Steps From Levels?

Discussion in 'Digital SLR' started by Wilba, Aug 16, 2009.

  1. Wilba

    Wilba Guest

    Insubordination can only exist within an authoritative relationship. I find
    it strange that you think I have the right to tell you what to do. :- )
    You don't have the right to tell me what to do either. :- )
    If you try it I expect that unless you have a very different camera and
    monitor to mine, you'll found it quite unsatisfactory.
    I first came across the logically correct nomenclature in the early '80s, in
    a long-forgotten photography book.

    Without actually explaining how "stop" came to be associated with apertures,
    this article - - complies with
    the principle expressed in its footnote, "In optics, the term "stop"
    properly refers to the aperture itself, while the term "step" refers to a
    division of the exposure scale. Some authors, e.g., Davis (1993, 13), prefer
    the term "stop" because they refer to steps (e.g., on a step tablet) that
    are other than powers of 2. ISO standards generally use "step", while
    photographers normally use "stop"."

    Other instances? "Within any exposure factor (Exposure Value, film speed,
    aperture, shutter speed) each step is double (or half of) the preceding
    step." (

    On the origin of "stop" - "The term ['one stop'] most directly relates to
    aperture. It goes back to the time when cameras were first equipped for
    control of aperture. Commonly, a metal plate carrying a number of holes of
    different diameter passed through a transverse slot in the lens barrel. It
    was said to "stop down" the lens aperture, and the different holes were said
    to be "stops". The photographer moved the plate to put into place the
    appropriate stop for a particular exposure. Commonly, successive holes had
    areas that differed by 2:1. Thus a 2:1 change in aperture area came to be
    known as a "one stop" change."

    To argue your position, you'd have to explain how expressions like "stop
    down the shutter" (as an action), or "ISO stop" (as a noun phrase), make
    literal sense. And to anticipate your retort, the repeated misuse of a
    technical term to represent something else doesn't make that usage correct.
    "... measure or determine the number of exposure steps [zones] ...". There's
    nothing in my question or the subsequent discussion that says "number" has
    to be more precise than one significant digit. You're arguing against your
    own unfounded assumptions and prejudices.
    The image on the monitor is the final representation.
    Eight steps.
    Wilba, Sep 5, 2009
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  2. I don't think so, but you quite behaved like it was the case.
    If English isn't your first language, you are excused from not
    noticing any differences between "you should", "you must" and
    "do it or else". :->
    It works well enough.
    It also shows the monitor doesn't produce 8 an stop range between
    0,0,0 and 255,255,255. Yes, calibrated monitor. Wheee --- out
    of the window goes your assumption. As I said, your calculations
    and musings depend too much on unwarranted, unchecked assumptions.
    Nomenclature is rarely logical, since it usually grows with the
    field it describes. Unless it's invented more or less
    completely at the start ... no chance.

    I don't know if you are a photographer, but I am virtually
    certain you are no ISO standard.
    Nope, I don't have to. I will just point out that my camera
    allows me the choice to change shutter and exposure in half and
    third stop steps, each step being thus very different from a stop.

    How does your nomenclature handle steps that are smaller than
    steps? Does 1/3rd step steps sound logical, useful or (and
    that's what nomenclature is needed for) unambigous?
    As in ... "your monitor has quite exactly 8 stops range"? Yes, I took your
    word somehow, won't happen again.

    And how comes you want ONE significant digit and just dividing
    the range of 0-255 in 8 equilong steps doesn't do it for you?
    *Obviously* you wanted more ...
    So please take your camera and measure 0,0,0 and 255,255,255.
    What's aperture, exposure time, ISO setting? Roughly is good
    enough for a basic check.
    And what size are these steps?

    Wolfgang Weisselberg, Sep 5, 2009
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  3. Wilba

    Wilba Guest

    Not my assumptions. Not my calculations. Not relevant to the topic. So your
    gripe is with Koren. No worries. I'll leave it with you and him (see
    LOL. Nice try! (Irony.)
    If precision was required, I'd use the same term for that thing in that
    context as does my camera's menu system - "exposure level increments" -
    unless a more apt generic term was accepted by consensus.

