Possible to extract high resolution b/w from a raw file?

Discussion in 'Digital Photography' started by bob, May 10, 2011.

  1. bob

    bob Guest

    Is it possible to to extract a b/w photo from a camera raw file that is
    higher resolution than the color version, since one color pixel is made up
    of 4 b/w pixels with color filters?
    bob, May 10, 2011
    1. Advertisements

  2. bob

    Bruce Guest

    I often wonder why no manufacturer offers a b/w digital SLR or digital
    rangefinder camera (yes, Leica Camera, that's you!). I think it would
    be a strong seller to a niche market.

    In the meantime, I am very satisfied with ADOX CM 20 film, which
    probably has about the best resolving power of any currently available
    photographic medium:

    Bruce, May 10, 2011
    1. Advertisements

  3. It is not. It's made up of the pixel itself and then (with some
    intelligent processing) of the values of it's neighbours with
    different colours.

    Wolfgang Weisselberg, May 10, 2011
  4. bob

    ray Guest

    I'm not aware of any current software that does that. I'm not an expert
    either, but I do know a bit about digital signal processing. Seems to me
    that a different de-mosaicing algorithm would have the potential to do
    ray, May 10, 2011
  5. bob

    shiva das Guest

    Phase One makes a monochrome back for medium format cameras, "the
    Achromatic+ digital back", 39MP, which does not have a color filter.

    "The Phase One Achromatic+ is available for the Mamiya 645 AFD
    (including the Phase One 645DF camera), Contax 645 and Hasselblad V

    "Also available is the Phase One Achromatic+ for Hasselblad H1 and H2

    "The Achromatic+ can be ordered without an IR filter mounted
    permanently. There are multiple solutions available for working with
    interchangeable filters for such a solution."

    shiva das, May 10, 2011
  6. bob

    Guest Guest

    kodak had a couple and they weren't.

    it makes a lot more sense to use a standard sensor and convert to b/w
    when you want it, without giving up the ability to shoot colour when
    you don't. it's also substantially less expensive, since low volume
    sensors are not cheap.
    Guest, May 10, 2011
  7. bob

    Guest Guest

    it isn't, which you confirm.
    he gave no number, so it doesn't.
    actually, it's 5: the pixel itself plus the 4 direct neighbors (up,
    down, left, right). i don't know of anything that does that, since it
    looks like shit. normally 9 is considered the minimum.

    if you're thinking of a 2x2 block for a 4 pixel minimum, no. bayer does
    not work that way.
    true, which means that it doesn't use 4.

    typically it's 9 (good) or 25 (better) and occasionally even more but
    it begins to not be worth it at that point.
    actually, quite accurate.
    Guest, May 10, 2011
  8. bob

    Martin Brown Guest

    Actually he is right that a matrix of 4 cells is the bare minimum that
    can be used for Bayer demosaic although the results are not great.

    The pattern of 5 you describe fails completely for all red and blue
    sensor sites which in the standard Bayer mosaic have only green direct
    neighbours. At least Floyds method would allocate full RGB pixels to
    every location on the grid apart from at the very edges.


    Is the unit cell of the Bayer sensor grid.
    In a real sense it does sometimes although heuristics are used based on
    the green channel information to decide what weights to use. The default
    is 3x3 unless special conditions like sharp luminance edges are found.

    The detailed algorithms are patented but in rough form green channel is
    used to work out a crude green (proxy luminance) value for all the
    unsampled points and then a heuristic shader uses the red and blue
    pixels to fill in the gaps. Most digicams actually interpolate to a 2x1
    chroma subsampled image that will be JPEG encoded. There are only 2G 1B
    1R pixels per unit cell and it makes no sense to interpolate up to a
    full colour 4G 4B 4R then convert to 4Y 4Cr 4Cb and subsample when you
    can retain more accuracy and do it quicker from 4Y 2Cr 2Cb into JPEG.
    Typically it uses 9 and maybe a few from the next ring out to try and
    work out if there is a sharp edge transition and chose the right tweak.
    No it isn't. Each pixel location in the final image is potentially
    related to all its neighbouring sensor sites as well as its own measured
    value. Measured values are not normally allowed to change in Bayer
    demosaicing but may be altered by any unsharp masking done later.

