>"Paul Bullen" <paulbullen.com> wrote in message
>> I was recently set straight about resolutions of 72 dpi or ppi being
>> irrelevant to preparing images for the Web [...] But I now notice
>> that the first reference I was given [...] has this: "If your image is
>> intended for use on the Web, and not for printout, ...set your resolution
>> to 72 ppi...." I also notice that most of the books at Borders about
>> how to use Photoshop Elements give the same advice. Am I missing
>It matters. It doesn't matter. It's both at the same time.
>Sorry, it had to be said. :)
>One of the reasons it matters:
> * Using "72" for the resolution when scanning images will usually
>produce an image of about the right quality for display on a computer
>One of the reasons it doesn't matter:
> * As has been mentioned here recently (I forget who said it, otherwise I
>would have credited him...I think it was a him), all that really matters to
>the web browser is pixels. I'm not aware of a single web browser that
>attempts to reconcile the video driver's reported display resolution with an
>image's encoded resolution.
>The page on [url]www.scantips.com[/url] is a bit misleading. It's true that setting
>the resolution in an image doesn't affect how that image is displayed on the
>screen (usually...very few programs bother to look at that). But using 72
>dpi (or something similarly low) when you scan an image will avoid wasting
>time and disk space scanning at a higher resolution.
>What I do when scanning an image that I want for video display is to decide
>before I scan (if I can) how many pixels I want it to be. Then I set the
>scanner resolution appropriately so that the image I'm scanning comes out to
>be the right number of pixels. For example, if I'm scanning a 4x6 photo
>print and I want to fill a 640x480 screen (note that the width and height
>are reversed when talking about prints version talking about display screens
>:) ), then I'll want a resolution of anywhere between 100 and 120 dpi (using
>120 dpi will allow me to crop the scanned print so that it fits just right
>on a 640x480 screen; anything smaller and I'll have to stretch the image at
>some point or leave a border on the top and bottom).
>As far as web pages go, the best you can really do, using basic HTML, is to
>keep your page in proportion and let the user know what a good resolution to
>view the page would be. It's theoretically possible to use some server side
>code to scale images and other page content to be appropriate to the size of
>the browser window but in practice, I'm not aware of any sites that do this.
>It's a bit beyond what most people putting together a web site want to
>However, even in the case where I'm setting the scanner resolution (two
>paragraphs up) and the case where the server side code feeds
>appropriately-sized images, dpi doesn't really matter. What you really care
>about is how many pixels the image is versus how many pixels the screen is.
>You have no information regarding how large the screen is, so it would be
>pointless to try to factor in the screen's resolution. You just don't have
>Sorry...I think I'm kind of rambling. The bottom line is this:
>When scanning the image, you might as well aim to get the pixels into the
>computer at the exact size you expect to use the image. This fits in with
>your other question about resampling: you are correct, if you want to change
>the number of pixels in an image, you have to resample. You should avoid
>resampling, which is why it's better to scan at the correct resolution in
>the first place.
>Once you've got the image in the computer, with the number of pixels you
>want, the dpi resolution of the image is irrelevant. None of the programs
>showing the image on the screen will bother to look at the dpi resolution
>and you can set it to whatever you want. The only place the dpi would
>matter is if the image gets printed, and even there, most people wind up
>scaling images to some other specific size for the purpose of printing,
>which winds up overriding the dpi set in the image. You can consider the
>dpi set in the image as a suggestion, and nothing more.
>The most important thing, with respect to how good it looks when printed and
>with respect to whether it fits in your web site, is how many pixels are in
>the image. That's the one thing that is invariable. It's the one thing
>that is a fundamental characteristic of the data contained in the image.
>Everything else just relates the data in the image to the human concepts of
>p.s. One other reason to set an image not intended for printing to "72 dpi"
>is simply as a reminder to other humans that might have access to the image
>that it's not intended for printing. An image that's really only 72 dpi is
>going to look terrible on a printout. Again, this isn't something the
>computer cares about...it's just a way for one human to convey a message to