Use the nominal theme's icon size for displaying the icon in an info inset.

src/insets/InsetInfo.cpp

@@ -31,6 +31,7 @@
 
 #include "frontends/Application.h"
 
+#include "support/convert.h"
 #include "support/debug.h"
 #include "support/docstream.h"
 #include "support/docstring_list.h"
@@ -410,6 +411,8 @@ void InsetInfo::updateInfo()
 		InsetGraphics * inset = new InsetGraphics(buffer_);
 		InsetGraphicsParams igp;
 		igp.filename = file;
+		igp.lyxscale = iconScaleFactor(file);
+		igp.scale = convert<string>(igp.lyxscale);
 		inset->setParams(igp);
 		clear();
 		Font const f(inherit_font, buffer().params().language);

src/support/filetools.cpp

@@ -37,6 +37,7 @@
 #include "support/qstring_helpers.h"
 
 #include <QDir>
+#include <QImage>
 #include <QTemporaryFile>
 
 #include "support/lassert.h"
@@ -407,6 +408,24 @@ FileName const imageLibFileSearch(string & dir, string const & name,
 }
 
 
+int iconScaleFactor(FileName const & image)
+{
+	int imgsize = QImage(toqstr(image.absFileName())).height();
+	if (imgsize <= 0)
+		return 100;
+
+	// default icon size
+	int iconsize = 20;
+
+	string dir = "images";
+	FileName const fn = imageLibFileSearch(dir, "iconsize.png");
+	if (!fn.empty())
+		iconsize = QImage(toqstr(fn.absFileName())).height();
+
+	return (100 * iconsize + imgsize / 2)/imgsize;
+}
+
+
 string const commandPrep(string const & command_in)
 {
 	static string const token_scriptpath = "$$s/";

src/support/filetools.h

@@ -115,6 +115,11 @@ imageLibFileSearch(std::string & dir, std::string const & name,
 		   std::string const & ext = std::string(),
 		   search_mode mode = must_exist);
 
+/** Returns the percentage factor by which an image has to be
+    scaled for matching the (theme dependent) nominal icon size
+  */
+int iconScaleFactor(FileName const & image);
+
 /// How to quote a filename
 enum quote_style {
 	/** Quote for the (OS dependant) shell. This is needed for command