Spectrograms - Am I missing something?

Question

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:

Here is the Python code.

def wavToSpec(wavefile,log=False,norm=False):
    wavArr,wavParams = wavToArr(wavefile)
    print wavParams
    return  mlab.specgram(wavArr,
            NFFT=256,Fs=wavParams[2],window=mlab.window_hanning,noverlap=128)

p, freqs, bins = wavToSpec("test.wav")
pylab.plot(p);
pylab.show()