How can I reduce the file size of a photographic background image without losing quality?

I have a very large background image ~400k. If I reduce the quality in Photoshop to say (4) it will shrink it down to ~180k - still big but much more manageable. Are there any other good methods at reducing file size without losing a ton of quality? My PSD for my background image开发者_StackOverflow中文版 is basically a giant collage - some of the pics have color and the rest are desaturated. I'd love to save as black and white but need some of those color images.

Thanks for any help!

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have you tried to save the image in Photoshop by "Save for web and devices"?