diff --git a/TODO b/TODO
index 7f1b494d..716a8682 100644
--- a/TODO
+++ b/TODO
@@ -1,3 +1,24 @@
+- large alpha PNGs seem to need huge amounts of ram to process
+
+john@bambam ~/pics $ vipsthumbnail wtc.png
+memory: high-water mark 31.37 MB
+john@bambam ~/pics $ vipsthumbnail wtc.png --linear
+memory: high-water mark 47.83 MB
+
+john@bambam ~/pics $ vipsthumbnail wtc_alpha.png 
+memory: high-water mark 41.85 MB
+john@bambam ~/pics $ vipsthumbnail wtc_alpha.png --linear
+memory: high-water mark 101.59 MB
+john@bambam ~/pics $ 
+
+  it seems to be the vips_colourspace() cast from sRGB to XYZ that's doing it?
+  how odd
+
+  maybe the thing that detaches and reattaches the alpha?
+
+- still don't get progress feedback in nip2 for a long png save, eg. make a
+  4-band wtc, save as png
+
 - support --strip for other writers
 
 - vipstumbnail is broken for the gamma trick png on eric brasseur's page