Web graphics at different resolutions

Testing file sizes of images saved at 72 dpi vs. 600 dpi. GIFs and PNGs are approximately the same file size regardless of the image resolution. Based on discussions at MetaFilter and TalkGraphics.com.

Photoshop’s Save for Web reduced the resolution of all of the images to 72 DPI regardless of the initial setting; using Save As retained the initial DPI settings.


File type:	GIF
DPI:	72
File size (bytes):	303


File type:	GIF
DPI:	600
File size (bytes):	309


File type:	JPEG
DPI:	72
File size (bytes):	537


File type:	JPEG
DPI:	600
File size (bytes):	2,284


File type:	PNG
DPI:	72
File size (bytes):	1,880


File type:	PNG
DPI:	600
File size (bytes):	1,880

Methodology

In Photoshop 6.0.1’s New dialog box, set height and width to 20 pixels and resolution to either 72 or 600 dpi (RGB Mode)
Use the paint bucket to fill the entire image with a web-safe color
In Photoshop’s Save As dialog box, save as GIF, JPEG, or PNG, accepting default settings
Repeat steps 1–3 for each image