IF Function and Measure

I am trying to embed an image in a table to show some KPI's based on whether sales are up or down.

In order to do this I have formula as a measure to calculate the change in values to prior reporting week by client

% variance -1 v -2 = 
DIVIDE(SUM('Bookings'[-1 week rev])-sum(Bookings[-2 week rev]), SUM('Bookings'[-2 week rev]))

I am then using an if statment to return the correct image;

Column = IF([% variance -1 v -2]<0,"http://icons.iconarchive.com/icons/visualpharm/must-have/16/Stock-Index-Down-icon.png","http://icons.iconarchive.com/icons/semlabs/web-blog/32/arrow-up-icon.png")

Which in a way works...but sadly it returns both the positive and negative of the IF statement so for each client I have different results and the differing images showing. Without the IF statement, the formula works perfectly. Can anyone please shed any light on what I appear to be doing wrong?

TIA