diff --git a/libpng-manual.txt b/libpng-manual.txt
index 2f5c589..e306978 100644
--- a/libpng-manual.txt
+++ b/libpng-manual.txt
@@ -1,6 +1,6 @@
 libpng-manual.txt - A description on how to use and modify libpng
 
- libpng version 1.6.33rc02 - September 20, 2017
+ libpng version 1.6.33rc02 - September 23, 2017
  Updated and distributed by Glenn Randers-Pehrson
  <glennrp at users.sourceforge.net>
  Copyright (c) 1998-2017 Glenn Randers-Pehrson
@@ -11,7 +11,7 @@
 
  Based on:
 
- libpng versions 0.97, January 1998, through 1.6.33rc02 - September 20, 2017
+ libpng versions 0.97, January 1998, through 1.6.33rc02 - September 23, 2017
  Updated and distributed by Glenn Randers-Pehrson
  Copyright (c) 1998-2017 Glenn Randers-Pehrson
 
@@ -986,8 +986,17 @@
 
     png_set_alpha_mode(pp, PNG_ALPHA_PNG, PNG_DEFAULT_sRGB);
 
-This is the default libpng handling of the alpha channel - it is not
-pre-multiplied into the color components.  In addition the call states
+Choices for the alpha_mode are
+
+    PNG_ALPHA_PNG           0 /* according to the PNG standard */
+    PNG_ALPHA_STANDARD      1 /* according to Porter/Duff */
+    PNG_ALPHA_ASSOCIATED    1 /* as above; this is the normal practice */
+    PNG_ALPHA_PREMULTIPLIED 1 /* as above */
+    PNG_ALPHA_OPTIMIZED     2 /* 'PNG' for opaque pixels, else 'STANDARD' */
+    PNG_ALPHA_BROKEN        3 /* the alpha channel is gamma encoded */
+
+PNG_ALPHA_PNG is the default libpng handling of the alpha channel. It is not
+pre-multiplied into the color components. In addition the call states
 that the output is for a sRGB system and causes all PNG files without gAMA
 chunks to be assumed to be encoded using sRGB.
 
@@ -1002,7 +1011,7 @@
 This is the classic Jim Blinn approach and will work in academic
 environments where everything is done by the book.  It has the shortcoming
 of assuming that input PNG data with no gamma information is linear - this
-is unlikely to be correct unless the PNG files where generated locally.
+is unlikely to be correct unless the PNG files were generated locally.
 Most of the time the output precision will be so low as to show
 significant banding in dark areas of the image.
 
diff --git a/libpng.3 b/libpng.3
index 0b991b9..8ee0d4b 100644
--- a/libpng.3
+++ b/libpng.3
@@ -1,4 +1,4 @@
-.TH LIBPNG 3 "September 20, 2017"
+.TH LIBPNG 3 "September 23, 2017"
 .SH NAME
 libpng \- Portable Network Graphics (PNG) Reference Library 1.6.33rc02
 .SH SYNOPSIS
@@ -518,7 +518,7 @@
 .SH LIBPNG.TXT
 libpng-manual.txt - A description on how to use and modify libpng
 
- libpng version 1.6.33rc02 - September 20, 2017
+ libpng version 1.6.33rc02 - September 23, 2017
  Updated and distributed by Glenn Randers-Pehrson
  <glennrp at users.sourceforge.net>
  Copyright (c) 1998-2017 Glenn Randers-Pehrson
@@ -529,7 +529,7 @@
 
  Based on:
 
- libpng versions 0.97, January 1998, through 1.6.33rc02 - September 20, 2017
+ libpng versions 0.97, January 1998, through 1.6.33rc02 - September 23, 2017
  Updated and distributed by Glenn Randers-Pehrson
  Copyright (c) 1998-2017 Glenn Randers-Pehrson
 
@@ -1504,8 +1504,17 @@
 
     png_set_alpha_mode(pp, PNG_ALPHA_PNG, PNG_DEFAULT_sRGB);
 
-This is the default libpng handling of the alpha channel - it is not
-pre-multiplied into the color components.  In addition the call states
+Choices for the alpha_mode are
+
+    PNG_ALPHA_PNG           0 /* according to the PNG standard */
+    PNG_ALPHA_STANDARD      1 /* according to Porter/Duff */
+    PNG_ALPHA_ASSOCIATED    1 /* as above; this is the normal practice */
+    PNG_ALPHA_PREMULTIPLIED 1 /* as above */
+    PNG_ALPHA_OPTIMIZED     2 /* 'PNG' for opaque pixels, else 'STANDARD' */
+    PNG_ALPHA_BROKEN        3 /* the alpha channel is gamma encoded */
+
+PNG_ALPHA_PNG is the default libpng handling of the alpha channel. It is not
+pre-multiplied into the color components. In addition the call states
 that the output is for a sRGB system and causes all PNG files without gAMA
 chunks to be assumed to be encoded using sRGB.
 
@@ -1520,7 +1529,7 @@
 This is the classic Jim Blinn approach and will work in academic
 environments where everything is done by the book.  It has the shortcoming
 of assuming that input PNG data with no gamma information is linear - this
-is unlikely to be correct unless the PNG files where generated locally.
+is unlikely to be correct unless the PNG files were generated locally.
 Most of the time the output precision will be so low as to show
 significant banding in dark areas of the image.
 
@@ -6081,7 +6090,7 @@
 
 Thanks to Frank J. T. Wojcik for helping with the documentation.
 
-Libpng version 1.6.33rc02 - September 20, 2017:
+Libpng version 1.6.33rc02 - September 23, 2017:
 Initially created in 1995 by Guy Eric Schalnat, then of Group 42, Inc.
 Currently maintained by Glenn Randers-Pehrson (glennrp at users.sourceforge.net).
 
@@ -6106,7 +6115,7 @@
 
 This code is released under the libpng license.
 
-libpng versions 1.0.7, July 1, 2000 through 1.6.33rc02, September 20, 2017 are
+libpng versions 1.0.7, July 1, 2000 through 1.6.33rc02, September 23, 2017 are
 Copyright (c) 2000-2002, 2004, 2006-2017 Glenn Randers-Pehrson, are
 derived from libpng-1.0.6, and are distributed according to the same
 disclaimer and license as libpng-1.0.6 with the following individuals
@@ -6234,7 +6243,7 @@
 
 Glenn Randers-Pehrson
 glennrp at users.sourceforge.net
-September 20, 2017
+September 23, 2017
 
 .\" end of man page