Bart,I thought that sharpening always enhanced edge contrast (i.e. added halos), but if done properly the halo is imperceptible.
Hi Henry,
No, fortunately there are better sharpening possibilities than USM (which
does) boost ege contrast). Deconvolution sharpening restores the orignal image's sharpness. However, it is not flawless because some of the information is alrady lost, so it requires a bit of restraint if it creates the basis for further enlagement.
Depending on the tools, sharpening in Photoshop can be best done on a luminosity sharpening layer with a blend-if adjustment that avoids clipping due to oversharpening. It also reduces the risk of halos spoiling the fun. Smart sharpening is using a sort of deconvolution sharpening, but there are better tools for that operation.
I always resample my enlargements using bicubic smoother in Photoshop. Since I am talking about printing 20-feet wide here my up sampling is often significant.
Bicubic smoother is not bad, but there are better methods available. Commercial programs like Qimage or Photozoom Pro are capable of higher quality resampling, and the free ImageMagick command line tools (using the Mitchel Netravali filter settings) in general also produces better results than Bicubic Smoother does.
My concern is that when you print huge prints that need a lot of resampling that you need to think about sharpening in a different way.
I fully agree, hence my suggestions.
Cheers,
Bart