The Implications of the "Number of Bits" of DSLRs

Discussion in 'Digital Photography' started by RiceHigh, Dec 12, 2006.

  1. RiceHigh

    RiceHigh Guest

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  2. You have a lot of misconceptions in your article, some
    propogated from Reichmann.

    # bits actually needed is dependent on the sensor,
    and the smaller sensors coming out today do not necessarily
    need more than 12 bits; some even less.

    The digital transfer curve reduces the need for as many
    bits (this is a variable gamma encoding scheme).
    Regardless of some perceptions, more bits are NOT needed
    in the top cameras for the high end, as photon noise
    becomes greater than 1 digital number above a few dozen
    photons (which is most of all images).

    You have many incorrect statements, such as:

    "So, how important is this "number of bits" figure
    on the image quality and the tonal response
    (smoothness in transition, etc.)? It is very
    trivial that the more levels it records, the
    smoother the tonal quality and response it would be."
    -- No, photon noise limiting.

    "However, it is the main weakness of *any* digital
    camera that the number of tonal levels at the shadow
    areas are much less than those counted at the
    brighter parts, i.e. the highlights, owing to
    the primitive nature of CCD/CMOS imager"
    -- incorrect. The sensors are linear, and the
    tone curve compresses tonality in the high end, not the
    low end. See Figure 7 at:
    Dynamic Range and Transfer Functions of Digital Images
    and Comparison to Film

    "As such, assuming *perfectly* ideal exposure which
    means that an evenly spread histogram is obtained,..."
    -- Incorrect. There are many correctly
    exposed scenes where histograms are not "perfectly spread."

    "Well, at this point, what I must emphasize (again,
    as always) is that an accurate metering and exposure
    system of the DSLR is of prime importance than anything
    else, given that the number of bits of the RAW file
    is the identical."
    -- doesn't make sense.

    "So, in the end, you need a high bit *output*
    device to output your high bit pictures, if any."
    -- Incorrect. You need good processing to
    compress the range for the output device.

    "Last but not least, if you still have some
    unresolved puzzles about the basic concept(s)
    in your mind after reading all these here..."
    -- This describes your article.

    #bits needed depends on the sensor performance. Much
    of what we are seeing today is marketing hype.

    Some references related to your article:

    Digital Camera Sensor Performance Summary

    Digital Camera Raw Converter Shadow Detail and
    Image Editor Limitations:
    Factors in Getting Shadow Detail in Images

    Digital Camera Raw versus Jpeg Conversion Losses

    Digital Imaging Information

    Roger N. Clark (change username to rnclark), Dec 12, 2006
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  3. RiceHigh

    John Turco Guest


    Hello, Roger:

    Furthermore, "*perfectly* ideal exposure" is painfully redundant. <g>

    John Turco <>
    John Turco, Dec 15, 2006
  4. RiceHigh

    ASAAR Guest

    Ouch! . . . and moresofurthermore, one can only wonder why it
    has taken so long for Roger N. Clark and RiceHigh to produce such a
    *perfectly* ideal pairing, the likes of which hasn't been seen since
    Roger met Ilya, Harry met Sally and Bob, Carol, Ted and Alice met.
    ASAAR, Dec 15, 2006
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