diff --git a/doc/python.tex b/doc/python.tex
index 2f0e4c56..bf230da4 100644
--- a/doc/python.tex
+++ b/doc/python.tex
@@ -479,7 +479,7 @@ from PyQt4.QtGui import QApplication, QMainWindow, QPainter, QImage
 class MitsubaView(QMainWindow):
     def __init__(self):
         super(MitsubaView, self).__init__()
-        self.setWindowTitle('Mitsuba/Qt demo')
+        self.setWindowTitle('Mitsuba/PyQt demo')
         self.initializeMitsuba()
         self.image = self.render(self.createScene())
         self.resize(self.image.width(), self.image.height())
@@ -598,7 +598,7 @@ class MitsubaRenderBuffer(RenderListener):
         """ Callback: a worker thread started rendering an image block.
             Draw a rectangle to highlight this """
         _ = self._get_film_ensure_initialized(job)
-        self.bitmap.drawRect(wu.getOffset(), wu.getSize(), Spectrum(0.8))
+        self.bitmap.drawWorkUnit(wu.getOffset(), wu.getSize(), thr)
         self._potentially_send_update()
 
     def workEndEvent(self, job, wr):
@@ -710,7 +710,7 @@ class MitsubaDemo(QMainWindow):
         status.setContentsMargins(0,0,5,0)
         status.addPermanentWidget(progress)
         status.setSizeGripEnabled(False)
-        self.setWindowTitle('Mitsuba/Qt demo')
+        self.setWindowTitle('Mitsuba/PyQt demo')
         self.setCentralWidget(self.rwidget)
 
         # Hide the scroll bar once the rendering is done
diff --git a/include/mitsuba/core/bitmap.h b/include/mitsuba/core/bitmap.h
index 6d8ce6c3..a0380fe1 100644
--- a/include/mitsuba/core/bitmap.h
+++ b/include/mitsuba/core/bitmap.h
@@ -446,6 +446,12 @@ public:
 	/// Draw a filled rectangle with the specified position and size
 	void fillRect(Point2i offset, Vector2i size, const Spectrum &value);
 
+	/**
+	 * \brief Convenience function to visually indicate that a thread is
+	 * working on a certain part of an image
+	 */
+	void drawWorkUnit(const Point2i &offset, const Vector2i &size, int worker);
+
 	/// Bitmap equality operator (useful for unit-tests etc.)
 	bool operator==(const Bitmap &bitmap) const;
 
diff --git a/src/libcore/bitmap.cpp b/src/libcore/bitmap.cpp
index b95f936c..bb88d531 100644
--- a/src/libcore/bitmap.cpp
+++ b/src/libcore/bitmap.cpp
@@ -3278,6 +3278,56 @@ ref<Bitmap> Bitmap::expand() {
 	return output;
 }
 
+void Bitmap::drawWorkUnit(const Point2i &offset, const Vector2i &size, int worker) {
+	int ox = offset.x, oy = offset.y,
+		ex = ox + size.x, ey = oy + size.y;
+	if (size.x < 3 || size.y < 3)
+		return;
+
+	const float *color = NULL;
+
+	/* Use desaturated colors to highlight the worker
+	   responsible for rendering the current image */
+	const float white[]     = { 1.0f, 1.0f, 1.0f };
+	const float red[]       = { 1.0f, 0.3f, 0.3f };
+	const float green[]     = { 0.3f, 1.0f, 0.3f };
+	const float blue[]      = { 0.3f, 0.3f, 1.0f };
+	const float gray[]      = { 0.5f, 0.5f, 0.5f };
+	const float yellow[]    = { 1.0f, 1.0f, 0.0f };
+	const float magenta[]   = { 1.0f, 0.3f, 1.0f };
+	const float turquoise[] = { 0.3f, 1.0f, 1.0f };
+
+	switch (worker % 8) {
+		case 1: color = green; break;
+		case 2: color = yellow; break;
+		case 3: color = blue; break;
+		case 4: color = gray; break;
+		case 5: color = red; break;
+		case 6: color = magenta; break;
+		case 7: color = turquoise; break;
+		case 0:
+		default:
+			color = white;
+			break;
+	}
+
+	float scale = .7f * (color[0] * 0.212671f + color[1] * 0.715160f + color[2] * 0.072169f);
+
+	Spectrum spec;
+	spec.fromLinearRGB(color[0]*scale,
+		color[1]*scale,
+		color[2]*scale);
+
+	drawHLine(oy, ox, ox + 3, spec);
+	drawHLine(oy, ex - 4, ex - 1, spec);
+	drawHLine(ey - 1, ox, ox + 3, spec);
+	drawHLine(ey - 1, ex - 4, ex - 1, spec);
+	drawVLine(ox, oy, oy + 3, spec);
+	drawVLine(ex - 1, oy, oy + 3, spec);
+	drawVLine(ex - 1, ey - 4, ey - 1, spec);
+	drawVLine(ox, ey - 4, ey - 1, spec);
+}
+
 std::ostream &operator<<(std::ostream &os, const Bitmap::EPixelFormat &value) {
 	switch (value) {
 		case Bitmap::ELuminance: os << "luminance"; break;
diff --git a/src/libpython/core.cpp b/src/libpython/core.cpp
index 01e18ddc..dad3a90d 100644
--- a/src/libpython/core.cpp
+++ b/src/libpython/core.cpp
@@ -1249,6 +1249,7 @@ void export_core() {
 		.def("getMetadata", get_metadata, BP_RETURN_VALUE)
 		.def("drawRect", &Bitmap::drawRect)
 		.def("fillRect", &Bitmap::fillRect)
+		.def("drawWorkUnit", &Bitmap::drawWorkUnit)
 		.def("convert", &bitmap_convert_1, BP_RETURN_VALUE)
 		.def("convert", &bitmap_convert_2, BP_RETURN_VALUE)
 		.def("convert", &bitmap_convert_3, BP_RETURN_VALUE)