200K increase for xml -> pdf when using images

[Rick Roen]

FOP 0.92b Saxon 8 Barcode4j     I am doing an xml + xslt -> pdf via the command line using Saxon8 to transform.   When I produce the final pdf with no images the file size is approximately 25K   When I add two postnet bar codes, each of which are 1K png files, the pdf goes to about 225K.   Why does it grow so large?   I think I have read there is some problem if I were to use Barcode4j to produce an SVG file and put this in my transformation with 0.92, but does someone know if this would cause the same increase in file size?   TIA   Rick