[Digikam-devel] [Bug 148400] Problem loading 16bit Grayscale TIFF image [testcase]

[Maximilian Schultz]

------- You are receiving this mail because: -------
You are the assignee for the bug, or are watching the assignee.
         
http://bugs.kde.org/show_bug.cgi?id=148400         




------- Additional Comments From mgschultz gmx net  2008-05-28 03:12 -------
I think, I have found (and solved) the bug. According to tiffloader.cpp digikam only knows about TIFF with three or four samples per pixel. A greyscale image, as one can confirm easily using "identify -verbose" has only one sample per pixel. The word in the strip provided by libtiff has thus to be written in all three channels.
I've written a small patch providing the additional routines. But beware, the PPC for BigEndian is probably still faulty, as I am not experienced enough to deal with Big-/LittleEndian properly.

After applying the patch, thumbnails and previews are generated properly. Also Showfoto loads and displays the pictures as it ought to. The only problem I encountered so far is that the image viewer for the previews cannot rotate the images...Maybe someone knows more about this than I.

But get to the facts, here is the patch as produced by svn diff > my.patch

Max, who know can also use digikam for the 16bit greyscale scans of his slides.

---------------------------------------------------------------------------
Index: tiffloader.cpp
===================================================================
--- tiffloader.cpp      (revision 813472)
+++ tiffloader.cpp      (working copy)
 @ -262,9 +262,10  @
             ushort *dataPtr  = (ushort*)(data + offset);
             ushort *p;

-            // tiff data is read as BGR or ABGR

-            if (samples_per_pixel == 3)
+            // tiff data is read as BGR or ABGR or Greyscale
+
+            if (samples_per_pixel == 3) // BGR
             {
                 for (int i=0; i < bytesRead/6; i++)
                 {
 @ -291,8 +292,35  @

                 offset += bytesRead/6 * 8;
             }
-            else
-            {
+           else
+               if (samples_per_pixel == 1) // Greyscale pictures only have _one_ sample per pixel
+               {
+               for (int i=0; i < bytesRead/2; i++)  // We have to read two bytes for one pixel
+                {
+                    p = dataPtr;
+
+                    // See B.K.O #148037 : take a care about byte order with Motorola computers.
+                   // I don't touch this... In this context it might produce nonsense.
+                    if (QImage::systemByteOrder() == QImage::BigEndian)     // PPC
+                    {
+                        p[3] = 0xFFFF;
+                        p[0] = *stripPtr;
+                        p[1] = *stripPtr;
+                        p[2] = *stripPtr++;
+                    }
+                    else
+                    {
+                        p[0] = *stripPtr;      // RGB have to be set to the _same_ value
+                        p[1] = *stripPtr;
+                        p[2] = *stripPtr++;
+                        p[3] = 0xFFFF;         // set alpha to 100%
+                    }
+                    dataPtr += 4;
+               }
+                offset += bytesRead*4;         // The _byte_offset in the data array is, of course, four times bytesRead
+               }
+            else // ABGR
+           {
                 for (int i=0; i < bytesRead/8; i++)
                 {
                     p = dataPtr;
 @ -319,7 +347,6  @
                 offset += bytesRead;
             }
         }
-
         delete [] strip;
     }
     else       // Non 16 bits images ==> get it on BGRA 8 bits.

---------------------------------------------------------------------------