From 813fc816238dda378d62781b80f25045e83c6b14 Mon Sep 17 00:00:00 2001
From: Kovid Goyal <kovid@kovidgoyal.net>
Date: Fri, 6 May 2016 18:28:21 +0530
Subject: [PATCH] ...

---
 src/calibre/utils/imageops/imageops.cpp | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/src/calibre/utils/imageops/imageops.cpp b/src/calibre/utils/imageops/imageops.cpp
index f772f14c3a..e015e9d131 100644
--- a/src/calibre/utils/imageops/imageops.cpp
+++ b/src/calibre/utils/imageops/imageops.cpp
@@ -606,6 +606,7 @@ void overlay(const QImage &image, QImage &canvas, unsigned int left, unsigned in
             img = img.convertToFormat(QImage::Format_ARGB32_Premultiplied);
             if (img.isNull()) throw std::bad_alloc();
         }
+        Py_BEGIN_ALLOW_THREADS;
         for (r = 0; r < height; r++) {
             src = reinterpret_cast<const QRgb*>(img.constScanLine(r));
             dest = reinterpret_cast<QRgb*>(canvas.scanLine(r + top));
@@ -620,13 +621,16 @@ void overlay(const QImage &image, QImage &canvas, unsigned int left, unsigned in
                 else if (s != 0) dest[left+c] = s + BYTE_MUL(dest[left+c], qAlpha(~s));
             }
         }
+        Py_END_ALLOW_THREADS;
     } else {
         ENSURE32(img);
+        Py_BEGIN_ALLOW_THREADS;
         for (r = 0; r < bottom; r++) {
             src = reinterpret_cast<const QRgb*>(img.constScanLine(r));
             dest = reinterpret_cast<QRgb*>(canvas.scanLine(r + top));
             memcpy(dest + left, src, (right - left) * sizeof(QRgb));
         }
+        Py_END_ALLOW_THREADS;
     }
 
 } // }}}