    The individual pixel tells you one colour channel at that point in the
    image. The green channel is fairly informative and is used to generate
    the first guess at luminance and then the red and blue are combined in.

    The answer for the OP is that it depends. If you know the precise
    blurring function of your monochrome image and it obeys some very strict
    criteria then scientific deconvolution codes can be used to get a
    roughly 3x increase in resolution in regions of high signal to noise at
    the expense of various artefacts. The HST myopia problem was worked
    around using these codes and they were used to diagnose the fault but it
    isn't quick and the results are not always pretty. Unsharp masking is by
    comparison quick, crude but moderately effective.

    Martin Brown
    Martin Brown, May 10, 2011
  9. bob

    Guest Guest

    only if you accept shitty results. 5 is the minimum if you want to
    maintain the actual resolution of the sensor, not cut it by 75%.
    i definitely understand how it works.
    Guest, May 10, 2011
  10. bob

    Guest Guest

    right, the results are awful and also very low resolution. no bayer
    camera uses 2x2 blocks. it's stupid and a straw man.
    i wouldn't say fail completely. green is the main component of
    luminance (and in the original bayer patent, only green was
    considered). the colour errors will be high but the eye isn't that
    sensitive to that.

    a realistic minimum is 9 pixels. yes you 'can' do it with less but
    nobody does.
    nobody uses 2x2, except in the minds of some foveon fanbois thinking
    that's how bayer works (it doesn't).
    Guest, May 10, 2011
  11. bob

    Bruce Guest

    The risk of moire is hugely overstated. I shoot with a 14 MP Kodak
    DCS Pro 14n full frame DSLR and a 39 MP Hasselblad. Both have Kodak
    sensors with no AA filters. Moire isn't a significant problem for me.
    I can think of a lot of systematic flaws in images that occur much
    more frequently than moire. Moire is something that troubles armchair
    "experts" far more than it troubles working photographers.

    If moire really was a problem, everyone would be using AA filters all
    the time. The reality is that the sharpness of images rendered
    without AA filters is very attractive, especially among fashion
    photographers. Yet fashion is the genre most likely to have problems
    with moire because of woven fabrics! Go figure ...

    P.S. It is also worth pointing out that Nikon (and some other
    manufacturers) have installed weaker AA filters with each new
    generation of their digital SLRs. The result is that Nikon's sensors
    now significantly outperform Canon's in terms of image sharpness
    before post-processing is applied.

    Nevertheless my 14 MP Kodak 14n (from 2004!) still outperforms my
    Nikon D3 by a worthwhile margin at base ISO. It should probably be in
    a museum, and has many flaws, but the image quality still takes my
    breath away. Dynamic range is very good indeed and the natural colour
    rendition is better than that of any other DSLR I have used. It's a
    pity Kodak didn't develop it further. The 39 MP Kodak sensor in the
    Hasselblad is also excellent - and that's another camera that's far
    from being the latest model!
    Bruce, May 10, 2011
  12. bob

    Guest Guest

    the 'italian flag syndrome' is very common with the kodak slrs.
    and in fact, they are. almost every digital camera has an antialias
    filter, the main exception being sigma.
    attractive to some, ugly to others.
    actually nikon's aa filters have been getting stronger. the d70 was
    weak and exhibited colour fringing and recent cameras are noticeably
    stronger to minimize that.
    for other reasons.
    bullshit. it's not even in the same league. the 14n had a very noisy
    sensor and topped out at iso 400. it also had a 12 bit a/d converter so
    it *can't* outperform the d3.
    it is not wider than a nikon d3 or a fuji s5, or most modern dslrs. it
    was actually not very good.
    Guest, May 11, 2011
  13. bob

    Bruce Guest

    That back has been advertised for some time but in spite of knowing
    quite a few digital medium format shooters I don't know anyone who has
    bought one. None of the top three PhaseOne resellers in the UK has
    one available.

