Image sizes are huge! Any way to include optimization settings?

First of all this tool is very helpful in generating all the image sizes needed for an app. The problem is, the output sizes for PNGs are huge (1.17MB+)! I had to re-export all the images using Photoshop with the PNG-8 setting. So, if an optimization setting can be added, it would be very helpful in reducing files sizes by 50% or more.
