diff --git a/bitblt_g4.c b/bitblt_g4.c
index 5a82122..b4ad2ab 100644
--- a/bitblt_g4.c
+++ b/bitblt_g4.c
@@ -4,7 +4,7 @@
  *      will be compressed using ITU-T T.6 (G4) fax encoding.
  *
  * PDF routines
- * $Id: bitblt_g4.c,v 1.5 2003/02/21 01:25:47 eric Exp $
+ * $Id: bitblt_g4.c,v 1.6 2003/02/21 02:49:11 eric Exp $
  * Copyright 2001, 2002, 2003 Eric Smith <eric@brouhaha.com>
  *
  * This program is free software; you can redistribute it and/or modify
@@ -27,6 +27,7 @@
 #include <stdbool.h>
 #include <stdint.h>
 #include <stdio.h>
+#include <stdlib.h>
 #include <string.h>
 
 
@@ -37,6 +38,9 @@
 #include "pdf_private.h"
 
 
+#define SWAP(type,a,b) do { type temp; temp = a; a = b; b = temp; } while (0)
+
+
 struct pdf_g4_image
 {
   double width, height;
@@ -94,28 +98,48 @@ void pdf_write_g4_fax_image_callback (pdf_file_handle pdf_file,
 {
   struct pdf_g4_image *image = app_data;
 
-#if 0
-  pdf_stream_write_data (pdf_file, stream, image->data, image->len);
-#else
-  unsigned long row = 0;
-  word_type *ref;
-  word_type *raw;
+  uint32_t row;
 
-  ref = NULL;
-  raw = image->bitmap->bits;
+  /* reference (previous) row */
+  uint32_t *ref_runs = pdf_calloc (image->Columns, sizeof (uint32_t));
+  uint32_t ref_run_count;
 
-  while (row < image->Rows)
+  /* row being converted */
+  uint32_t *row_runs = pdf_calloc (image->Columns, sizeof (uint32_t));
+  uint32_t row_run_count;
+
+  /* initialize reference row - all white */
+  ref_runs [0] = image->Columns;
+  ref_run_count = 0;
+
+  for (row = image->bitmap->rect.min.y;
+       row < image->bitmap->rect.max.y;
+       row++)
     {
-      pdf_stream_write_data (pdf_file, stream, (uint8_t *) raw,
-			     image->bitmap->row_words * sizeof (word_type));
+      row_run_count = get_row_run_lengths (image->bitmap,
+					   row,
+					   image->bitmap->rect.min.x,
+					   image->bitmap->rect.max.x - 1,
+					   image->Columns,  /* max_runs */
+					   row_runs);
+      pdf_assert (row_run_count > 0);
 
-      row++;
-      ref = raw;
-      raw += image->bitmap->row_words;
+      /* $$$ G4 encode the runs here */
+
+      /* pdf_stream_write_data (pdf_file, stream, image->data, image->len); */
+
+      SWAP (uint32_t *, row_runs, ref_runs);
+      ref_run_count = row_run_count;
     }
+
+  
   /* $$$ generate and write EOFB code */
-  /* $$$ flush any remaining buffered bits */
-#endif
+  pdf_stream_write_bits (pdf_file, stream, 24, 0x001001);
+
+  pdf_stream_flush_bits (pdf_file, stream);
+
+  free (ref_runs);
+  free (row_runs);
 }
 
 
@@ -139,7 +163,7 @@ void pdf_write_g4_fax_image (pdf_page_handle pdf_page,
 
   struct pdf_obj *content_stream;
 
-  image = pdf_calloc (sizeof (struct pdf_g4_image));
+  image = pdf_calloc (1, sizeof (struct pdf_g4_image));
 
   image->width = width;
   image->height = height;
diff --git a/pdf.c b/pdf.c
index 4033c82..6dd5f55 100644
--- a/pdf.c
+++ b/pdf.c
@@ -4,7 +4,7 @@
  *      will be compressed using ITU-T T.6 (G4) fax encoding.
  *
  * PDF routines
- * $Id: pdf.c,v 1.3 2003/02/20 04:44:17 eric Exp $
+ * $Id: pdf.c,v 1.4 2003/02/21 02:49:11 eric Exp $
  * Copyright 2001, 2002, 2003 Eric Smith <eric@brouhaha.com>
  *
  * This program is free software; you can redistribute it and/or modify
@@ -53,7 +53,7 @@ void pdf_init (void)
 
 struct pdf_pages *pdf_new_pages (pdf_file_handle pdf_file)
 {
-  struct pdf_pages *pages = pdf_calloc (sizeof (struct pdf_pages));
+  struct pdf_pages *pages = pdf_calloc (1, sizeof (struct pdf_pages));
   pages->kids = pdf_new_ind_ref (pdf_file, pdf_new_obj (PT_ARRAY));
   pages->count = pdf_new_integer (0);
   pages->pages_dict = pdf_new_ind_ref (pdf_file, pdf_new_obj (PT_DICTIONARY));
@@ -68,7 +68,7 @@ pdf_file_handle pdf_create (char *filename)
 {
   pdf_file_handle pdf_file;
 