    The use of interchangeable digital backs is rapidly dying out in any
    case, as is their use on medium format film SLRs. The trend is
    strongly towards integrated medium format DSLRs with Hasselblad having
    the majority of the market, at least here in Europe.

    I would be keen to try a monochrome sensor but my Hassy is an H3 and
    won't take an interchangeable back.

    I get the impression that the Achromatic+ has perhaps been left
    Bruce, May 11, 2011
  14. bob

    Guest Guest

    yes really.
    good luck if your subject moves. how many of those do you see in a
    camera store? zero. can you say irrelevant?
    Guest, May 11, 2011
  15. bob

    Bruce Guest

    I'm sorry to have to tell you that my Kodak DCS Pro 14n has a CMOS
    sensor, and that Kodak CCD sales to manufacturers such as Pentax,
    Hasselblad and Leica are thriving! ;-)

    But thank you for making me smile. I've just finished shooting a
    corporate event at London's South Bank. I'm tired and even more
    irritable than usual, and I'm having to wait until proofs of every
    shot taken are printed off, approved by the client and handed over.

    It's been a long night and at 12.32 AM it is still far from over! :-(
    Bruce, May 11, 2011
  16. bob

    Martin Brown Guest

    The resolution is the same as the original sensor. You can always select
    a boxcar of 4x4 sensor sites comprising GRBG in some permutation.
    Fail completely in that half your reconstructed pixels are completely
    missing any blue or red channel information. You don't understand what
    you are talking about.

    The colour fringing of diagonal sharp luminance transitions on Bayer are
    awful if you do not handle them correctly. And the correct solution is
    approximately to choose the most appropriate self consistent 4x4 pixel
    block based on the crude estimated luminance values.
    The practical implementations all use (at least) the 9x9 block centred
    on the home cell but they can and do select different subset strategies
    to avoid bleeding spurious colour into sharp white to black transitions.

    Martin Brown
    Martin Brown, May 11, 2011
  17. "bob"s description --- and your agreement --- can be read as "for
    every 4 bayer sensors, there is one resulting colour pixel, i.e. a
    10 MPix resulting image needs 40 million bayer sensor cells".
    Which, as you know, is untrue.

    Nope. Difference between "neighbours" and "made up of".
    Difference between "4" and "neighbours".
    3. One red, one blue, one green.
    What I said.

    Wolfgang Weisselberg, May 11, 2011
  18. bob

    Guest Guest

    unless you have a rotating platform that syncs with the earth, they do,
    and what if you want to take pictures of other stuff?
    Guest, May 12, 2011
  19. bob

    Bruce Guest

    Kodak made the DCS Pro 760m b/w DSLR which was based on the Nikon F5
    and had a 6 MP CCD. Two pro shooters told me that the 760m never
    seemed to be available, and they don't know of anyone who actually
    managed to buy one. For some of the reasons why, read this review of
    the DCS 760m on the Luminous Landscape web site:


    There was apparently going to be a b/w version of either the 14 MP
    Kodak DCS Pro 14n or later SLR/n, but it never appeared.
    Bruce, May 12, 2011
  20. bob

    RichA Guest

    The sensors in those camera are to the ones in the Hasselblad as the
    D3 image is to a D40, one's a pro image, the other sports cartoon
    colours designed to please soccer moms. Everything in the Hasselblad
    back is higher grade, including the sensor, when it comes to critical
    accuracy of things like colour. That is why Kodak (and Dalsa) sensors
    dominate the science fields while Canon and Sony are no where to be
    seen except in the least-demanding applications, like surveillance and
    other related work.
    RichA, May 12, 2011
    1. Advertisements

Ask a Question

Want to reply to this thread or ask your own question?

You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.