I've noticed that two of the images I've uploaded recently have changed color somewhat and lost overall brightness and saturation. Both shots contain closeups of autumn leaves which are predominantly yellow with patches of red. The original jpegs on my system show well saturated yellows and reds pretty much identical to the leaves I actually shot. However, after upload to the site, the color saturation of the yellow was reduced, the reds had changed to dull brown, and the overall image was less bright. I compared the download from caedes at 640x480 on my monitor side by side with the original image to make sure I wasn't imagining something. The differences are very pronounced. Here are links to the caedes images:
http://www.caedes.net/Zephir.cgi?lib=Caedes::Infopage&image=Accipiter-1098323575.jpg
http://www.caedes.net/Zephir.cgi?lib=Caedes::Infopage&image=Accipiter-1097970626.jpg

Both these show the same red (original jpegs) to brown (caedes postings) changes in the and loss of saturation in th eyellows. However other images I've uploaded recently show no color changes at all. Any idea what is causing this situation? thanks...

The problem is probably in your colorspace. I believe the standard for web is still some kind of sRGB. If you upload a file in which some of the more saturated colors are present in your color space (say Adobe RGB, Colormatch) but are not present in the sRGB colorspace, those values will be represented as the closest approximation, usually a less-saturated version.
That being said, if you use Photoshop, you can click Image>Mode>convert to Profile and select sRGB. This may solve you problem.

You have a simple case of not color managing your digital workflow. The internet is not profile-aware, so the colors numerical values are used, instead of a perceptual conversion. The exif data shows that those were shot in “ProPhoto RGB" (which is new to me, so I am assuming it behaves similar to Adobe 1998.) "sRGB IEC61966-2.1" is what you want to convert it to (the standard for the web and most uncalibrated monitors), when following Sagelidiot's suggestion.

color profiles.. bah.. they cause problems at the presses..
SWOP printing and sheet fed printing is picky about calibration.. dot-gain profiles in greyscale images is just as bad
grr... yeah.. looks great on screen, but doesn't look half as good as it should on press.. i'd just discard the profiles

Thanks, folks! Although I haven't tested it yet, I'm fairly sure you're correct. I shoot raw files, and use Photoshop CS raw plugin to convert. My default colorspace for this is ProPhoto, which is the largest gamut color space available in CS. It is a larger space than sRGB. I've been saving the intermediate files in CS native format, then converting these to jpegs to upload to Caedes. But what I haven't done before uploading is convert the colorspace to sRGB. What I actually need to do for the Caedes stuff is convert the raw files in sRGB, then do all my edits in that space. That should give consistent results all the way through. Will give it a shot later this evening and report back.

Thanks again, all...that definitely fixed the problem! You can see the shot as it should look in new images...Waterfall Leaves 3. Compare this to Maple and Waterfall (the one that lost color)...huge improvement. I very much appreciate your accurate diagnosis!

Actually, I would leave the image in ProPhoto RGB while editing. This way you have more flexibility, and the colors will still come out a bit punchier. What I do for raw files is shoot them in Adobe 1998 (in camera setting), convert them using C1Pro, leave them as Adobe 1998, do all my editing, and finally I convert them to sRGB at the very end.

well, I think he intends to continue working in ProPhoto for his personal gallery, and by doing editing in sRGB he meant after converting to sRGB he would do any edits necessary to spruce up any color loss in the image in preparation for caedes submission.
am I wrong?

I'm glad that this was fixed quickly as I had no idea what the problem was. =)

noobguy: if the image is left in its native color space, edited (still in ProPhoto), and then converted perceptually to sRGB at the very end, there will be no color loss that needs fixing.

i'm really confused about this colourmanagement, because some of my pictures, out of my camera, or edited are already in sRGB, and some are in other profiles. i know i didnt change the settings on my camera, and it seems to have no correlation to whether i was shooting raw or jpgs, does anybody have an idea why some would be sRGB native, and others not?

cool deal, thanks will, I havent experimented with the transitions.

Possibly when you decoded the raw images, you set it to convert the images to another profile, as well. I don't believe that your camera allows you to set different spaces, so thats strange.

This has turned into a learning experience, which is an unexpected benefit. I've tried the workflow both ways...1) converting raw directly into sRGB then editing in that space and b) converting from raw in ProPhoto RGB, then converting to sRGB after editing. Did this with a close-up of some Maple leaves that has lots of bright yellows and reds, which were the colors most affected by my original "color loss". I can't tell any difference in the final 8 bit jpegs from workflow 1 or 2. However brphoto is correct that doing all the edits in the larger ProPhoto color space gives me the most options for the file. That is also the technique recommended by "Real World Photoshop" which is a pretty authoritative source. ::noobguy is also correct...I almost always end up with 3 copies of each file I work on: a) orginal raw, which I never alter, b) 16 bit .psd or .tif if I want to use the file later for something other than web and c) 1400x1200 jpeg for Caedes.

thats a really odd resolution dont you think? i've never seen a 1400x1200 monitor before. where do you live?? lol ;)

You're right, 1400x1200 ain't like any monitor I ever saw. But it is the largest of the sizes for image upload that caedes allows and the closest to the "native" format of my camera. I actually end up creating another copy of some jpegs for burning on CD, sending to friends, etc. Usually these are 800x600.

Don't you mean 1600x1200? 1400x1200 wouldn't be the correct aspect ratio.

ya, that one got me too, i looked at your gallery, and there are a few with borders, but not ones 200 pixels thick?

Oops, yeah its 1600x1200. I need to think before I type. You probably already know this, but...the borders on some photos are due to the aspect ratio of the imaging chip in my camera. Caedes assumes a 4:3 aspect ratio, where my camera has a 3:2 ratio. When I resize the width of the image to 1600, the height is usually about 1064. If I forced that to 1200 it would distort the overall image. So I take the 1600x1064 and paste it onto a 1600x1200 background. Images that I upload without borders have been cropped; when I crop I try to get as close to a 4:3 ratio as possible.

ya, but i was just confused, it would be different at 1400x1200, the borders would be vertical, which lacks in your gallery. but it was just a typo :p

I assumed it was a typo, and I believe Carl was thinking that as well when he posted. As for 1600x1200 screens, I know a few people with LCDs that large. And mine is 1400x1050, so that 1400 number is not *all* that wierd (1400x1050 is called SXGA+).

My res now is 1440 x 900. Seems weird to me...

Sam I take it you are still getting use the that new MAC?