ImageMagick warnings cause binarization segfaults

[bertsky]

When ImageMagick outputs warnings about bad image tags, OLENA's binarization programs all segfault like so:

ocrd-olena-binarize -I OCR-D-IMG -O OCR-D-IMG-BIN -p param-binarize-sauvola-ms-split.json
terminate called after throwing an instance of 'Magick::WarningCoder'
  what():  sauvola_ms_split: ASCII value for tag "Artist" does not end in null byte. `TIFFFetchNormalTag' @ warning/tiff.c/TIFFWarnings/912
Aborted (core dumped)

This most likely needs to be fixed upstream in OLENA.

[bertsky]

I backtraced with the debugger. Now I have a sketch of a solution. We need to catch ImageMagick's exceptions with a patch for olena:

When scribo calls milena's mln::io::magick::load, this uses Magick::Image::read without any try/catch clause whatsoever. Thankfully, the comment already concedes that:

	// FIXME: Handle Magick++'s exceptions (see either
	// ImageMagick++'s or GraphicsMagick++'s documentation).
	Magick::Image magick_ima(filename);
	magick_ima.read(filename);

So using Magick's documentation I made the following patch:

--- olena-2.1/milena/mln/io/magick/load.hh	2014-07-01 17:31:28.911721811 +0200
+++ olena-2.1/milena/mln/io/magick/load.hh	2019-08-16 00:05:22.921562018 +0200
@@ -153,7 +153,24 @@
 	// FIXME: Handle Magick++'s exceptions (see either
 	// ImageMagick++'s or GraphicsMagick++'s documentation).
 	Magick::Image magick_ima(filename);
-	magick_ima.read(filename);
+    try {
+      magick_ima.read(filename);
+    }
+    catch( Magick::WarningCoder &warning ) {
+      // Process coder warning while loading file (e.g. TIFF warning)
+      // Maybe the user will be interested in these warnings (or not).
+      // If a warning is produced while loading an image, the image
+      // can normally still be used (but not if the warning was about
+      // something important!)
+      std::cerr << "warning: magick read: " << warning.what() << std::endl;
+    } catch( Magick::Warning &warning ) {
+      // Handle any other Magick++ warning.
+      std::cerr << "warning: magick read: " << warning.what() << std::endl;
+    } catch( Magick::ErrorFileOpen &error ) {
+      // Process Magick++ file open error
+      std::cerr << "error: magick read: " << error.what() << std::endl;
+      abort();
+    }
 	magick_ima.type(Magick::TrueColorType);
 	int nrows = magick_ima.rows();
 	int ncols = magick_ima.columns();

This works – it turns the above abort into the following warning and resumes operation normally:

warning: magick read: wolf: Incorrect value for "Photoshop"; tag ignored. `TIFFFetchNormalTag' @ warning/tiff.c/TIFFWarnings/912

Now, how do we proceed? Package our patch into our wrapper, or hope for upstream approval? @wrznr @kba

[bertsky]

(And if the former – in #5 or as a new PR?)

[bertsky]

created #6