On Mon, Dec 12, 2016 at 10:40 AM, Ingo Liebhardt <ingo.liebha...@ziggo.nl> wrote:
> Hi all, > > Maybe you still remember that I tried an alternative approach to X-Trans > demosaicking (using guided filtering) in March / April this year… > In the end, I was not satisfied, and I gave up on that approach. The > problems were comparable to the Markesteijn algorithm, and the improvements > marginal. > > After giving up on that approach, I was again browsing conference papers > trying to get some inspiration. > I came across the work of E. Dubois, which looked promising. > It is promising, not so much when applied alone, but very much so when > combined with a gradient based approach like Markesteijn. > > I like Jo’s xtrans fringes profile a lot, but the colors get somewhat > muted, overall. > > Contrary to my first approach, this one finally seems to give reasonable > results. > I managed to get good output for the redline bug #10333. > You can have a look here: dropbox link > <https://www.dropbox.com/sh/un1y11uimbqxjjk/AAD3L-Rs9-ztwyBIm4rnCzK-a?dl=0> > > This is the output just with demosaic + base curve, nothing else. > > If you want to try some nasty X-Trans images yourself, I made a little > proof-of-concept. > This in form of a fork of darktable, which you can find here: > https://github.com/ILiebhardt/darktable.git > For trying, just compile, deactivate openCL (only C code thus far), and > choose ‚1 pass Markesteijn‘ as demosaicking method (doesn’t work for > 3-pass, and wouldn’t really yield advantages, either). > > Have fun trying, and let me know if you think that this one’s worth > pursuing further (only quick hack so far, and the used correlation filters > are a slow, naive implementation O(m n p q)). > > If you’d like to read some basics concerning the idea, I made a mini-blog > here: http://xtransdemosaicking.blogspot.nl > > Cheers, > Ingo > > > P.S.: concerning my previous approach, J Liles spotted single > pixel artifacts. I found out that these are not related tot the > demosaicking as such. X-Trans 2 and X-Trans 3 have hybrid AF, and the > pixels used for phase detection show higher noise. These are all green > pixels of a 4-group of pixels; never a red or blue, and never a solitary > green. But solving this would be a whole different project... > > > > > > > ___________________________________________________________________________ > darktable developer mailing list to unsubscribe send a mail to > darktable-dev+unsubscr...@lists.darktable.org > Ingo, Great to hear you're still working on this! I haven't reviewed the code of the algorithm, but I did give it a try on a few images. Here's one in particular (lots of sharpening added to make the differences more obvious.) http://www.nevermindhim.com/liebhardt-test Direct image links: http://www.nevermindhim.com/files/liebhardt-test/6acffe60-09c5-11e6-93d7-178612e3e7eb_E1_VNG.png http://www.nevermindhim.com/files/liebhardt-test/6acffe60-09c5-11e6-93d7-178612e3e7eb_E1_Markesteijn.png http://www.nevermindhim.com/files/liebhardt-test/6acffe60-09c5-11e6-93d7-178612e3e7eb_E1_Liebhardt.png My first impressions are: 1) (obviously you know this) It's slow 2) It introduces a hue shift 3) It does a better job of controlling color noise than VNG or Markesteijn. 4) Artifacts are similar in structure to Markesteijn (maze-like) 5) There is an additional textile like artifact that Markesteijn doesn't exhibit. 6) It overshoots in interpolating across gradients, but not as much as VNG does. If you can get rid of the textile effect and, color cast, and speed it up, this looks like it would be an improvement over Markesteijn (with no color smoothing/noise reduction). It's already looking more "film like" ___________________________________________________________________________ darktable developer mailing list to unsubscribe send a mail to darktable-dev+unsubscr...@lists.darktable.org
