Sigma/Foveon Questions
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From: nospam on 23 Apr 2010 15:52 In article <MPG.263c14a5c6f2df6c98c2aa(a)news.supernews.com>, Alfred Molon <alfred_molon(a)yahoo.com> wrote: > > No, there is no reason that such a design would have any particular > > spectral imbalance - you could have each photodiode of the appropriate > > response. The problem is there is no such control of the spectral > > response with the Foveon device. > > You are making some assumptions here, but have no way to know the > details of the Foveon implementation. there's plenty of documentation on how it works.
From: nospam on 21 Apr 2010 03:43 In article <YOxzn.108404$NH1.53444(a)newsfe14.iad>, Martin Brown <|||newspam|||@nezumi.demon.co.uk> wrote: > Luminance is inferred from the Bayer data based on the GR,BG matrix or > in some cases CM,YG matrix. The luminance is dominated by the green > channel and the red and blue provide minor corrections to it through > various cunning heuristics. that's not how it works. for any given pixel, it looks to at least the surrounding pixels (3x3) and maybe two levels out (5x5). beyond that isn't generally worth it. there is also no single algorithm either. an awful lot of pixels contribute to rgb of one pixel. > >> Having the sharp edges mangled by subsampling faults stick out like a > >> sore thumb in the handful of cases where it is relevant. > > > > not when it's chroma being subsampled. try it in photoshop. convert the > > image to lab and blur the ab channels. you only need to blur it with a > > 2 pixel radius to simulate bayer, but you can crank it to 5 pixels and > > not notice a difference. > > That depends. on what? i guarantee that you can't see the difference. > The red channel as reconstructed by standard JPEG decoders > can corrupt the luminance value by enough to be a nuisance in some > cases. It is only obvious when this situation arises which is typically > most obvious with fine black lines on near saturated red. This quirk is > part of the reason why JPEG images drift when recompressed many times. this isn't about jpeg decoding though. > I am no great fan of the Foveon sensor, but it does have an edge for > certain photography and might be what the OP is looking for. However it > also has its own problems so only he can decide if it is for him. that's true. unfortunately the types of photography for which it is suited are very limited.
From: Ray Fischer on 23 Apr 2010 03:18 Kennedy McEwen <rkm(a)kennedym.demon.co.uk> wrote: >In article <4bcfd38c$0$1647$742ec2ed(a)news.sonic.net>, Ray Fischer ><rfischer(a)sonic.net> writes >>Kennedy McEwen <rkm(a)kennedym.demon.co.uk> wrote: >>>In article <210420101542128471%nospam(a)nospam.invalid>, nospam >>><nospam(a)nospam.invalid> writes >>>>In article >>>><cd4821ed-e063-472e-b52f-2ca5bf5fd206(a)k33g2000yqc.googlegroups.com>, >>>>Bubba <digitalrube(a)yahoo.com> wrote: >>>> >>>>> > You didn't know that Bayer sensors have twice as many green pixels? >>>>> >>>>> No. That's why I post questions here. Why in God's name would they >>>>> have twice as many? >>>> >>>>because there are three primary colours that need to fit into a 2x2 >>>>grid. >>> >>>Nothing of the sort. There is no requirement for a 2x2 grid, the >>>colours could be arranged as triads, as in the dots on a conventional >>>colour CRT, or as linear triplets as in the lines of a Trinitron screen >>>or LCD & Plasma displays. >> >>They would be expensive and would reduce the number of total pixels. > >Not at all. The pixels can be arranged in a standard orthogonal grid >with the CFA grouping three pixels. And how is that different from a Bayer sensor? >>It would also require interpolation to translate to the ubiquitous >>retangular grid of displays and file formats. >> >Interpolation is inherent in all CFA formats Not spatial interpolation. -- Ray Fischer rfischer(a)sonic.net
From: Martin Brown on 23 Apr 2010 03:24 jgh wrote: > On Thu, 22 Apr 2010 07:48:15 +0100, Martin Brown wrote: >> You really do need to post an *example* of this mythical "red flare" you >> keep harping on about. > > I've seen an example posted. Somewhere. Maybe not in r.p.d though. > Subject was a welder in action (probably arc). Around the > highlight (and I could believe it was *very* bright, as the rest > of the image was exposed nominally) there was a square grid > of red blobs overlaying the scene, fading out away from the > highlight. There would have been on order of twenty blobs over > the height of the whole image, had they not faded. > > I wondered if the effect was a double reflection, from the sensor > surface then from a lens element surface. That was with the Sigma and Foveon sensor and is very clearly a problem specific to that particular technology (not Bayer mask at all). They appear to have a problem of a reflection of brilliant point sources off the front of the CCD and the back of the antialias filter casting coloured shadows of the front red filter mask onto the sensor. The link was posted in here recently. In one of the images I thought it actually enhanced the shot (the others like this sun image are dire). http://raist3d.typepad.com/files/sigmanotoksunclouds.jpg The welding picture is more exciting with the defect http://www.testiweb.com/images/jpg/digital_cameras/Sigma%20dp1/Jpg%20950x%20or%20lower/foveon_flares_2_SDIM0025_950x.jpg But this is not what the OP was on about. This is Foveon specific. Regards, Martin Brown
From: nospam on 23 Apr 2010 04:11
In article <WWbAn.202691$Ye4.177622(a)newsfe11.iad>, Martin Brown <|||newspam|||@nezumi.demon.co.uk> wrote: > That was with the Sigma and Foveon sensor and is very clearly a problem > specific to that particular technology (not Bayer mask at all). They > appear to have a problem of a reflection of brilliant point sources off > the front of the CCD and the back of the antialias filter casting > coloured shadows of the front red filter mask onto the sensor. there is no antialias filter in the sigma/foveon cameras. the red dot problem is from the infrared cut filter. |