On 24/01/07, Peter Lacus <[EMAIL PROTECTED]> wrote: > Even ACR with its magical Color Noise Reduction Tool failed to correct > these artifacts completely. What do you do when it occurs to you? Use of > lower quality lens would probably help as such lens will provide > additional anti-aliasing filter on its own, but I don't believe that > those are so-called digitally optimized lenses... :-)
>From recollection the AA filter in the *ist Ds was a higher frequency than the *ist D which many complained wasn't as "sharp" as its contemporaries from other manufacturers, there's always a trade off. The fact is that most decent lenses stopped down a little will out resolve the 6MP DSLRs so if the AA filter has been selected to provide a bit more apparent sharpness some occasionally aliasing in the captures will be the outcome. How the camera's processor or RAW file convertor software manages it depends on how "clever" the software is. Personally I've rather the camera was engineered to minimize the occurrence however in certain conditions (which you found) occasionally even a spacial frequency of multiples of the native resolution will cause visible aliasing. As others have mentioned the crops are dark but of course that's nothing to do with the aliasing which is plainly visible as a rainbow across the grille of the right vehicle after auto-level adjustment. Looking at the blue bus sign at the rear it's obviously that the grill bar frequency is far less than the system resolution, so in this case I'd suggest that it's more a problem in the RAW convertor, ie how it deals with regular high frequency pattern data. The colour noise reduction tool isn't designed to manage aliasing errors, it's primary purpose is to manage chroma noise which becomes more prevalent as ISO is increased. It's really a case of suck it and see, sometimes RAW software doesn't behave the optimally so we have to compromise. In the case of the radiator grille I'd simply create a rough mask and desaturate it. Cheers, -- Rob Studdert HURSTVILLE AUSTRALIA Tel +61-2-9554-4110 UTC(GMT) +10 Hours [EMAIL PROTECTED] http://home.swiftdsl.com.au/~distudio//publications/ Pentax user since 1986, PDMLer since 1998 -- PDML Pentax-Discuss Mail List PDML@pdml.net http://pdml.net/mailman/listinfo/pdml_pdml.net
