Introducing optional env vars for ImageMagick

paperless.conf.example

@@ -32,7 +32,32 @@ PAPERLESS_PASSPHRASE="secret"
 # have a shared secret here.
 PAPERLESS_SHARED_SECRET=""
 
+#
+# The following values use sensible defaults for modern systems, but if you're
+# running Paperless on a low-resource machine (like a Rasberry Pi), modifying
+# some of these values may be necessary.
+#
+
 # By default, Paperless will attempt to use all available CPU cores to process
 # a document, but if you would like to limit that, you can set this value to
 # an integer:
 #PAPERLESS_OCR_THREADS=1
+
+# On smaller systems, or even in the case of Very Large Documents, the consumer
+# may explode, complaining about how it's "unable to extent pixel cache".  In
+# such cases, try setting this to a reasonably low value, like 32000000.  The
+# default is to use whatever is necessary to do everything without writing to
+# disk, and units are in megabytes.
+#
+# For more information on how to use this value, you should probably search
+# the web for "MAGICK_MEMORY_LIMIT".
+#PAPERLESS_CONVERT_MEMORY_LIMIT=0
+
+# Similar to the memory limit, if you've got a small system and your OS mounts
+# /tmp as tmpfs, you should set this to a path that's on a physical disk, like
+# /home/your_user/tmp or something.  ImageMagick will use this as scratch space
+# when crunching through very large documents.
+#
+# For more information on how to use this value, you should probably search
+# the web for "MAGICK_TMPDIR".
+#PAPERLESS_CONVERT_TMPDIR=/var/tmp/paperless