diff --git a/pysstv/grayscale.py b/pysstv/grayscale.py
index d793e24..7377f74 100644
--- a/pysstv/grayscale.py
+++ b/pysstv/grayscale.py
@@ -16,9 +16,10 @@ class GrayscaleSSTV(SSTV):
     def encode_line(self, line):
         msec_pixel = self.SCAN / self.WIDTH
         image = self.image.load()
+        pixlen = len(image[0, line])
         for col in xrange(self.WIDTH):
             pixel = image[col, line]
-            freq_pixel = byte_to_freq(sum(pixel) / len(pixel))
+            freq_pixel = byte_to_freq(sum(pixel) / pixlen)
             yield freq_pixel, msec_pixel