Comparing the 2 might help you a bit from this site you might get to know a little bit more about the different types of file extensions.
http://www.scantips.com/basics09.html
TIF RGB - 24 or 48 bits,
Grayscale - 8 or 16 bits,
Indexed color - 1 to 8 bits,
Line Art (bilevel)- 1 bit
For TIF files, most programs allow either no compression or LZW compression (lossless, but is less effective for 24 bit color images). Adobe Photoshop also provides JPG or ZIP compression too (but which greatly reduces third party compatibility of TIF files). \"Document programs\" allow ITCC G3 or G4 compression for 1 bit text (Fax is G3 or G4 TIF files), which is lossless and tremendously effective (small).
PNG RGB - 24 or 48 bits,
Grayscale - 8 or 16 bits,
Indexed color - 1 to 8 bits,
Line Art (bilevel) - 1 bit
PNG uses ZIP compression which is lossless, and slightly more effective than LZW (slightly smaller files). PNG is a newer format, designed to be both verstile and royalty free, back when the LZW patent was disputed.