maximum dynamic range using RAW

Discussion in 'Digital Photography' started by Frank van der Pol, Dec 21, 2003.

  1. Agreed - it sounds as if 10-bits is not enough under certain
    circumstances, although this also depends on the amount of noise coming
    from the CCD and electronics. There is no point in making the ADC have
    _too_ many levels! The actual valus would be very camera specific, of

    David J Taylor, Dec 22, 2003
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  2. Frank van der Pol

    JPS Guest

    In message <>,

    Your feeling is correct.
    It depends on the camera, really. The Canon 10D's extra dynamic range
    in the RAW file (above what becomes 255 in a JPEG with normal contrast)
    is 0.9 stops for blue, 1 stop for green, and 1.6 stops for red. This
    means that light that is mostly red actually fits well into its dynamic
    range. It is actually daylight and flash that are less efficient in the
    10D, not tungsten. In fact, if you're shooting under tungsten light
    without a filter, you might want to boost the exposure a little, or if
    you don't have enough light to do that, go to the next higher ISO and
    compensate exposure +1, to take maximum advantage.
    Put a grey card next to the light source, so that a gradient of
    intensity forms across it. Then, photograph the grey card, exposing so
    that the brightest parts are about 4 stops brighter than neutral grey.
    Then, using a RAW converter, see how much you can force under-exposure
    in each channel before you rescue it from the clipping point.
    If you're really curious and want to know how to take best advantage of
    your equipment, you should try to reverse-engineer it, and not assume
    that it has the same limits or sensitivity to each color. I know much
    more about my 10D than Canon would ever tell me in a manual, by
    conducting experiments.
    JPS, Dec 25, 2003
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  3. Frank van der Pol

    JPS Guest

    In message <>,
    He wants maximum dynamic range for all colors. Of course, that would
    require special lighting, or special filters for some kinds of light.
    JPS, Dec 25, 2003
  4. Frank van der Pol

    JPS Guest

    In message <v%CFb.3499$7%>,
    There's no such thing as "correct exposure" with digital RAW files.
    This is not film, where you have the grain just below, and a soft
    shoulder above, with no contrast. The sensors are generally totally
    linear, and a stop is 0.5x or 2x the voltage, exactly. If you expose
    too much, you clip one or more channels. If you just barely avoid
    clipping, you have maximum dynamic range in your image, and a higher S/N
    ratio. In a picture of a grey card, optimum exposure would be the
    "wrong" exposure; it would be about +3 EV, and you'd use the same thing
    for an optimum white card, and an optimum black card! The optimum
    exposure for digitals is always the highest that manages to avoid
    clipping. Each color channel has a different amount of highlight
    headroom, and the optimum exposure may be with a light that is not
    white! With my Canon 10D, optimum exposure of a grey object occurs when
    green light is 0.1 stops higher than the blue, and the red is 0.7 stops
    higher than the blue.
    JPS, Dec 25, 2003
  5. Frank van der Pol

    Robertwgross Guest

    Excellent. Your Canon 10D does not even have a CCD sensor!

    ---Bob Gross---
    Robertwgross, Dec 25, 2003
  6. Frank van der Pol

    JPS Guest

    In message <>,
    Are you aware that 255 is not the ceiling in a RAW file, at least in
    some cameras.

    The white that the Canon 10D would render as 255,255,255 in a JPEG of
    normal contrast is not the ceiling in a RAW file. The highest RGB value
    (on a scale of 0 to 255, with 128 as 18% grey) for this camera is about
    424,351,340, but everything over 255 will be clipped to 255 if you do
    not use a RAW converter that properly "pulls" or under-exposes for you
    (the Canon converter is broken in this regard).
    JPS, Dec 25, 2003
  7. Frank van der Pol

    JPS Guest

    In message <>,
    Some cameras, like the 10D, have the most headroom in the red channel.
    The camera isn't intelligent enough, however, to boost exposure when
    using a reddish light source. You can get less noise in the blue
    channel by simply using a positive exposure compensation. If that robs
    you of shutter speed or DOF, you can always go to the next higher ISO
    and shooting at +1 EC, which has the same S/N ratio, but more bit depth,
    making it easier to "see through the noise". Of course, at ISO 1600 and
    3200, the 10D is actually shooting at ISO 800 and 1600, respectively,
    with an EC of -1 (beyond what the user sets) and doubling the RAW
    numbers during the A2D conversion, so that must be kept in mind.
    JPS, Dec 25, 2003
  8. Frank van der Pol

    JPS Guest

    In message <>,
    16-bit mode doesn't give you more headroom; it gives you more precision.
    Unless, of course, you take advantage of PSCS' new 16-bit layers, and
    use a smaller range on your working edit and use an adjustment layer to
    bring it back to scale.
    JPS, Dec 25, 2003
  9. So much light there I would have thought dynamic range ceased to be an
    I was simply distinguishing between "poor" light and "good" light

    I accept your point that the exposure will be a compromise because of
    specular highlights.

    David J Taylor, Dec 25, 2003
  10. schreef in bericht
    Yes I am. I already discussed that in the other part of this thread
    with David Taylor.
    Could be. Probably is. I don't know. I use a Fuji S2 and I think its
    RAW converter does a very good job. My aim was more or less to make
    use of the whole dynamic range in each of the channels in the RAW file
    in order to optimize the dynamic range.

    Frank van der Pol, Dec 25, 2003
  11. schreef in bericht

    The Fuji RAW converter can actually get that extra stop headroom back
    into th 0-255 scale, but even then, the last last bit of headroom can
    be found in the red channel. It could therefore be worthwhile e.g. to
    use a tungsten conversion filter when you are working with flash (or
    outdoors) in RAW mode.
    ....and of course with a white and gray kept neutral in the resulting
    ..tif image.

    Thanks for the suggestion. I'll try this and I'll see what it will

    Frank van der Pol, Dec 25, 2003
  12. Frank van der Pol

    Jeremy Nixon Guest

    How do you determine that (for a particular camera model)?
    Jeremy Nixon, Dec 27, 2003
  13. Frank van der Pol

    JPS Guest

    In message <>,
    Overexpose a picture of something white wih a grade of tones, and
    underexpose it in a RAW converter, like Capture One. With the 10D, you
    can underexpose the red channel by 1.6 stops and still have detail
    differences between 254 and 255 in the output. Unfortunately, most RAW
    converters will only use this extra red detail for color balancing, and
    will render everything greyscale above the level where the blue runs
    JPS, Dec 27, 2003
  14. Frank van der Pol

    Chris Brown Guest

    This extra red headroom has saved my bacon recently in night shots of a city
    where there was an interesting building in the background, floodlit by
    sodium light. The red channel was blown in the original histogram, but once
    I took the white point, the surface detail became visible again. Very handy.
    Chris Brown, Dec 27, 2003
  15. Frank van der Pol

    JPS Guest

    In message <>,
    The things they don't tell you in the manual!
    JPS, Dec 27, 2003
  16. Frank van der Pol

    Lionel Guest

    Kibo informs me that stated that:
    Yes, you're quite correct. I phrased my comment poorly.
    I haven't had a chance to experiment with those features, unfortunately,
    but I'm looking forward to it. :)
    Lionel, Jan 2, 2004
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