miscellaneous update

git-svn-id: http://svn.code.sf.net/p/netpbm/code/userguide@3921 9d0c8265-081b-0410-96cb-a4ca84ce46f8

1 files changed, 16 insertions, 2 deletions

diff --git a/pnmcrop.html b/pnmcrop.html
index e2282d1f..b2f6968a 100644
--- a/pnmcrop.html
+++ b/pnmcrop.html
@@ -258,7 +258,8 @@ fails if there is no apparent background color in the original image
   <dd>program fails, with explanatory message (default)
 
   <dt>pass
-  <dd>no modification to image
+    <dd>Output image is the same as the input image.
+      <b>-margin</b> has no effect.
 
   <dt>minimize
     <dd>output is a single row, column, or pixel (of the background color).
@@ -267,12 +268,25 @@ fails if there is no apparent background color in the original image
       original width.  If you crop only horizontally, it is a single column,
       of the original height.
 
-      The background can be more than one color when you specify
+      <p>This is a somewhat incongruous result; the mathematically consistent
+        result of cropping the background from an image that is entirely
+        background would be an image with no pixels at all.  But such a thing
+        does not exist in the Netpbm formats (and you probably wouldn't want
+        it anyway, because whoever processes this output may not tolerate
+        that).
+
+      <p>The background can be more than one color when you specify
       <b>-closeness</b>, so it matters which row, column, or pixel remains.
       If you crop on the top and not bottom, it is the last row that remains.
       If you crop on both the top and bottom, it is the middle row that
       remains.  The other cases follow similarly.
 
+      <p>If you specify a margin (<b>-margin</b>), the output image consists
+        entirely of the margins; there is no single row, column, or pixel
+        between the margins.  So with <b>-margin</b>, the incongruity
+        mentioned above does not exist.  But before Netpbm 10.92 (September
+        2020), <b>-margin</b> was ignored with <b>-blank-image=minimize</b>.
+
   <dt>maxcrop
     <dd>This odd function selects a hypothetical cropping which is not even
       possible, and therefore is valid only with <b>-reportfull</b> or