Spectrogram - Am I missing something? I have the following signal:



I'm trying to compute a Spectrogram algorithm, but, don't think I'm doing it right.. 

I have computed the following:

1) STFT (size 256 with an overlap of 128) 
 2) Computed the logs using: '10 * log10(sqrt(re * re + im + im) 

This is the result that I get:



But when I use pylab in Python (for the same signal):
  x = pl.specgram(signal)

I get the following result:



Using the matplotlib I get the following:



Obviously, these are very different results.. I don't know why I'm getting these, I'm new to signal processing and spectrograms. Hope someone can help

EDIT:

This is the result I have when doing imshow in python:
This appears to be just a matter of projection. Try "imagesc" in matlab.