I managed to get hold of some stronger filters to push this trial as close as I could to what was expected, and it turns out it's not a valid option (not with my results, anyway).
The results highlight an issue I was made aware of on another forum; that of a poor performance of the Foveon with regards to colour separation. You CAN get each channel to produce similar response to filtered white light, but by that point you've lost any hope of the colours recorded being remotely accurate.
I would recommend buying the research edition of RawDigger. Then you will be able to open X3Fs and see a 3-channel histogram of the raw data in the image or part thereof. Here's a SD14 white card shot:
The x-axis is in EV. The SD14 raw data saturates up around 8000, so I could have gone another 1/3 EV in the shot. (Please don't tell me about the 12-bit ADC, Sigma does quite a bit of scaling in-camera and the raw data is written in unsigned 16-bit format.)
Notice that the sensor channel differences are not that bad when you consider that the lamp is a domestic CFL and, of course, that the raw data is not in RGB color space and neither is it white balanced which is why 'green' is a little higher than the other two channels.
So, your concerns seem to be more about SPP or whatever converter you use. The conversion transforms are of necessity extreme compared to Bayer.
I also hit the same issue trying to find UniWB. Fruitless.
I used UniWB as the custom WB on a SD10 for a long while. I followed Luijck's instructions to the letter, took the screen shot and it worked a bit but not enough for my shots to show that much difference.
I think Darr's bracketing approach is probably the only sensible one!
Indeed, bracketing works and is easy to do.
As to improving DR, the sad part is that the Foveon blotching is intrinsic to the technology. On the F19 (Polaroid x530) sensor it can even occur at mid-tones, giving a DR of, like, 1EV
. With later sensors and SPP making it's best efforts, you might get as much as a 4EV shot . . . or you might not. Of course, Foveon blotching isn't really "noise" as we understand it, more like artefacts I suppose. And, as I've said elsewhere, SPP is the finest de-blotcher on the planet, whereas DCraw is definitely not
best regards,
Ted