Sigma/Foveon Questions
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From: Chris Malcolm on 21 Apr 2010 12:50 Bubba <digitalrube(a)yahoo.com> wrote: > On Apr 20, 5:04?am, Martin Brown <|||newspam...(a)nezumi.demon.co.uk> > wrote: >> >> The problem arises later in the imaging chain. Bayer sensor struggles a >> bit with a pure red (or pure blue) monochrome images because it has >> fewer independent pixels. Normally the luminance channel is able to hide >> these defects, but when the situation arises where the luminance channel >> is corrupted by the chroma channels then you lose detail. > Okay, now this interests me. I asked on other threads the obvious > question why a CCD sensor should be considered the equivalent of a > CMOS, if no very low-end P&S has a CMOS. CMOS has an extra on-chip wiring overhead which matters a lot in very tiny dense sensors, and not much on big DSLR sensors. The new back-illuminated CMOS sensors remove that CMOS overhead (to the dark side of the chip) and are bringing CMOS sensors into low-end P&S and phone cameras. > Why would green not be a problem? You didn't know that Bayer sensors have twice as many green pixels? -- Chris Malcolm
From: Bubba on 21 Apr 2010 18:30 On Apr 21, 12:50 pm, Chris Malcolm <c...(a)holyrood.ed.ac.uk> wrote: > > CMOS has an extra on-chip wiring overhead which matters a lot in very > tiny dense sensors, and not much on big DSLR sensors. The new > back-illuminated CMOS sensors remove that CMOS overhead (to the dark > side of the chip) and are bringing CMOS sensors into low-end P&S and > phone cameras. Does this mean (what someone reviewing a Canon SX1 said) that the CMOS sensors on $400--$500 P&S are "small" and (I suppose) mediocre? How can you tell which CMOS sensor a particular camera has, and whether it's any good? > You didn't know that Bayer sensors have twice as many green pixels? No. That's why I post questions here. Why in God's name would they have twice as many? I haven't bought a new digital camera in three years, because of something I read here back then about my particular problem--red channel flare--not ever improving in digital photography unless (three years ago) you could afford a splendiferously expensive camera ($+++Ks).
From: nospam on 21 Apr 2010 18:42 In article <cd4821ed-e063-472e-b52f-2ca5bf5fd206(a)k33g2000yqc.googlegroups.com>, Bubba <digitalrube(a)yahoo.com> wrote: > > CMOS has an extra on-chip wiring overhead which matters a lot in very > > tiny dense sensors, and not much on big DSLR sensors. The new > > back-illuminated CMOS sensors remove that CMOS overhead (to the dark > > side of the chip) and are bringing CMOS sensors into low-end P&S and > > phone cameras. > > Does this mean (what someone reviewing a Canon SX1 said) that the CMOS > sensors on $400--$500 P&S are "small" and (I suppose) mediocre? How > can you tell which CMOS sensor a particular camera has, and whether > it's any good? dpreview normally lists the size of the sensor. you can also determine it by comparing the actual focal length of the lens versus the 35mm equivalent focal length. the higher the ratio, the smaller the sensor. for example, the canon sx1 has a 1/2.3" sensor, which is much smaller than what's in an slr. the lens is a 28-560 equivalent but if you look on the lens itself, it's actually a 5-100mm lens, making the conversion factor 5.6. a typical slr is 1.5-1.6x, and you'd need an 18-375mm lens for the same equivalent. in other words, the sensor is tiny. <http://www.dpreview.com/reviews/canonsx1is/> > > You didn't know that Bayer sensors have twice as many green pixels? > > No. That's why I post questions here. Why in God's name would they > have twice as many? because there are three primary colours that need to fit into a 2x2 grid. there are a number of ways to arrange them, but doubling green produces the best results since that's where the eye is most sensitive. sony tried emerald as a fourth colour and kodak has a patent on using no filter (i.e., white) but i don't think that's in a camera yet. some cameras even used cyan, magenta, yellow and green. > I haven't bought a new digital camera in three > years, because of something I read here back then about my particular > problem--red channel flare--not ever improving in digital photography > unless (three years ago) you could afford a splendiferously expensive > camera ($+++Ks). do you have an example of this so called flare?
From: nospam on 23 Apr 2010 21:16 In article <GNrux+C+mj0LFwHX(a)kennedym.demon.co.uk>, Kennedy McEwen <rkm(a)nospam.demon.co.uk> wrote: > >>>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. > > > Yes, spatial interpolation - do you think the red and green content of > the pure blue pixels are created by magic? it's not spatial. the number of pixels on the image and on the sensor are the same. it's the toy cameras, such as the ones that advertise 640 x 480 but really have a 320 x 240 sensor, where there's spatial interpolation.
From: Bubba on 23 Apr 2010 21:21
On Apr 21, 8:35 pm, Kennedy McEwen <r...(a)nospam.demon.co.uk> wrote: > > Mismatched spectral response is one of the reasons why the Foveon > concept isn't as good as its supporters claim. Whilst you do get full > colour pixels, and hence increased resolution over a similar pixel count > BFA camera, the response is a poor match to the eye. Foveon's highest > response is to blue, then green and then red. With this major mismatch > in spectral response between the sensor and what we perceive, the Foveon > design requires significantly higher matrix manipulation to reproduce > the visual image, with its consequential tendency to excess noise and > colour balance errors across the human visual spectrum. Sigma cameras > are notorious for their inability to get consistent flesh tones. > > Kodak's proposed RGBW 2x2 matrix has similar problems, although it comes > with the benefit of improved broadband luminance response, so it isn't > all bad. Colour purity in good light isn't as good as conventional > Bayer, but low light sensitivity is much better. The thread has gone far beyond my ability to follow most of the responses. I appreciate the time you took to make this passably understandable by someone conversant neither in this specialized field of technology nor, for that matter, in film-based photography (if indeed any mathematical equations or matrices would pertain to film- based photography). Today, I handled the Nikon P100 model I spoke about somewhere on this thread. It's pretty lovely, but there's no review of it on dpreview, and I want someone to tell me if the sensor size make the "CMOS" lure (for laypeople such as myself) pathetic. Although nospam gave some sort of formula for figuring out how effective a sensor will be, this is Greek to me. So since I've left the Sigma possibility behind, if someone could tell me if the P100 sensor is comparable to the Canon SX1 (which is apparently very small), I'd appreciate it. I'd also appreciate knowing how small is too small with a CMOS sensor (if it's possibly to say that, i.e., below a certain size, I'd be better off, or just as good with, a camera with a CCD). Thank you. |