Improve doc for garmin_gpi bitmap option.

diff --git a/xmldoc/formats/options/garmin_gpi-bitmap.xml b/xmldoc/formats/options/garmin_gpi-bitmap.xml
index 48317bb17398fa4f171e86ca13ed84e95235e946..a83f9cb364f3c38e87b64a94318ad87abaffac6b 100644 (file)
--- a/xmldoc/formats/options/garmin_gpi-bitmap.xml
+++ b/xmldoc/formats/options/garmin_gpi-bitmap.xml
@@ -2,6 +2,12 @@
    The bitmap (BMP) should be 24x24 (or smaller) and can be in
    RGB-colors (24- and 32-bit) or 8-bit indexed color format.
 </para>
+<para>
+  If you're starting from images in another format, you may need to
+  use another tool like Gimp or ImageMagick's convert to get the imaga
+  into oen of the above formats to avoid errors about "Unsupported color 
+  depth".
+</para>
 <para>
    A color value of 0xFF00FF (blue=255, green=0, red=255), 
    also called "Magenta", can be used for transparent areas.