Made some TIFF reading adjustments.

Read a few TIFF tags that assist with having a similar TIFF file when saving the image again, instead of (by default) always saving as a 24-bit RGB image. Also, in accordance with libtiff, allow reading X and Y resolution values even if the resolution unit tag is not set.

Applied (modified) patch by scottb. Closes #13015.


git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@67264 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/common/imagtiff.cpp

@@ -402,42 +402,78 @@ bool wxTIFFHandler::LoadFile( wxImage *image, wxInputStream& stream, bool verbos
             alpha -= 2*w;
     }
 
-    // set the image resolution if it's available
+
-    uint16 tiffRes;
+    uint16 spp, bpp, compression;
-    if ( TIFFGetField(tif, TIFFTAG_RESOLUTIONUNIT, &tiffRes) )
+    /*
+    Read some baseline TIFF tags which helps when re-saving a TIFF
+    to be similar to the original image.
+    */
+    if ( TIFFGetFieldDefaulted(tif, TIFFTAG_SAMPLESPERPIXEL, &spp) )
     {
-        wxImageResolution res;
+        image->SetOption(wxIMAGE_OPTION_SAMPLESPERPIXEL, spp);
-        switch ( tiffRes )
+    }
+
+    if ( TIFFGetFieldDefaulted(tif, TIFFTAG_BITSPERSAMPLE, &bpp) )
+    {
+        image->SetOption(wxIMAGE_OPTION_BITSPERSAMPLE, bpp);
+    }
+
+    if ( TIFFGetFieldDefaulted(tif, TIFFTAG_COMPRESSION, &compression) )
+    {
+        image->SetOption(wxIMAGE_OPTION_COMPRESSION, compression);
+    }
+
+    // Set the resolution unit.
+    wxImageResolution resUnit = wxIMAGE_RESOLUTION_NONE;
+    uint16 tiffRes;
+    if ( TIFFGetFieldDefaulted(tif, TIFFTAG_RESOLUTIONUNIT, &tiffRes) )
+    {
+        switch (tiffRes)
         {
             default:
                 wxLogWarning(_("Unknown TIFF resolution unit %d ignored"),
-                             tiffRes);
+                    tiffRes);
                 // fall through
 
             case RESUNIT_NONE:
-                res = wxIMAGE_RESOLUTION_NONE;
+                resUnit = wxIMAGE_RESOLUTION_NONE;
                 break;
 
             case RESUNIT_INCH:
-                res = wxIMAGE_RESOLUTION_INCHES;
+                resUnit = wxIMAGE_RESOLUTION_INCHES;
                 break;
 
             case RESUNIT_CENTIMETER:
-                res = wxIMAGE_RESOLUTION_CM;
+                resUnit = wxIMAGE_RESOLUTION_CM;
                 break;
         }
-
-        if ( res != wxIMAGE_RESOLUTION_NONE )
-        {
-            float xres, yres;
-            if ( TIFFGetField(tif, TIFFTAG_XRESOLUTION, &xres) )
-                image->SetOption(wxIMAGE_OPTION_RESOLUTIONX, wxRound(xres));
-
-            if ( TIFFGetField(tif, TIFFTAG_YRESOLUTION, &yres) )
-                image->SetOption(wxIMAGE_OPTION_RESOLUTIONY, wxRound(yres));
-        }
     }
 
+    image->SetOption(wxIMAGE_OPTION_RESOLUTIONUNIT, resUnit);
+
+    /*
+    Set the image resolution if it's available. Resolution tag is not
+    dependant on RESOLUTIONUNIT != RESUNIT_NONE (according to TIFF spec).
+    */
+    float resX, resY;
+
+    if ( TIFFGetField(tif, TIFFTAG_XRESOLUTION, &resX) )
+    {
+        /*
+        Use a string value to not lose precision.
+        rounding to int as cm and then converting to inch may
+        result in whole integer rounding error, eg. 201 instead of 200 dpi.
+        If an app wants an int, GetOptionInt will convert and round down.
+        */
+        image->SetOption(wxIMAGE_OPTION_RESOLUTIONX,
+            wxString::FromCDouble((double) resX));
+    }
+
+    if ( TIFFGetField(tif, TIFFTAG_YRESOLUTION, &resY) )
+    {
+        image->SetOption(wxIMAGE_OPTION_RESOLUTIONY,
+            wxString::FromCDouble((double) resY));
+    }
 
     _TIFFfree( raster );