I, too, use GIMP and highly recommend it. Since I am more of a developer than an artist I find myself often frustrated by Photoshop. It just doesn’t “think” in the terms I do.
Did you know Photoshop is available in an online edition?
I beleve png has more colours and so along with no compression the file size is larger.
You coud strip out the EXIF data which includes a thumbnail to save image size.
I use Gimp and Imagemagick which are both free and there are lots of other free programs.
I did some quick experimenting.
original 45KB
png 237KB
60 compression 12KB
Direct Copy
PNG Copy
Compressed Copy
I don’t know why the png is actually much heavier, from everything I’ve read and heard I would have bet it would have been less not more.
I am quite pleased with the higher compression. To my tired old eyes I can’t see much difference unless I “zoom in”. Then it looks blotchy.
I also noticed an option for “interlacing” that I didn’t (and have never) touched. Is that something worth playing with?
Currently I have a kind of “mini-logo” in the head that’s 100px w x 75px h ~4KB
I have photo “index pages” with thumbnails that are 125px w x 90px h ~ 10KB with from 9 up to a maximum of 22 thumbnails on a page.
The “gallery” photos are 400px w x 300px h ~70KB
On my dialup they don’t load that slow, but slow enough that I’m wondering if I should revisit them. Not everyone will have the patience for my photos that I have for them 
I don’t have Photoshop or Fireworks. I have an old OS and have been using PhotoRecall Deluxe - G&A Imaging Ltd. and MicroGrafx Picture Publisher 8
I don’t imagine they even come close to what’s available now. But I can set different compression ratios, save for web (I’ve been doing that already), and save (export?) as png.
So I’ll definately revisit this soon. Hearing from some pros that the compression ratio can be higher without too much quality loss is reassuring. And png support is much better now than it was years ago so I’ll look into that too.
Hello,
It depends on how they are being used. If they are images within copy, I usually limit them to 350px max. If its in a photo gallery 600x600 is pretty good because with the browser toolbars and website banners, that’s a good size. If they are much bigger than that it annoys some users. I usually set the compression to 6 or 7. The softer the image is the less it is effect by compression.
The most important things with jpegs is to “save for web” in Photoshop because it strips out metadata and thumbnails etc… The resulting file is often a fraction of the size of a regular save.
Michael
For elastic or fluid layouts I actually make images a bit bigger than I need to accomodate various screen resolutions. To compensate for the bigger dimensions, I reduce the quality significantly.
For JPEGs, I never use more than 60 (PS save for web panel). That is sufficient in most cases.
If an image allows me to use the PNG format, I don’t optimise in Photoshop at all but instead do it in Fireworks as there are plenty more and better possibilities to optimise images for the web, and the results in size are so much lower at times, it’s absurd.