-  pdf_file = pdf_calloc (sizeof (struct pdf_file));
+  pdf_file = pdf_calloc (1, sizeof (struct pdf_file));
 
   pdf_file->f = fopen (filename, "wb");
   if (! pdf_file->f)
@@ -154,7 +154,7 @@ pdf_page_handle pdf_new_page (pdf_file_handle pdf_file,
 			      double width,
 			      double height)
 {
-  pdf_page_handle page = pdf_calloc (sizeof (struct pdf_page));
+  pdf_page_handle page = pdf_calloc (1, sizeof (struct pdf_page));
 
   page->pdf_file = pdf_file;
 
diff --git a/pdf_g4.c b/pdf_g4.c
index eef5e68..cdbd8ec 100644
--- a/pdf_g4.c
+++ b/pdf_g4.c
@@ -4,7 +4,7 @@
  *      will be compressed using ITU-T T.6 (G4) fax encoding.
  *
  * PDF routines
- * $Id: pdf_g4.c,v 1.5 2003/02/21 01:25:47 eric Exp $
+ * $Id: pdf_g4.c,v 1.6 2003/02/21 02:49:11 eric Exp $
  * Copyright 2001, 2002, 2003 Eric Smith <eric@brouhaha.com>
  *
  * This program is free software; you can redistribute it and/or modify
@@ -27,6 +27,7 @@
 #include <stdbool.h>
 #include <stdint.h>
 #include <stdio.h>
+#include <stdlib.h>
 #include <string.h>
 
 
@@ -37,6 +38,9 @@
 #include "pdf_private.h"
 
 
+#define SWAP(type,a,b) do { type temp; temp = a; a = b; b = temp; } while (0)
+
+
 struct pdf_g4_image
 {
   double width, height;
@@ -94,28 +98,48 @@ void pdf_write_g4_fax_image_callback (pdf_file_handle pdf_file,
 {
   struct pdf_g4_image *image = app_data;
 
-#if 0
-  pdf_stream_write_data (pdf_file, stream, image->data, image->len);
-#else
-  unsigned long row = 0;
-  word_type *ref;
-  word_type *raw;
+  uint32_t row;
 
-  ref = NULL;
-  raw = image->bitmap->bits;
+  /* reference (previous) row */
+  uint32_t *ref_runs = pdf_calloc (image->Columns, sizeof (uint32_t));
+  uint32_t ref_run_count;
 
-  while (row < image->Rows)
+  /* row being converted */
+  uint32_t *row_runs = pdf_calloc (image->Columns, sizeof (uint32_t));
+  uint32_t row_run_count;
+
+  /* initialize reference row - all white */
+  ref_runs [0] = image->Columns;
+  ref_run_count = 0;
+
+  for (row = image->bitmap->rect.min.y;
+       row < image->bitmap->rect.max.y;
+       row++)
     {
-      pdf_stream_write_data (pdf_file, stream, (uint8_t *) raw,
-			     image->bitmap->row_words * sizeof (word_type));
+      row_run_count = get_row_run_lengths (image->bitmap,
+					   row,
+					   image->bitmap->rect.min.x,
+					   image->bitmap->rect.max.x - 1,
+					   image->Columns,  /* max_runs */
+					   row_runs);
+      pdf_assert (row_run_count > 0);
 
-      row++;
-      ref = raw;
-      raw += image->bitmap->row_words;
+      /* $$$ G4 encode the runs here */
+
+      /* pdf_stream_write_data (pdf_file, stream, image->data, image->len); */
+
+      SWAP (uint32_t *, row_runs, ref_runs);
+      ref_run_count = row_run_count;
     }
+
+  
   /* $$$ generate and write EOFB code */
-  /* $$$ flush any remaining buffered bits */
-#endif
+  pdf_stream_write_bits (pdf_file, stream, 24, 0x001001);
+
+  pdf_stream_flush_bits (pdf_file, stream);
+
+  free (ref_runs);
+  free (row_runs);
 }
 
 
@@ -139,7 +163,7 @@ void pdf_write_g4_fax_image (pdf_page_handle pdf_page,
 
   struct pdf_obj *content_stream;
 
