an assertion fails when Jasper is fed certain JPEG-2000 files with an alpha channel. See: http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=469786

src_libjasper_jpc_jpc_dec.c.patch

--- a/src/libjasper/jpc/jpc_dec.c.orig	2015-12-27 21:58:46.000000000 +0100
+++ a/src/libjasper/jpc/jpc_dec.c	2015-12-27 22:01:41.000000000 +0100
@@ -1069,12 +1069,18 @@
 	/* Apply an inverse intercomponent transform if necessary. */
 	switch (tile->cp->mctid) {
 	case JPC_MCT_RCT:
-		assert(dec->numcomps == 3);
+                if (dec->numcomps != 3 && dec->numcomps != 4) {
+                        jas_eprintf("bad number of components (%d)\n", dec->numcomps);
+                        return -1;
+                }
 		jpc_irct(tile->tcomps[0].data, tile->tcomps[1].data,
 		  tile->tcomps[2].data);
 		break;
 	case JPC_MCT_ICT:
-		assert(dec->numcomps == 3);
+                if (dec->numcomps != 3 && dec->numcomps != 4) {
+                        jas_eprintf("bad number of components (%d)\n", dec->numcomps);
+                        return -1;
+                }
 		jpc_iict(tile->tcomps[0].data, tile->tcomps[1].data,
 		  tile->tcomps[2].data);
 		break;