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diff --git a/src/imageutils/croppedqimage.cpp b/src/imageutils/croppedqimage.cpp
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+++ b/src/imageutils/croppedqimage.cpp
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+/*
+
+ Copyright (C) 2005 Lubos Lunak <l.lunak@kde.org>
+
+ This program is free software; you can redistribute it and/or
+ modify it under the terms of the GNU General Public License
+ as published by the Free Software Foundation; either version 2
+ of the License, or (at your option) any later version.
+
+ This program is distributed in the hope that it will be useful,
+ but WITHOUT ANY WARRANTY; without even the implied warranty of
+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ GNU General Public License for more details.
+
+ You should have received a copy of the GNU General Public License
+ along with this program; if not, write to the Free Software
+ Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA  02111-1307, USA.
+
+*/
+
+#include "croppedqimage.h"
+
+namespace ImageUtils
+{
+
+// This class is used in ImageView::performPaint(). Just using QImage::copy( QRect )
+// takes a significant time with very large images. So instead of copying the image data
+// just create CroppedQImage which fakes a subimage by manipulating its scanline pointers.
+// That will of course break if something doesn't use scanlines but accesses the image
+// data directly, QImage::copy() being the most notable case. There are two ways
+// to handle that: 1) It is possible to manually call normalize() which will make
+// CroppedQImage copy the image data and own it, just like proper QImage. 2) CroppedQImage
+// has as a data member also QImage holding the original image. This ensures that all
+// the original image data are still available for the whole lifetime of CroppedQImage.
+
+CroppedQImage::CroppedQImage( const QImage& im, const QRect& rect )
+    : QImage( rect.size(), im.depth(), im.numColors(), im.bitOrder())
+    , orig( im )
+    {
+    if( im.isNull())
+        return;
+    memcpy( colorTable(), im.colorTable(), im.numColors() * sizeof( QRgb ));
+    setAlphaBuffer( im.hasAlphaBuffer());
+    setDotsPerMeterX( im.dotsPerMeterX());
+    setDotsPerMeterY( im.dotsPerMeterY());
+    //data->offset = im.offset();
+    // make scanlines point to right places in the original QImage
+    for( int i = 0;
+         i < height();
+         ++i )
+        jumpTable()[ i ] = im.scanLine( rect.y() + i ) + rect.x() * ( depth() / 8 );
+    }
+
+CroppedQImage& CroppedQImage::operator= ( const QImage& im )
+    {
+    QImage::operator=( im );
+    return *this;
+    }
+
+void CroppedQImage::normalize()
+    {
+    // is it a normal QImage with its own data?
+    uchar* firstdata = ( uchar* )( jumpTable() + height());
+    if( scanLine( 0 ) == firstdata )
+        return;
+    // copy the image data to our own data and make scanlines point properly there
+    for( int i = 0;
+         i < height();
+         ++i )
+        {
+        uchar* oldline = scanLine( i );
+        jumpTable()[ i ] = firstdata + i * bytesPerLine();
+        memcpy( scanLine( i ), oldline, bytesPerLine());
+        }
+    }
+
+} // namespace