What's your browser & OS? RAM isn't the bottleneck here, it'll be the CPU via a poor JavaScript engine.

Of course, it's open source, any optimisation suggestions will be gratefully received. The calculation of sprite boundaries happens in two steps, first a contraction https://github.com/jakearchibald/sprite-cow/blob/master/www/... then an expansion https://github.com/jakearchibald/sprite-cow/blob/master/www/...