bug?

TODO

@@ -1,3 +1,25 @@
+- try making a 1000 x 500 x 500 float image on disc, then
+
+	https://gist.github.com/jcupitt/93e7248bf9eddc34c4cb
+
+  see:
+
+	$ time ./slice.py ~/pics/1000x500x500.v 
+	vips warning: VipsImage: /Users/john/pics/1000x500x500.v is longer than
+	expected
+	Traceback (most recent call last):
+	File "./slice.py", line 26, in <module> row.falsecolour().write_to_file("row.v")
+	File "/usr/local/lib/python2.7/site-packages/gi/overrides/Vips.py", line 570, in write_to_file _call_base(saver, [filename], kwargs, self, option_string)
+	File "/usr/local/lib/python2.7/site-packages/gi/overrides/Vips.py", line 338, in _call_base
+	raise Error('Error calling operator %s.' % name)
+	gi.overrides.Vips.Error: Error calling operator
+	VipsForeignSaveVips.
+	VipsRegion: images do not match in pixel size
+	VipsRegion: valid clipped to nothing
+
+  caching is breaking with copy() stuff, somehow?
+
+
 - are the mosaic functions calling vips_fastcor()? it must be very slow
 
   add vips_fastcor_direct()