Rotate an image in wxPython. Not working quite right

wxP_rotate.py

# -*- coding: utf-8 -*-
"""
Created on Thu Apr 04 14:01:09 2013

@author: jrobins
"""


import wx

class MyFrame(wx.Frame):
    def __init__(self, *args, **kw):
        wx.Frame.__init__(self, *args, **kw)
        
        

        self.bitmap = wx.Bitmap('frontcv22.png')
        self.image = self.bitmap.ConvertToImage()
        self.img_height = self.bitmap.GetHeight()
        self.img_width = self.bitmap.GetWidth()
        self.img_center = (self.img_height, self.img_width)
        print self.img_center
        
        wx.EVT_PAINT(self, self.OnPaint)
        self.Bind(wx.EVT_TIMER, self.OnTimer)
        self.counter = 0

        self.Centre()
        self.timer = wx.Timer(self)
        self.timer.Start(50)

    def OnPaint(self, event):
        self.dc = wx.PaintDC(self)
        self.dc.DrawBitmap(self.bitmap, 0, 0)
        
    def OnTimer(self, event):
        self.counter += .1
        self.bitmap = self.image.Rotate(self.counter, self.img_center).ConvertToBitmap()
        self.dc.Clear()
        self.dc.DrawBitmap(self.bitmap, 0, 0)
        

app = wx.App(False)
frame = MyFrame(None, -1, "Rotate")
frame.SetSize(wx.Size(400, 400))
frame.Show(True)
app.MainLoop()