I have an issue when importing NEF images to Photoshop CS4. Apparently featureless backgrounds have strange, kind of "worm-like" structure on the single pixel level. Since these artifacts are a bit periodic in nature, sometimes they interfere also on a more sensible scale.
The interesting part is that when I use UFRaw for importing, it seems that these artifacts are colour interpolation related. I've attached an image as an example (taken with a Nikon D40 + AF-S DX 35 mm / 1.8G lens: the top row contains samples of a white background, the bottom row samples a button feature. The first column is from Photoshop CS4, the second uses UFRaw's AHD colour interpolation, the third - UFRaw's VNG4C colour interpolation and the last column is again produced with Photoshop CS4 but a 1.0px sized Gaussian blur is applied since the images produced by UFRaw seem to be somewhat less resolved. Ignore the Moire patterns from the fabric.
All settings were kept at their defaults, affecting the image as little as possible, except for the "Colour noise" reduction option in Photoshop, which was set to 25 by default. Lowering it produces similar result to UFRaw's AHD.
Could someone would explain, where do these patterns come from and how to control them in Photoshop? Selecting a different colour interpolation algorithm in UFRaw helps, but I'd prefer to work with a single tool (Photoshop).
Thanks in advance.
It looks like you may be seeing the dreaded maze pattern caused by the two sensor green channels being out of balance:
Here is an explanation for a different camera as well as a solution if you also use CornerFix:
Such things can also be fixed in the Camera RAW but someone at Adobe may need to see samples:
Here is another Adobe Forum discussion:
Here is someone with a D40 that shows the patterns:
If you don't get a response from Adobe with this thread, I'd suggest reposting with the subject of D40 Maze Patterns and a link where people can download a sample DNG or original RAW. If you don't have your own file-hosting space, you can use somewhere like http://www.yousendit.com/ to e-mail yourself a download link, then post that link in the message.