During the last few days, I've played with dcb and its parameters a bit, mostly using test files supplied by the author of dcb (http://www.linuxphoto.org/html/test_download.html
), and compared it to the other demosaicing algorithms available in dcb_dcraw, looking especially at resolution/moiré/aliasing artefacts in the test charts.
My ranking in terms of these criteria would be
dcb Q=2 and dcb Q=5
I can't see a difference between dcb/Q=2 and dcb/Q=5 (even if I know where the differences are). In particular, I don't see any difference in sharpness/resolution/suppression of artefacts. dcb/Q=0 is only slightly ahead (imo) of ahd.
In terms of noise, I don't think that the -E option offers any benefits – the image loses sharpness, but subsequent denoising isn't any easier.
dcb is significantly slower than any of the other methods – for a 24 MPx image, I have obtained the following timings
2.6s linear interpolation
13.4 dcb Q=0
15.1 dcb Q=2
17.5 dcb Q=5
All running times seem to grow linearly with the number of pixels.
I haven't seen an example where dcb Q=5 performs worse than the dcb with Q<5. In view of the relatively small differences in running times, I'm wondering if anything but dcb/Q=5 is needed.
The noisy sample image shows that ahd has a tendency towards labyrinth artefacts in the presence of noise, while dcb/vng/ppg tend towards producing coloured blotches (which may be a bit harder to remove).
In real world images, I haven't been able to spot visible differences between AHD (my preference so far) and dcb/Q=5, so I'll probably keep the default to AHD because of its better performance. However, I'd love to have dcb/Q=5 as an alternative in case of moiré problems.
It would be interesting to test these algorithms on a very sharp raw image on a sensor without antialiasing filter, to see if dcb can extract more sharpness there than ahd.