title: I want to resize a picture but python can't read the imagefile
body: <p>So I want to resize a picture in python using PhotoImage to show it with Tkinter. Eventhough it is a normal imagefile Python gives me the following Error: "couldn't recognize data in image file "./bucket/Background.pgm"".</p>
  
  <p>I've changed the file from jpg to png and finally to pgm but it didn't help. Paint.net can show me the file and Python can load and other files to. But when I want to resize it, it doesn't work.</p>
  
  <pre class="lang-py prettyprint-override"><code>from tkinter import *
  w=Tk()
  w.state('zoomed')
  
  bgpicture=PhotoImage(file='./bucket/Background.pgm')
  scale_w=int(w.winfo_screenwidth())/1920
  scale_h=int(w.winfo_screenheight())/1265
  bgpicture.zoom(scale_w,scale_h)
  bgpic=Label(w,image=bgpicture)
  bgpic.place(x=0,y=0)
  
  w.mainloop()
  </code></pre>
  
  <p>Expected: There should be a window with a picture as it's Background
  Result: Python can't load the image.</p>