-  image = pdf_calloc (sizeof (struct pdf_g4_image));
+  image = pdf_calloc (1, sizeof (struct pdf_g4_image));
 
   image->width = width;
   image->height = height;
diff --git a/pdf_prim.c b/pdf_prim.c
index bbf6ddf..e0f2c3c 100644
--- a/pdf_prim.c
+++ b/pdf_prim.c
@@ -4,7 +4,7 @@
  *      will be compressed using ITU-T T.6 (G4) fax encoding.
  *
  * PDF routines
- * $Id: pdf_prim.c,v 1.4 2003/02/21 01:25:47 eric Exp $
+ * $Id: pdf_prim.c,v 1.5 2003/02/21 02:49:11 eric Exp $
  * Copyright 2001, 2002, 2003 Eric Smith <eric@brouhaha.com>
  *
  * This program is free software; you can redistribute it and/or modify
@@ -66,6 +66,8 @@ struct pdf_dict
 };
 
 
+#define STREAM_BUF_SIZE 4096
+
 struct pdf_stream
 {
   struct pdf_obj *stream_dict;
@@ -74,6 +76,13 @@ struct pdf_stream
   void *app_data;  /* arg to pass to callback */
   struct pdf_obj *filters;  /* name or array of names */
   struct pdf_obj *decode_parms;
+
+  /* The following fields are used by pdf_stream_write_bits() and
+     pdf_stream_flush_bits(). */
+  uint32_t byte_idx;  /* index to next byte position in data buffer */
+  uint32_t bit_idx;   /* index to next bit position in data buffer,
+			 0 = MSB, 7 = LSB */
+  uint8_t data [STREAM_BUF_SIZE];
 };
 
 
@@ -145,7 +154,7 @@ void pdf_set_dict_entry (struct pdf_obj *dict_obj, char *key, struct pdf_obj *va
       }
 
   /* new entry */
-  entry = pdf_calloc (sizeof (struct pdf_dict_entry));
+  entry = pdf_calloc (1, sizeof (struct pdf_dict_entry));
 
   entry->next = dict_obj->val.dict.first;
   dict_obj->val.dict.first = entry;
@@ -174,7 +183,7 @@ struct pdf_obj *pdf_get_dict_entry (struct pdf_obj *dict_obj, char *key)
 
 void pdf_add_array_elem (struct pdf_obj *array_obj, struct pdf_obj *val)
 {
-  struct pdf_array_elem *elem = pdf_calloc (sizeof (struct pdf_array_elem));
+  struct pdf_array_elem *elem = pdf_calloc (1, sizeof (struct pdf_array_elem));
 
   if (array_obj->type == PT_IND_REF)
     array_obj = pdf_deref_ind_obj (array_obj);
@@ -194,7 +203,7 @@ void pdf_add_array_elem (struct pdf_obj *array_obj, struct pdf_obj *val)
 
 struct pdf_obj *pdf_new_obj (pdf_obj_type type)
 {
-  struct pdf_obj *obj = pdf_calloc (sizeof (struct pdf_obj));
+  struct pdf_obj *obj = pdf_calloc (1, sizeof (struct pdf_obj));
   obj->type = type;
   return (obj);
 }
@@ -453,6 +462,65 @@ void pdf_stream_write_data (pdf_file_handle pdf_file,
 }
 
