Group, I've been trying to figure out the source of these horizontal line artifacts in x-trans demosaicing, but without much luck.
The artifact also appears with VNG, but Markesteijn seems to amplify it in two ways: 1) by reducing the number of other artifacts but not this one and 2) by increasing the horizontal extent of the artifacts by one or two pixels. I know the party line is just that "x-trans demosaicing will always produce artifacts", but I don't think that's what's going on here. X-Trans has a periodicity of 6x6. This artifact occurs at a period of 12 pixels, and seems to only repeat vertically. Aside from this issue, the Markesteijn algorithm does quite well. I've been poring over the code looking for something that could introduce an error at this period and have so far come up empty handed. Because VNG also exhibits this error, I think maybe the issue could lie in the common rawspeed code or some other shared part of the pipeline (in DT, dcraw and rawtherapee). Although most of that code seems to concentrate on the 6x6 matrix, so it's hard to imagine how it could introduce this error. I think better end results could probably be achieved by simply ignoring those two green pixels in every 12th row and just fully interpolating them, but that's probably not the right thing to do. I do wonder if images from the 1st generation X-Trans sensors also exhibit this artifact... Perhaps someone with one of these cameras could photograph a bird or a puppy with it in the interest of science? I have been unable to find any information on whether the PDAF pixel information from X-Trans II is included in the raw data or if the camera interpolates it out, or even where these pixels are located on the sensor (e.g. perhaps in rows separated by 12 pixels and always in the lower two pixels of the 2x2 green blocks which is where the artifact appears...) Frankly, considering that Fuji doesn't even bother to adjust the exposure of the high ISO RAW data themselves, it seems plausible that they just pass the PDAF pixel data through untouched. Also, I don't know if this is a known issue or not, but playing with the raw black/white levels produces some very weird looking results with X-Trans files. Another thing of note: There is a tag in the exif data: Fuji Layout : 12 12 12 12 I have no idea what it may mean, but it does mention the number 12... ___________________________________________________________________________ darktable developer mailing list to unsubscribe send a mail to darktable-dev+unsubscr...@lists.darktable.org
