Bayer filter removal

Discussion in 'Digital Photography' started by David Dyer-Bennet, Apr 13, 2007.

  1. Is any company offering removal of the Bayer filter from a Nikon-mount
    DSLR? Particularly the D40? (I suspect it may not be feasible due to
    the stacking order and how the microlenses, AA, IR cut, and Bayer are
    combined, and other issues, and I haven't been able to Google up much,
    but I thought asking might still turn something up.) I'm interested in
    a high-sensitivity B&W camera for low-light situations.
    David Dyer-Bennet, Apr 13, 2007
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  2. Interesting idea. Would one necessarily lose the micro-lenses as well and
    would that mitigate against removal? I don't really know, by the way. Here
    is an interesting link that might be helpful:
    Charles Schuler, Apr 13, 2007
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  3. Interesting, and had some detail I didn't know, thanks!

    Doesn't mention where the IR-block filter is in all that, either, or the
    optical anti-aliasing filter. I suspect it varies considerably.

    I suspect that the microlenses would be a major loss; but I suppose
    trying it with various lenses would be interesting. The worst
    complaints are about ultra-wide lenses, and I don't use them in the
    conditions I want this camera for. (I'm not *at all* sure that I'm
    prepared (mostly financially) to be the first experimenter here :)).
    David Dyer-Bennet, Apr 13, 2007
  4. The stacking technology of the various filters is an interesting issue. The
    IR filter must be near the top, at least in some cases, since one can find
    sources such as this one:

    Now that digital cameras are enjoying rather brisk sales, I wonder if
    specialized models are near. Canon's astral model is but one indicator:

    You want a B&W camera with the best possible sensitivity, and you are not
    alone. I'd guess it is coming soon.
    Charles Schuler, Apr 13, 2007
  5. David Dyer-Bennet

    cgiorgio Guest

    Certainly nobody will do that, Also you could easily buy a couple of D1 MK 3
    's plus assorted lenses for the cost of doing that. It would be a more
    realistic approach to cool the sensor with liquid nitrogen (and float the
    camera with dry nitrogen to keep water out) to achieve a higher signal /
    noise ratio. A full frame sensor camera or a larger than full frame camera
    (like Mamyia) would be the easiest solution for achieving improved signal to
    noise ratio.

    In production multiple sensors are processed on a wafer (4", 6" or 200 mm)
    and only separated after they have run through all the processing steps
    (except for bonding).

    Even if a pin compatible black and white version of the original sensor
    would exist, it would need custom developed image processing (ASIC's and
    firmware) because processing black and white pixels can not use the same
    weighting used as for processing the signals from a Bayer matrix sensor.
    Recording in RAW and using a customized external converter program to obtain
    an image from that would be slightly easier - but probably not for any *.nef
    files, as these are not true RAW but store pre processed data. The camera
    display would also be pretty useless, but I did not have that on my film
    cameras and could still take pictures.
    cgiorgio, Apr 13, 2007
  6. David Dyer-Bennet

    Nervous Nick Guest

    That is a *really* informative link, Charles. Thanks, man. It is
    pretty technical, but goddam thorough.
    Nervous Nick, Apr 13, 2007
  7. I can't tell if you know more than me on this topic, or less. I don't
    believe that the Bayer filter is fabricated directly on the sensor as
    part of the manufacturing process in most cases, but I don't have a good
    specific source to point to, either.

    I do know that a number of places offer cameras with the IR-block
    filters removed, and there are instructions floating around for how to
    do that yourself in various models. The cost for the commercial
    versions is modest.
    I very much doubt that LN cooling is feasible today for a camera I could
    use to take photos at dimly-lit music parties.

    A larger-sensor camera would have lower noise, but it would use much
    slower lenses; this is why photojournalism and especially street
    photography migrated to 35mm in the first place.
    Digital IR photos are frequently taken by using a visible-light-blocking
    filter. This greatly reduces the sensitivity, but usable IR photos can
    be taken with most digital cameras this way. I believe the dyes in the
    Bayer filter are mostly transparent in the infrared (or at least all the
    colors are about the same density in the infrared). With P&S cameras,
    the preview is reasonably accurate, and looks mostly monochrome, as does
    the captured image. So I'm not at all sure that a rework of the
    firmware (or external processing using a true raw file) would be
    necessary to achieve usable B&W results. (I've shot infrared with an
    Epson 850Z and a Fuji S2 using the Hoya r72 visible-light-blocking
    filter). (A rework of the firmware or external RAW processing with a
    special B&W version of the software might give some real increase in
    resolution, though.)
    David Dyer-Bennet, Apr 13, 2007
  8. David Dyer-Bennet

    John Sheehy Guest

    All a firmware or hardware needs to do is use a certain WB setting to
    display the grey RAW data as grey RGB on the LCD, or in the JPEGs, and bias
    the metering. The only artifacts might be slight color fringing in high-
    frequency high-contrast content, when zoomed in sufficiently. If the
    camera already has B&W mode (intended for the CFA), that won't even happen.

