Combining images with PHP GD

I want to combine some images with PHPGD to create a CSS Sprite dynamically, though I have a problem. I haven't worked so much with GD and I barely managed to do it, but the problem is the images occupy much more space after I combine them. I did a test with 3 images that have 13KB altogether. Af开发者_如何学JAVAter I combine them the final result has 42.5KB.

Is there any solution to this without losing quality ?

Thanks

well 13KB * 3 = 42 KB thats right =)

maybe: http://sheldon.lendrum.co.nz/php-gd-library-css-sprites_416/08/ or something else?

there are many css sprite generators for php around (sourceforge ...)