Add signed log10 stretching

[erikmannerfelt]

I don't know what to call this filter, but I've been thinking of a log10 filter that preserves signs for quite some time.

sign = np.sign(data)
minval = 4
data = np.clip(np.log10(np.abs(data) + 10**(-minval)) + minval, 0, None) * sign

In this case, 1e-4 would be the smallest perceptible value and it would scale in log10 in both directions afterward.

This preserves the positive/negative directionality (as opposed to abslog) but still converts it to a dB-like scale. Very good for visualization!