    John Sheehy, Apr 14, 2007
  9. Unlikely. Although I've not looked into the Sony APS-C sensors, their P&S
    sensors build both the microlenses and color filters into the chip. Since
    even the slightest registration error would be a complete disaster, it's
    unlikely that the color filters are any different on the APS-C sensors.
    Since the color filters are largely transparent to IR, the best you get is a
    reasonably sensitive IR camera by removing the IR cut filter (and maybe the
    low-pass filter).

    High on my wish list is a dSLR with interchangeable sensors. It should be
    possible. A 5DII with both a 16MP color sensor and an 8MP B&W sensor would
    be seriously neat. I'd certainly cough up between US$700 and US$1000 for the
    8MP sensor.

    David J. Littleboy
    Tokyo, Japan
    David J. Littleboy, Apr 14, 2007
  10. And that's the answer I'm getting from people who actually perform
    conversions, too. I'm not surprised; but I was hoping my vague ideas
    were *wrong*. Oh well.
    That has its own temptations, but completely different ones. And not so
    tempting for me (though I've done IR a little with my last two digicams).
    Something like that would be really nice.
    David Dyer-Bennet, Apr 14, 2007
  11. David Dyer-Bennet

    Bill Funk Guest

    Since the processing done in-camera assumes the Bayer filter is there,
    wouldn't removing it (if it were possible) seriously farkle the
    I suppose if you shot in RAW only, the RAW file wouldn't be farkled,
    but how would you then process the RAW file, as all processing
    software assumes the presence of a Bayer filter?


    The White House admitted on Wednesday that
    e-mails about official business in Karl Rove's
    office were erased. The deleted e-mails were
    sent on Republican Party accounts instead of
    White House accounts to avoid a law that
    requires preservation of government records.
    It doesn't clog up the landfills like Hillary's
    shredder did for eight years.
    Bill Funk, Apr 14, 2007
  12. Not really; if you present a camera with a B&W scene it will render it
    in B&W, not fake colors. And if you present it with an infrared scene
    (with a visible light block) you'll get pretty much a monochrome
    rendering, even if the camera is set in a "color" mode (and of course
    most of them can be set for B&W anyway).
    Well, I have seen a specialized RAW processor mentioned for infrared
    shots that uses all the pixels (the Bayer filter cells are transparent
    in the infrared). And if necessary one can be written (I'm a software
    developer professionally; so while I'd prefer to avoid that level of
    involvement, if that were the *only* block, I'd take it on).
    David Dyer-Bennet, Apr 14, 2007
  13. David Dyer-Bennet

    Bill Funk Guest

    It still seems that removing the Bayer filter and shooting a color
    scene will seriously confuse the software; for example, without the
    filter in place, how will it know how to represent green? (RGBG
    putting twice as much green data into the system)
    Yes, the system will render B&W scenes properly, but what about color
    Well, sure, if you can do it, that's fine.
    However, for general (or even *limited* general) use, that's
    impractical; the distributed software model (free or paid) would be

    Plus, as you point out, the camera can be set to B&W output already,
    and it can also be done in post.
    There was another recent thread (here, I think) about converting a
    current DSLR into a B&W DSLR with a sensor of fewer MPs. My thoughts
    are the same as here: why? It can be done now, and the converted
    camera would be more expensive, and less functional.
    "Please, Mr. camera maker, make a camera that does less and costs
    I don't see it.


    The White House admitted on Wednesday that
    e-mails about official business in Karl Rove's
    office were erased. The deleted e-mails were
    sent on Republican Party accounts instead of
    White House accounts to avoid a law that
    requires preservation of government records.
    It doesn't clog up the landfills like Hillary's
    shredder did for eight years.
    Bill Funk, Apr 15, 2007
  14. Shooting infrared the simple way (visible-blocking filter over the lens,
    no camera mods) is presenting essentially the same signal to the
    sensor that removal of the Bayer filter would; it sees roughly equal
    values. And that works fine in many, many cameras.
    Well, if I took the trouble, I'd distribute it.
    The one I want does more -- it's 1.5 stops more sensitive and of
    significantly higher resolution with the same pixel pitch.
    David Dyer-Bennet, Apr 15, 2007
  15. Hi,

    Removal of the Bayer filter would give a lot more light throughput
    than 1.5 stops. You have not only the transmission of the
    filters but their bandwidths too as factors. If you removed the IR filter
    too, I think I computed once that you would gain about 50x in speed!
    Removal of the blur filter would also make very sharp B&W images.

