I got into a discussion with my web design company about displaying images at 100dpi instead of 72 dpi. The images on our website at historicgolf.com are saved as 100dpi. Doesn't this take up more room than a 72dpi image? In fact I will copy the e-mail she sent me.

I discussed your concern with our developer and he provided further
clarification that I'm forwarding to you.

The dpi of the images on the site will not affect the download speed,
quality, or size of the images displayed. Images on a site display at 72
dpi. But dpi is used to indicate print quality of an image, not
site-display quality. In other words, you will not see any difference
between an image saved at 100 dpi displayed next to an image saved at 72 dpi
on a site.

The program we use to create the watermark image on the uploaded photo
creates the new image at 100 dpi. Again, this is an acceptable process
because the image will display at 72 dpi, regardless of the dpi at which it
is saved.

Hopefully this information answers your questions. Let me know if you have
any additional questions, or want to pursue changing the compression on the
thumbnail images.

It doesn't sound like there's a problem.

If you have any questions you might want to have them put up a web page on the site that displays both images right next to each other. Then you can load the page in your web browser and look at both images to see if you can tell a difference in image quality.

if you have 2 images - one at 72 and one at 100 and they are set to exactly the same dimensions on a website ie. both 200 pixels wide or whatever
then the 100 dpi file is going to be larger and take longer to load than the 72.
as far as I know all images should be converted to 72 for web use.(unless of course somebody is going to want to print high quality images from your site)

"The dpi of the images on the site will not affect the download speed,"

What a convenient answer but totally incorrect.larger dpi also means larger file size.

But then if both images display exactly the same dimensions on screen ie. visually they are the same dimensions then the file sizes will be the same.

But the 72 dpi will display better in this case as its optimised for screen use and will allow more compression.


[ Message was edited by: stevenjm 10/26/2003 04:25 pm ]

Let me hitch a ride on this topic. Does initial photo image quality make a difference? For instance, is there a diffeerence if I take a photo at at high resolution and then optimize for the web, or if I take it at low resolution and then optimize? Each of my products is unique, and I make a thumbnail at 3K and a clickable 15K version. Starting with less resolution would speed up the process a little, but I was wondering about the final quality. [I have stepped down resolution a little, and notice no difference in the final pic.]

I always like to start with the highest resolution available and end up with the lowest possible file size with the best quality still in it.

If I have a file that is already low quality I cannot effectively compress it and I cannot put quality back in that was never there, so the end result is a slightly higher file size... hopefully that makes some sense.. it works for me!

I find the same thing. for example if you resize an image to 200px x 200px at 72 dpi that was 300dpi to start with it very often looks better than one resized from say 150 dpi.