile vdata = NULL;
+  i_img_dim y;
+
+  if (setjmp(png_jmpbuf(png_ptr))) {
+    if (vdata)
+      myfree(vdata);
+
+    return 0;
+  }
+
+  png_write_info(png_ptr, info_ptr);
+
+  png_set_packing(png_ptr);
+
+  vdata = data = mymalloc(im->xsize);
+  for (y = 0; y < im->ysize; y++) {
+    i_gsamp(im, 0, im->xsize, y, data, NULL, 1);
+    png_write_row(png_ptr, (png_bytep)data);
+  }
+  myfree(data);
+
+  return 1;
+}
+
 static void
 read_warn_handler(png_structp png_ptr, png_const_charp msg) {
   i_png_read_statep rs = (i_png_read_statep)png_get_error_ptr(png_ptr);