Apply "Added paragraph about image polarity as discussed on sane-devel"

conf.py

@@ -53,7 +53,7 @@ numfig_format = {
     'section': '%s'
 }
 
-today_fmt = 'July 31, 2000'
+today_fmt = 'October 17, 2000'
 
 highlight_language = 'c'
 

environment.rst

@@ -230,3 +230,9 @@ This version of the SANE standard supports the following frame types:
     :macro:`SANE_FRAME_GREEN`, and
     :macro:`SANE_FRAME_BLUE`. The order in which the
     frames are transmitted chosen by the backend.
+
+In frames of type :macro:`SANE_FRAME_GRAY`, when the bit depth is 1 there are
+only two sample values possible, 1 represents minimum intensity
+(black) and 0 represents maximum intensity (white).  For all other bit
+depth and frame type combinations, a sample value of 0 represents
+minimum intensity and larger values represent increasing intensity.