Edit: Upon a bit more investigation, this black halo is NOT present when using DPP. Might this be related to Lightroom 4? Will have to go back and double check my LR4 settings and report back.
The issue looks like either a sharpening or possibly a demosaicing artifact to me. Keep in mind that, with RAW, the Cameras "Sharpness" setting is actually applied in post, either as part of demosaicing, or simply as a base sharpness setting (depends on the RAW processor). I know Pedro used a camera sharpness setting of 3...not sure what Bosman used. I would try dropping that to ZERO, see if the problem persists. If the RAW processor factors in the camera sharpness setting during demosaicing, then that might be the problem. I would try alternate RAW processors, particularly one that allows you to configure the demosaicing algorithm, and see if that may be the problem. There are a variety of free RAW processors, some that work for windows, many that only work for Linux. At the very least, you might be able to identify a demosaicing bug to report to whoever owns the tool(s) your using...either Adobe (ACR/LR) or Apple (Aperture) (as I presume you guys are using one of those.)
(If you want to give a Linux one like DarkTable a try, you could always pick up a preinstalled Linux Virtual image for VMWare Server and use a virtual machine on your windows dekstop.)
If it was a JPEG, thats a whole different story than RAW. JPEG images are inherently processed, and compressed. An in-camera JPEG with halos would indeed be Canon's problem though, which is kind of a bummer.
Edit: Upon a bit more investigation, this black halo is NOT present when using DPP. Might this be related to Lightroom 4? Will have to go back and double check my LR4 settings and report back.
Your LR settings are indeed a issue. Reset them to zero. If you have LR set to apply a ton of sharpening on inport, reset it to apply just a little, or none at all depending on the ISO.
Your LR settings are indeed a issue. Reset them to zero. If you have LR set to apply a ton of sharpening on inport, reset it to apply just a little, or none at all depending on the ISO.