Reduce polygon dataset file size and check image compression #41
Description
We have quite a few huge images in the Polygon dataset - for example some 4MP from Tretzendorf (12MB TIFFs, #31) and some 20MB+ PNGs (but only 9 MPx). These could be compressed and/or converted to JPEG without any significant loss of quality I think. The dataset as is is pretty hefty (70GB+) and there are about 4000/18000 images that make up 60GB of it.