PNG vs JPEG Image Quality and File Size Comparision

by Craig A. Smith, 1999-12-24

Amazing but True

PNG-24 files are smaller than the smallest JPEG (Lowest Quality), but look better than the largeest JPEG (High Quality).  PNG-8 is limited to 256 colors, so not a good choice for continious tones (photographs).  Like the veritible GIF format, images saved as PNG are compressed - but without loss.  Before PNG, the only fault I could find with JPEG was that they aren't a good intermediate format.  Repeated Saves will degrade the image since a "lossy"  algorythm is used.  But unless you were editing the same image over-and-over, you could avoid this in practive by using High Quality until your final Save.  But now PNG offers smaller files with lossless compression and 24-bit color!  What will they think of next?

Strangness and Multi-Scan Images

Making a PNG "interlaced" will increases its size.  But making a JPEG "progressive" will decrease the size slightly.  Adding more scans shrinks it a tiny bit more.  In both cases, a blury proxy of these images load quickly, then shapens with progressive scans.  Phillip Greenspun ( is not a fan of progressive JPEGS, but Derick MeCulland (The PhotoShop Bible) likes the idea.  I've noted some problems saving these with earlier versions of PhotoShop, so I guess I've avoided them for practical reasons until now.  But the advent of PNG forces me to reasses these image formats.


To create PNG files with PhotoShop5.5,  be sure to "Save for Web."  If you "Save As" or "Save a Copy" into the PNG format then, although PhotoShop can still open them and browsers display in-line images fine, the latest browsers render a very "blackened" image when you to open just a PNG image (click to test).  Besides "Save for Web" yields slightly smaller files.