Love this thread. This stuff is pretty over my head but I can hang enough to be curious and want to learn more. Now I understand what you were talking about the other day Bruce, mostly anyway.
If with a full resolution but slightly more lossy compression applied only to chroma you churn out files exactly the same size as those with far lower chroma resolution -- you have a far better image at no cost!!
Why hasn't this happened yet? (aside from our inability to clone Graeme) Would it be heavier on processing than sub-sampling? What's the deal?