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Following on from Brian Griffith’s explanation of some of the technical aspects of Sigma’s Foveon chip in use, I thought I would add some relevant user experience.

I converted over a hundred files from the SD14 over a few days. Not all of them very well it has to be said, but I got better at it. (This was individual treatment conversion, not batch conversion). I’ve even had a go at converting some files provided by a couple of correspondents (one of the good things about which is that you bring no pre-conceptions to the image. It is easier to see it, although it is harder to disentangle the effects of lenses, lighting etc). After discarding Sigma’s converter, I concentrated on Lightroom 1.1 and Raw Developer 1.7. There aren’t many (any?) other options, in fact, but for these purposes, the two converters that I was using were perfect. This is because they take opposing views as to how to best convert a Foveon file.

Superficially, the Lightroom conversions are the best. Absolute smoothness and nice bright colours. What this hides, though is a tendency to some horrid greens and yellows, and, critically, a loss of detail throughout the scene. What appears to be happening is a high degree of colour noise suppression or colour smoothing. But detail definitely goes too. Added to which, Lightroom has an extremely limited range of colour space options that mean it is difficult to take advantage of one of the Foveon strengths – pure, rich and subtly differentiated colour.

Raw Developer converts with an eye to detail preservation. As Brian Griffith pointed out, the inherent colour noisiness of the chip means that without the suppression, colour noise can be a problem, and a problem that gets worse with increasing ISO.

In practice, the Raw Developer conversions of ISO 100 files were clearly the better (although attention needs to be paid to the white balance setting which sometimes comes up awry on a default conversion). By better, I mean better detail without excessive contrast, and more neutral colours.

At ISO 200, Raw Developer conversions continued to be better, but only if a modest amount of work outside of the raw converter is acceptable. Particularly needed was some work on neutral shadows and black clothing to remove magenta colour contamination. I found that the Photoshop selective colour layer controls were ideal for this.

At ISO 400, Lightroom conversions were clearly the better. At this speed, the Raw Developer approach just couldn’t deal with the colour noise, whereas if you only ever used Lightroom then you wouldn’t be aware that colour noise was an issue. Subject to a little work on the yellow/greens the Lightroom conversions of ISO 400 files were fine, and, in fact, not very different from Lightroom conversions of ISO 100 files.

I didn’t try enough faster files to make a judgement.

For some applications this makes the SD14 an ISO 100 only camera. Certainly, used at ISO 400, you need to accept a loss of detail to deal with colour noise, and, with the current converters, you need to accept loss of control over colour space. This makes it look, to me, as if the current Foveon chip has no advantage, and a signficant disadvantage, over a Bayer chip for general purpose and mid to high ISO photography. Don’t forget that those heavily massaged Lightroom files are *only* 5 megapixels large, and interpolating them upwards just adds insult to their already injured status.

The files at ISO 100 look absolutely fabulous. At ISO 200 they can also look very good, but they sometimes need a little help.

For a niche dSLR this might all be acceptable. Very little that I shot needed ISO 400. I was more using 400 out of interest than anything. But for a general purpose camera, this noise, and noise/detail trade off is a serious limitation.

However, going back to where this started, for a shirt pocket camera this performance might well be crippling. And I wonder whether this is the reason that the DP-1 is still not released.

Some related posts chosen by the software:

• The Silicon Eye
• Pliny on the Sigma DP1
• Know raw? Part 2