    Some programs, like dcraw or imagesplus allow you to extract
    the raw data with no Bayer interpolation, so software exists
    to get the data out and into a proper form to take advantage
    of the system.

    There are companies that remove the IR filter (Heutech (sp?) for one),
    but removing the Bayer filters would require removal from the
    surface of the sensor, and I don't know anyone who does that.

    I would buy a 20D class black and white camera if such were
    to come on the market.

    Roger N. Clark (change username to rnclark), Apr 16, 2007
  16. Two of the places that do IR removal have confirmed the general
    impression that removing the Bayer filter isn't practical on current
    cameras. I'm not terribly surprised, but I figured getting more
    information than just my own impressions was worth the trouble of asking.
    I'd be extremely tempted, at least if it really had a stop or two more
    sensitivity (or more; more is always okay). Although for me it'd have
    to be a Nikon mount, or else I'd have to find enough money to replace
    bunches of lenses (some of which can't really be replaced in the Canon
    world). I was figuring that a D40 plus $300 conversion plus $150
    KatzEye screen (including installation) was something I'd have to find
    money for if the conversion were possible.
    David Dyer-Bennet, Apr 16, 2007
  17. Hmm. At first glance, that 50x seems way over the top, but if the filters
    actually attenuate in the pass band as well, a factor of 4x (assuming that
    the pass band is 1/4 of the band from IR to near UV) plus another 2 for the
    in-band attenuation, and that's a factor of 8x. So three stops is possible.
    It sounds like you are thinking of shooting under dim incandescent lights
    where there's a lot of IR and not much blue and green.

    I had originally thought that you'd only get a stop or so going to B&W, but
    if you think about the far higher QE of digital than film, it makes sense
    that seriously high sensitivities should be possible.

    One problem may be that lenses that can focus both IR and visible at the
    same time are few and far between...
    I'd leave the low-pass filter on. At least on the 5D, it's way too weak
    already, and probably just about right for 12.5MP B&W.
    At least on the P&S sensors, the Bayer CFA filters are below the
    microlenses, and both are fabricated on the chip.
    I'd rather a (16+MP) 5DII with interchangeable sensors and special-order
    options with and without the IR cut filters and with and without the
    low-pass filter so everyone can get the combination they want. I bet Canon
    would make a fortune on the color + no LPF combination. (The availability of
    this latter combination would bankrupt Foveon<g>.)

    David J. Littleboy

    Tokyo, Japan
    David J. Littleboy, Apr 16, 2007
  18. David Dyer-Bennet

    ASAAR Guest

    At first glance I agree with your first glance opinion. :)
    Charles Schuler posted an informative link in this thread a couple
    of days ago that may clarify the amount of attenuation that takes
    place if the Bayer Filter Transmission vs. Quantum Efficiency chart
    (Figure 4) is a fair representation. It shows fairly broad filters
    with a good deal of overlap, and quantum efficiencies at different
    frequencies ranging from about 8% to 38%, maybe averaging a little
    bit more than 20%.
    ASAAR, Apr 16, 2007
  19. David Dyer-Bennet

    Martin Brown Guest

    Would you not be better off with a faster IS lens?

    It might be possible to bleach the filters by exposing the chip to
    strong UV light with some risk of sensor damage increasing the noise.
    Or for certain camera combinations there are pin compatible monochrome
    only sensors. Consumer grade astronomical cameras tend to use them for
    semi serious science work (as opposed to single shot colour). However,
    even though they are excellent in low light they lag behind state of
    the art MP rankings by using larger area pixels.

    I doubt you will find a consumer SLR that permits swapping the sensort
    chip, but I could be wrong.

    Martin Brown
    Martin Brown, Apr 16, 2007
  20. [A complimentary Cc of this posting was sent to
    If you mean

    I do not see any QE spectral data on Figure 4. So what do you mean?

    To find the effect of removing of Bayer, one needs to average these
    curves with the coefficient given by the QE curve (well, it must take
    into account the IR filter too). In principle, one could try to guess
    the QE curve by dividing the "throughput" measured QE of
    IRF+Bayer+Sensor by the data for the Bayer.

    [Do not have the link for the measured QE at hand, but it was you who
    gave it to me. ;-]

    Hope this helps,

    P.S. Let me reiterate that my estimates of "throughput" QE of a 2005's
    Canon's sensor (with sunlit scenes) were about 14%.
    Ilya Zakharevich, Apr 16, 2007
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