And the file has a very, very faint gradient background with heavy dithering, so lossless compression won't actually help that much (ECT was only able to shave

And the file has a very, very faint gradient background with heavy dithering, so lossless compression won't actually help that much (ECT was only able to shave 13% of the file after minutes). In fact it is one of the worst imaginable cases for raster image formats.