By default, svBuilder-Pro creates JPG images of 1024 x 768 at a quality of 80%.
However, this can be changed by clicking the 'Change...' button in the 'Image Size' control panel on the 'Images' tab.
Try increasing the quality to 90%. Much higher than this usually does not have much bearing on the visible quality of the image but produces a much larger file size.
Alternatively, you might want to create your own JPG images for use in the gallery (rather than have svBuilder-Pro rescale your originals). If you wish to try this, just deselect the 'Resize Images' checkbox before adding images to your gallery.
One further thing that might help is to change the imageSmoothing option from the default value of TRUE to FALSE.
In svBuilder-Pro, this option can be found under 'Customize -> Main Image'.