Bitmapped images should be full size. Extracting proper vector graphics is a work in progress: https://github.com/arxiv-vanity/engrafo/issues/247

If you want to extract figures/images from PDFs, the best way to do it is to use Adobe Illustrator (or equivalent... Inkscape maybe?). That’ll let you extract full sized bitmapped graphics or arbitrary parts of the PDF as SVG vector images.