If using svBuilder-Pro to create your galleries, deselect the 'Resize Images' checkbox in the 'Image Size' control panel (on the 'Images' tab) before adding images to your gallery and svBuilder-Pro will simply copy your original images across to the output gallery folder rather than resizing them first.
You can also edit a gallery's XML file and change the imageURL entries to point to whatever images you like.
You may also like to change the imageSmoothing Pro Option from its default value of 'true' to 'false' which may make your images look a little sharper.