I'm noticing a small problem when using PS to edit, then output scans of slides for posting on the internet. What I do is eyeball the image that I want as I want it on the screen, then save as a JPEG to post on the internet. The problem is, what I see on the screen is not what gets saved to JPEG. There is the compression thing which is fine, but what I don't get is that the preview window in PhotoShop displays 'original' as the same as the JPEG as far as I can tell. The color is shifted and somewhat desaturated and sure enough, that's how the final image gets converted. I don't see the point of fine tuning images if this is the result. There is a way to get beautiful JPEGs with small file sizes but I don't know how. Is PS not the right tool for the job?

When you are working with images in Photoshop that you want to display on the web, you need to have their profile as sRGB as that is what browsers will display the image in which will give you differences if you have them in another profile like Adobe RGB.

Try it you will see the difference.