There is currently a very interesting thread on the Luminous Landscape Forum, one that should be especially of interest to those who use commercial labs. Although the OP is about preparing an image for printing with Lightroom, the fifth post (by "Onsight") presents a wider view (a view that seems knowledgeable) and may be useful to anybody who uses these services:
http://www.luminous-landscape.com …topic=52469.msg431859#new![]()

