So far I haven’t seen any advantage in terms of “worms”, both algorithms seem to perform the same on foliage or rocky textures.
The only advantage I see with the FDC algorithm, is in some areas of fine diagonal patterns (such as fabric), but it comes at a cost in color bleeding/blooming and some color aberrations in some fine pattern cases.
Here are comparaisons of FDC and Markesteijn’s 3-pass algorithms from Darktable (“DT-FDC” and “DT-Mar”, respectively) as well as the Markesteijn implemention in RawTherapee (“RT-Mar”). I processed some files from X-T1 (16 Mp) and X-T2 (24 Mp), trying to get the same solor rendition between DT and RT by using the standard color matrix and disabling any tone curve. You can download the resultaing files there.
Here, I’ll show some animated images (I applied the same tone curve to each image in Gimp, to add some contrast).
Some benefits from FDC in fine patterns:
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X-T1:
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X-T2 (the benefit is almost gone):
Some drawbacks of the FDC (color bleeding):
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X-T1:
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X-T2:
and color moiré:
Form these test images, the difference between DT’s and RT’s implementation of the 3-pass Markesteijn is microscopic.