Sigma/Foveon Questions

Discussion in 'Digital Photography' started by Bubba, Apr 17, 2010.

  1. Bubba

    Guest Guest

    strange, how despite that, foveon has a roughly 3 stop noise penalty.
    not necessarily. foveon is much worse.

    anything else is pure speculation.
     
    Guest, Apr 30, 2010
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  2. Bubba

    Martin Brown Guest

    It doesn't only capture 1/3 of the information. It is actually quite
    tricky to put an exact number on the amount of information that it does
    capture. But based on the 0.30, 0.59, 0.11 weights for R,G,B a Bayer
    quad captures (0.3+2*0.59+0.11)/4 = 0.40 or 40% of the information.

    Experience has shown that as long as the luminance signal has close to
    full resolution (and Bayer demosaicing ensures that) the lower
    resolution chroma information is invisible to the human eye except in a
    few special test cases. TV broadcast has exploited this for decades.
    Actually it is after a fashion almost optimal. It measures the essential
    components needed to reconstruct a full colour representation of the
    image in an efficient manner.
    Not when the sensors are so much smaller and seem to have nasty
    artefacts if there are specular highlights in the FOV.
    It does depend very strongly on the adjacent pixels that is true unless
    the image is undersampled which is what the antialias filter prevents.
    Only on the resolution of colour detail. Bayer is not prefect but it is
    nowhere near as good as the Foveon marketeers would have you believe.
    You seem to swallow their all their PR bullshit hook, line and sinker.
    But after it has been through the lens and formed an image on the sensor
    it is already limited by the MTF of the lens. It is theoretically
    possible that sub pixel colour detail that was resolved by the lens and
    lands on the wrong cell will be lost.
    That isn't it at all. The lens produces an image which is continuous
    over the length scales of pixels. The adjacent pixels are a very good
    predictor of the value in the middle.
    Bayer images are not soft at the pixel level. Certain manufacturers of
    P&S deliberately oversharpen their images because they know what sells.
    Same is true of TVs in shops with visible ringing on edge transitions
    and heavily posterised colours. That is apparently what customers want!

    You are flogging a dead horse with Foveon. It had its chance and did not
    make the grade. WHat it does is largely irrelevant unless you spend your
    life photographing colour test charts intended to prove how good it is.

    The human eye doesn't see fine colour details very well and if the
    luminance signal is good the perceived sharpness is dominated by that.

    Regards,
    Martin Brown
     
    Martin Brown, Apr 30, 2010
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  3. But the question is, what the performance of the sensor is. It may well
    The system performance is what matters in the end, everything from
    subject, atmosphere, optics, AA & IR filters, sensor, processing, display,
    viewing environment (e.g. light-level, vibration), eye optics, image on
    retina, brain performance. Probably even more factors. Of course the
    sensor matters, but it needs to be considered along with the rest of the
    system.

    As the eye can't resolve pixel-level changes of colour, for use with human
    perception to make a sensor which can do so could be considered
    over-engineering.

    For typical use, the Bayer sensor has adequate performance at an
    affordable price, and is certainly not a linear factor of two down in
    sensor resolution. Otherwise you would need a 17MP Bayer sensor to equal
    a 4.3MP Foveon one, and that doesn't match up with most reports. Of
    course, you can probably find special-case exceptions, and if your imaging
    needs fall within those exceptions, you choose the most appropriate tool
    for the task.

    Cheers,
    David
     
    David J Taylor, Apr 30, 2010
  4. Thanks. Alfred.

    Given the choice of today's 4.6MP Foveon camera or a 10-12-15MP Bayer
    camera, there appears to be an obvious resolution gain in the Bayer
    camera, plus the better high-ISO performance others have reported.

    60MP would almost certainly be overkill for what I do, and for what many
    people do with their photography. You choose the tools according to your
    needs.

    Thanks for your clarification in your last paragraph. It appears that the
    resolution loss with Bayer is around 1.3 (linear) from your first
    paragraph.

    Cheers,
    David
     
    David J Taylor, Apr 30, 2010
  5. Bubba

    Guest Guest

    it's actually not a big problem. the conversion from foveon samples to
    rgb is one of the big problems with foveon and why it's noisy and has
    inaccurate colour.
    no. the reviews say it *looks* like 8mp.

    just look at the resolution charts, it does *not* resolve as well as an
    8mp camera due to aliasing. people confuse real detail and accurate
    resolution with false detail and alias artifacts.
    nonsense. neighboring pixels are not wildly different from one another.
    they don't, and if they did you couldn't see it anyway.
    who cares? people want to look at photos, not individual pixels.
     
