i have read that images for the web should be 72 pixels per inch...
You read incorrectly or you were reading the writings of someone without a clue (most likely the latter case).
Web images are measured by the number of pixels tall by wide. There is no other resolution data needed.
'72' is a default value that Photoshop uses when there is no resolution defined. It means nothing.
Google for the '72 dpi myth'
You do not have to change the images pixel count but it will reduce your file size which in turn reduces the upload time for the viewer.
You can do this by:
Image>Image Size - then change the resolution.
Also use the save for web option: File>Save for web & devices...
This helps with file size as well.
thanks for the responses everyone cleared up a lot...
so I was reading that the human eye can't distinguish past 300 pixels per inch for printed images... so using 400 pixels per inch for print would be uselesss...
does the SAME CONCEPT apply to web images at 72 pixels per inch? say I have an image with 300 pixels per inch I am using for the web... am I just making load times slower when I should make it 72 pixels per inch? is this a common practice to degrade images like this for the web?
hmmmm... i see when I do a save for web and devices that it saves it at 72 pixels per inch... i guess this is the optimal way to do things for web images in internet browsers???
but my file only went from roughly 1.6mb to 1.2 mb when changing from 300 pixels per inch to 72 pixels per inch... i dont think this would make much of a difference for load times even if i was using the image for JQUERY simple animations... what do you guys recommend?
as marian said the 72 dpi is a myth.
Make a standard for your image quality and stick with it I say. If I have an image that does not look good to me on one of my sites, I make sure I fix it.
1mb file? what are the dimensions of that thing?
"hmmmm... i see when I do a save for web and devices that it saves it at 72 pixels per inch."
Nor exactly. The ppi setting in the Document Size area is nothing but an instruction to the printer to print 72 (or whatever) of your pixels to each inch of paper if you decide to print it. This info is meaningless on the web, so "Save for Web" strips it and other data from the file, and that helps make the file size as small as possible. If the file is re-opened later on, Photoshop can't find the missing ppi data, so it plugs 72 ppi back into the "Document Size" box.
cool alright thanks everyone... i will go on my own little PS mission trying to inform people of the 72 pixels/per/inch myth now... that is doesnt degrade rather just strips resolution info...
and i will also "save for web and devices" everytime and do things correctly when preparing images for the web...
thanks again everyone... it has been a very informative day ...