From 1de94d39e2c54a0d348363b5d857f0bfe5ad2ad9 Mon Sep 17 00:00:00 2001
From: Kovid Goyal <kovid@kovidgoyal.net>
Date: Sat, 18 May 2019 15:41:38 +0530
Subject: [PATCH] Report detected image type in exception

---
 src/calibre/utils/img.py | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/src/calibre/utils/img.py b/src/calibre/utils/img.py
index 8c8083cabb..af9a33b24a 100644
--- a/src/calibre/utils/img.py
+++ b/src/calibre/utils/img.py
@@ -82,9 +82,10 @@ def image_from_data(data):
         return data
     i = QImage()
     if not i.loadFromData(data):
-        if what(None, data) == 'jxr':
+        q = what(None, data)
+        if q == 'jxr':
             return load_jxr_data(data)
-        raise NotImage('Not a valid image')
+        raise NotImage('Not a valid image (detected type: {})'.format(q))
     return i