    Returning to the subject of this fibre, it remains for you to prove that
    "stop" is right and "step" is wrong as a shorthand for a power-of-2 exposure
    value step not specific to variation by aperture size.
    Wilba, Sep 6, 2009
  4. I did ask you. You asserted that your monitor had 8 stops ...
    based on something you read somewhere.
    Right, you copied them.
    Your assumtions and the calculations you pulled up are "not
    relevant to the topic"? Well, well, well.
    Nope. My gripe is with you, not with someone you quoted
    without understanding.
    Ah, you have no answer.
    You're perfectly right, "exposure level increments ... 1/3rd
    stop" is what my camera calls it. Inclusive calling it st*o*p.
    Just like your camera. :) Want a screen shot?.

    You just replaced the wrong 'step'! Duh, but I admit, it's an
    easy mistake. Another reason to use stops.
    Yes, have you measured the contrast range of yon screen yet?
    So what's the answer, how did you measure it and under which
    conditions (daylight and incandescent light and full darkness
    would be a start) did you do it?
    I'm not saying that step is absolutely wrong, but at least uncommon
    useage for what you use it for and prone to misunderstandings.
    My monitor has a range of as many steps as the graphic adapter
    outputs (it's an analog device, see?) and a certain range of stops
    that mostly depend on how black black is (see reflected light).

    Wolfgang Weisselberg, Sep 6, 2009
  5. Wilba

    Wilba Guest

    Everything you've said is attacking your own fantasy, created by twisting
    the question and my answers to suit your goals.

    (For the last time) it's nothing to do with how the eye sees the scene or
    the image. It's only about the levels in the image data (as shown, for
    instance, by the Info window in Photoshop).

    Any claim that you subsequently make that I _intended_ a different question
    is hereby pre-invalidated. :- )
    Yon screen in front of me? Yes I have, and the result was interesting, but
    irrelevant as ever.
    Right, so we agree that it's wrong to make assertions like, "it's not
    st*e*ps, it's st*o*ps". Thanks.

    Thanks for helping me make sense of this for myself. It has been fun. I will
    only reply to you if you say something relevant about the actual question.
    Wilba, Sep 8, 2009
  6. I apologise. I was mistakenly thinking you were talking
    about photography or visual arts. You know, the stuff you
    need to use your eyes for.

    What you _wanted_ all along but never said was:
    | If I *randomly*[1] decide that a field of RGB-data *has* 8 stops
    | of luminance contrast between 0,0,0 amd 255,255,255 and if said
    | field was gamma-2.2 8-bit encoded, what would *roughly* be the
    | step size for one stop of difference?
    | [1] on no factual basis, just based on something I read and didn't
    | test nor understand for monitors.
    What you _wrote_ was something completely different:
    | If I'm looking at an image in something like Photoshop (in which I can
    | easily read the RGB levels for any pixel), how can I measure or determine
    | the number of exposure steps between two pixels or areas in the image?
    (see Message-ID <02977b2a$0$20630$>)

    - without stating that you have decided on 8 stops
    - without talking about 'roughly' --- misleadingly giving the
    opposite idea you needed quite exact answers
    - without making clear that your "exposure steps" were not
    meant as 1/3 or 1/2 stops ...
    - while misleadingly claiming you were looking at "an image"
    --- it's not an image, it's a field of data to you, and you
    don't look at it, you measure RGB levels

    Thus you may have not intended a different question, but you sure
    *wrote* a completely different question. Hence I must question
    your question-writing ability. Questions?
    Exactly as I thought, it's not even within one stop of 8 stops,
    for else you'd given me the rasberry and danced "it's 8.2 stops,

    So we agree that st*e*ps is the wrong word to use. Thanks.

    Wolfgang Weisselberg, Sep 8, 2009
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