    Guest, Apr 30, 2010
  6. Bubba

    Guest Guest

    very small errors which most of the time will never be noticed.
    bayer does poorly on red/blue test charts. otherwise, it does very well.
    bayer was 10 mp about 4 years ago.

    canon's entry level camera *now* is 18mp. nikon's high end is 24mp.

    even if you think 4.6 looks like 8, it's way behind.
    most people don't.
     
    Guest, Apr 30, 2010
  7. Bubba

    Ray Fischer Guest

    Completely wrong.

    Once again: Images have a high degree of redundancy. The Bayer
    sensor captures far more than 1/3 of the needed information. Emprical
    tests show that it's more like 60%. Further, the much higher
    resolution of most Bayer sensors more than compensates.
     
    Ray Fischer, May 1, 2010
  8. Bubba

    Ray Fischer Guest

    Do even know why that's a silly statement?
     
    Ray Fischer, May 1, 2010
  9. Bubba

    dj_nme Guest

    If it followed the current Sigma and Foveon image sensor design
    practice, it would be missing an anti-aliasing filter and produce
    mountains of moire (false detail and "stair stepping")that would kill
    the alleged "advantages" that you are hoping for.
    I would hope that you look at the images it produces and note how much
    more moire (false detail and "stair stepping") there probably would be
    when compared to a similar resolution camera with Bayer CFA sensor.
     
    dj_nme, May 1, 2010
  10. Bubba

    Guest Guest

    actually, a little before nyquist, but he's right, foveon images are
    full of false detail and moire patterns.
    bayer doesn't cut off at 1/2 nyquist.
     
    Guest, May 1, 2010
  11. I also wouldn't buy the Sigma 4.6MP camera, because it does not have
    For the final image, I don't think I care in the least bit where the
    pixels come from, be it Bayer or Foveon, providing the end result is good
    enough, and that's the key.

    I've not had significant bother with "fake pixels" or "weird Bayer images"
    in my own photography, though.

    Cheers,
    David
     
    David J Taylor, May 1, 2010
  12. Bubba

    Guest Guest

    yes they do.

    that is not suitable for a still camera, and now video cameras too.
     
    Guest, May 1, 2010
  13. Bubba

    Guest Guest

    so does the human eye. chroma is 1/10th of luminance, so bayer actually
    has more than the eye can resolve. it's not a problem.
    there's more to it than just that.
    true, but sigma skips the aa filter entirely which is an even bigger
    problem.
     
    Guest, May 1, 2010
  14. Bubba

    Ray Fischer Guest

    No, it isn't. What's important is what you do with the light that you
    get. Eliminate all that glass and diaphram and camera body that
    blocks all that light, eliminate the color filters and all the space
    between sensels and you'd get a lot more of the light. And for a
    phometry experiment that'd be useful but you wouldn't get an image.
    In case you didn't know, professional video cameras have much, much
    lower resolution than even compact still cameras. Good thing, too,
    since aligning three high-resolution sensors would be difficult and
    very expensive and bulky and delicate.
    Your obsession with "losing light" is ... odd.
    Who cares? Stick a fast lens in front.
     
    Ray Fischer, May 1, 2010
  15. Bubba

    Guest Guest

    if someone is taking photos to be viewed by humans, then it *is* the
    reference.

    if you can't see it, then there's no need to capture it.
     
    Guest, May 2, 2010
  16. Bubba

    Martin Brown Guest

     
    Martin Brown, May 2, 2010
  17. Bubba

    Jeff R. Guest

    Haven't done much astrophotography, huh?

    One of the genuine attractions of photography in astronomy is revealing what
    the eye, with or without artificial magnification, cannot possibly see.

    Similar argument, though not as clear cut, for long telephoto and maybe even
    for photomicroscopy.

    ....but then, if I can't *see* the Horshead nebula, I guess there's no need
    to capture it.
     
    Jeff R., May 2, 2010
  18. []
    I find that low-light night-time shots sometimes look a much more
    realistic when converted to monochrome - it also avoids those nasty issues
    of mixed lighting sources....

    Cheers,
    David
     
    David J Taylor, May 2, 2010
  19. Bubba

    Guest Guest

    true, you don't, unless you are making *very* huge prints.

    for an 8x10" print @ 300 ppi (generally considered 'tack sharp'), you
    only need 7.2 megapixels.
     
    Guest, May 2, 2010
  20. Bubba

    Guest Guest

    that's a bit of a straw man. if you are going to be viewing the
    pictures 'at night', i.e., in dim lighting, you won't be able to see
    the colours so you don't need to capture them. use a b/w sensor and
    reduce the storage for the images.
     
    Guest, May 2, 2010
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