diff --git a/PlotCanvas.py b/PlotCanvas.py
index 1634c996..a41e3715 100644
--- a/PlotCanvas.py
+++ b/PlotCanvas.py
@@ -22,6 +22,21 @@ log = logging.getLogger('base')
 
 
 class CanvasCache(QtCore.QObject):
+    """
+
+    Case story #1:
+
+    1) No objects in the project.
+    2) Object is created (new_object() emits object_created(obj)).
+       on_object_created() adds (i) object to collection and emits
+       (ii) new_object_available() then calls (iii) object.plot()
+    3) object.plot() creates axes if necessary on
+       app.collection.figure. Then plots on it.
+    4) Plots on a cache-size canvas (in background).
+    5) Plot completes. Bitmap is generated.
+    6) Visible canvas is painted.
+
+    """
 
     # Signals:
     # A bitmap is ready to be displayed.
diff --git a/tests/canvas/performance.py b/tests/canvas/performance.py
new file mode 100644
index 00000000..9478bcbf
--- /dev/null
+++ b/tests/canvas/performance.py
@@ -0,0 +1,95 @@
+from __future__ import division
+import matplotlib
+matplotlib.use('Agg')
+import matplotlib.pyplot as plt
+import numpy as np
+import cStringIO
+from matplotlib.backends.backend_agg import FigureCanvasAgg
+from matplotlib.backends.backend_qt4agg import FigureCanvasQTAgg
+from matplotlib.figure import Figure
+import cProfile
+import sys
+
+
+def gen_data():
+    N = 100000
+    x = np.random.rand(N) * 10
+    y = np.random.rand(N) * 10
+    colors = np.random.rand(N)
+    area = np.pi * (15 * np.random.rand(N))**2  # 0 to 15 point radiuses
+    data = x, y, area, colors
+    return data
+
+
+# @profile
+def large_plot(data):
+    x, y, area, colors = data
+
+    fig = Figure(figsize=(10, 10), dpi=80)
+    axes = fig.add_axes([0.0, 0.0, 1.0, 1.0], alpha=1.0)
+    axes.set_frame_on(False)
+    axes.set_xticks([])
+    axes.set_yticks([])
+    # axes.set_xlim(0, 10)
+    # axes.set_ylim(0, 10)
+
+    axes.scatter(x, y, s=area, c=colors, alpha=0.5)
+
+    axes.set_xlim(0, 10)
+    axes.set_ylim(0, 10)
+
+    canvas = FigureCanvasAgg(fig)
+    canvas.draw()
+    # canvas = FigureCanvasQTAgg(fig)
+    # buf = canvas.tostring_rgb()
+    buf = fig.canvas.tostring_rgb()
+
+    ncols, nrows = fig.canvas.get_width_height()
+    img = np.fromstring(buf, dtype=np.uint8).reshape(nrows, ncols, 3)
+
+    return img
+
+
+def small_plot(data):
+    x, y, area, colors = data
+
+    fig = Figure(figsize=(3, 3), dpi=80)
+    axes = fig.add_axes([0.0, 0.0, 1.0, 1.0], alpha=1.0)
+    axes.set_frame_on(False)
+    axes.set_xticks([])
+    axes.set_yticks([])
+    # axes.set_xlim(5, 6)
+    # axes.set_ylim(5, 6)
+
+    axes.scatter(x, y, s=area, c=colors, alpha=0.5)
+
+    axes.set_xlim(4, 7)
+    axes.set_ylim(4, 7)
+
+    canvas = FigureCanvasAgg(fig)
+    canvas.draw()
+    # canvas = FigureCanvasQTAgg(fig)
+    # buf = canvas.tostring_rgb()
+    buf = fig.canvas.tostring_rgb()
+
+    ncols, nrows = fig.canvas.get_width_height()
+    img = np.fromstring(buf, dtype=np.uint8).reshape(nrows, ncols, 3)
+
+    return img
+
+def doit():
+    d = gen_data()
+    img = large_plot(d)
+    return img
+
+
+if __name__ == "__main__":
+
+    d = gen_data()
+
+    if sys.argv[1] == 'large':
+        cProfile.runctx('large_plot(d)', None, locals())
+    else:
+        cProfile.runctx('small_plot(d)', None, locals())
+
+
diff --git a/tests/canvas/prof.sh b/tests/canvas/prof.sh
new file mode 100755
index 00000000..b9075848
--- /dev/null
+++ b/tests/canvas/prof.sh
@@ -0,0 +1,6 @@
+#!/bin/sh
+
+echo "*** LARGE ***"
+python performance.py large | egrep "(\(scatter\))|(\(draw\))|(tostring_rgb)|(fromstring)"
+echo "*** SMALL ***"
+python performance.py small | egrep "(\(scatter\))|(\(draw\))|(tostring_rgb)|(fromstring)"
\ No newline at end of file