 
+void pdf_stream_flush_bits (pdf_file_handle pdf_file,
+			    struct pdf_obj *stream)
+{
+  struct pdf_stream *s = & stream->val.stream;
+
+  if (s->bit_idx)
+    {
+      /* zero remaining bits in last byte */
+      s->data [s->byte_idx] &= ~ ((1 << (8 - s->bit_idx)) - 1);
+      s->byte_idx++;
+      s->bit_idx = 0;
+    }
+  pdf_stream_write_data (pdf_file, stream, 
+			 (char *) & s->data [0],
+			 s->byte_idx);
+  s->byte_idx = 0;
+}
+
+
+static void pdf_stream_advance_byte (pdf_file_handle pdf_file,
+				     struct pdf_obj *stream)
+{
+  struct pdf_stream *s = & stream->val.stream;
+
+  s->byte_idx++;
+  s->bit_idx = 0;
+  if (s->byte_idx == STREAM_BUF_SIZE)
+    pdf_stream_flush_bits (pdf_file, stream);
+}
+
+
+void pdf_stream_write_bits (pdf_file_handle pdf_file,
+			    struct pdf_obj *stream,
+			    uint32_t count,
+			    uint32_t bits)
+{
+  struct pdf_stream *s = & stream->val.stream;
+
+  uint32_t b2;  /* how many bits will fit in byte in data buffer */
+  uint32_t c2;  /* how many bits to transfer on this iteration */
+  uint32_t d2;  /* bits to transfer on this iteration */
+
+  while (count)
+    {
+      b2 = 8 - s->bit_idx;
+      if (b2 >= count)
+	c2 = count;
+      else
+	c2 = b2;
+      d2 = bits >> (count - c2);
+      s->data [s->byte_idx] |= (d2 << (b2 + c2));
+      s->bit_idx += c2;
+      if (s->bit_idx > 7)
+	pdf_stream_advance_byte (pdf_file, stream);
+      count -= c2;
+    }
+}
+
+
 void pdf_stream_printf (pdf_file_handle pdf_file,
 			struct pdf_obj *stream,
 			char *fmt, ...)
diff --git a/pdf_prim.h b/pdf_prim.h
index 22bbbbd..e3fc073 100644
--- a/pdf_prim.h
+++ b/pdf_prim.h
@@ -4,7 +4,7 @@
  *      will be compressed using ITU-T T.6 (G4) fax encoding.
  *
  * PDF routines
- * $Id: pdf_prim.h,v 1.3 2003/02/21 01:25:47 eric Exp $
+ * $Id: pdf_prim.h,v 1.4 2003/02/21 02:49:11 eric Exp $
  * Copyright 2001, 2002, 2003 Eric Smith <eric@brouhaha.com>
  *
  * This program is free software; you can redistribute it and/or modify
@@ -95,8 +95,19 @@ struct pdf_obj *pdf_new_stream (pdf_file_handle pdf_file,
 				pdf_stream_write_callback callback,
 				void *app_data);
 
-/* The callback should call pdf_stream_write_data or pdf_stream_printf
-   to write the actual stream data. */
+/* The callback should call pdf_stream_write_bits(), pdf_stream_write_data(),
+   or pdf_stream_printf() to write the actual stream data.  If
+   pdf_stream_write_bits() is used, pdf_stream_flush_bits() should be
+   called after all the bits are written.  */
+
+void pdf_stream_write_bits (pdf_file_handle pdf_file,
+			    struct pdf_obj *stream,
+			    uint32_t count,
+			    uint32_t bits);
+
+void pdf_stream_flush_bits (pdf_file_handle pdf_file,
+			    struct pdf_obj *stream);
+
 void pdf_stream_write_data (pdf_file_handle pdf_file,
 			    struct pdf_obj *stream,
 			    char *data,
diff --git a/pdf_util.c b/pdf_util.c
index 47e683c..e0c30c0 100644
--- a/pdf_util.c
+++ b/pdf_util.c
@@ -4,7 +4,7 @@
  *      will be compressed using ITU-T T.6 (G4) fax encoding.
  *
  * PDF routines
- * $Id: pdf_util.c,v 1.3 2003/02/20 04:44:17 eric Exp $
+ * $Id: pdf_util.c,v 1.4 2003/02/21 02:49:11 eric Exp $
  * Copyright 2001, 2002, 2003 Eric Smith <eric@brouhaha.com>
  *
  * This program is free software; you can redistribute it and/or modify
@@ -48,9 +48,9 @@ void pdf_fatal (char *fmt, ...)
 }
 
 
-void *pdf_calloc (long int size)
+void *pdf_calloc (size_t nmemb, size_t size)
 {
-  void *m = calloc (1, size);
+  void *m = calloc (nmemb, size);
   if (! m)
     pdf_fatal ("failed to allocate memory\n");
   return (m);
@@ -60,7 +60,7 @@ void *pdf_calloc (long int size)
 char *pdf_strdup (char *s)
 {
   unsigned long len = strlen (s);
-  char *s2 = pdf_calloc (len + 1);
+  char *s2 = pdf_calloc (1, len + 1);
   strcpy (s2, s);
   return (s2);
 }
diff --git a/pdf_util.h b/pdf_util.h
index 2dcbc5e..971ae70 100644
--- a/pdf_util.h
+++ b/pdf_util.h
@@ -4,7 +4,7 @@
  *      will be compressed using ITU-T T.6 (G4) fax encoding.
  *
  * PDF routines
- * $Id: pdf_util.h,v 1.2 2003/02/20 04:44:17 eric Exp $
+ * $Id: pdf_util.h,v 1.3 2003/02/21 02:49:11 eric Exp $
  * Copyright 2001, 2002, 2003 Eric Smith <eric@brouhaha.com>
  *
  * This program is free software; you can redistribute it and/or modify
@@ -26,7 +26,7 @@
 
 void pdf_fatal (char *fmt, ...);
 
-void *pdf_calloc (long int size);
+void *pdf_calloc (size_t nmemb, size_t size);
 
 char *pdf_strdup (char *s);