 <p>Tried exporting the same PNGs as 8-bit PNG and the filesize has reduced significantly.</p> <p>Steps:</p> <ul> <li>Open the PNG in Photoshop</li> <li>File > Save for Web and Devices</li> <li>Select "PNG-8 128 Dithered" from the "Preset" dropdown</li> <li>Save</li> </ul> <p>Reduced a 31kb image to 10kb.</p>