Greetings,
I've been tasked with digitizing the following graph:

Original Graph.png

There are quite a few tools which allow one to calibrate axes and then get a series of points.
I have done this, and I have a data series for each curve. I've put them together on a scatter graph, yielding the following result:

Untitled.png

However, the issue is that the y-axis scale is different on the original image. Some measuring has shown that the distance between 1 and 2 is roughly equal to the distance between 2 and 4 so it's base 2 of some sort, but I have no idea how to replicate the original scaling.
If I set the y-axis as being logarithmic on Excel, I get a bunch of negative values as the original points I got go below one.
To top it off, technically the original points were already logarithmized (I'm assuming that's a word) - so technically I don't need to perform any mathematical operations on it, just have the scale not be linear.

Any suggestions?