experts help ISO vs EV+

Discussion in 'Digital Photography' started by Faiser, Nov 20, 2004.

  1. Faiser

    Faiser Guest

    All,

    I recently had an argument with a friend who claims that increasing the iso
    setting does in fact the exact same thing as compensating the exposure in
    post processing, but then inside the camera. According to him, manipulating
    the levels after exposure would give the same result.
    My idea is that on higher iso settings the sensor is more sensitive to light
    which is not the same thing as achieving this in post processing.
    Which of us is closer to the truth?

    Reason for our little argument was another C vs N discussion, where the iso
    100 of the C is supposed to be less noisy than the iso 200 from the N.
    But then the issue came up, in which the nikonian claims shooting in iso 200
    and lowering EV a stop with Nikon capture would give the exact same result
    as the noise free iso 100 image from the Canon.
    Still I'm unsure about this, if iso in camera was really only about
    processing, wouldn't the ISO be a parameter in raw processing like white
    balance or sharpness?

    What does the iso setting really do from the electronics point of view?

    Some expert opinions would be appreciated!

    Thanks
    Faiser, Nov 20, 2004
    #1
    1. Advertising

  2. "Faiser" <> writes:
    > I recently had an argument with a friend who claims that increasing
    > the iso setting does in fact the exact same thing as compensating
    > the exposure in post processing, but then inside the camera.
    > According to him, manipulating the levels after exposure would give
    > the same result. My idea is that on higher iso settings the sensor
    > is more sensitive to light which is not the same thing as achieving
    > this in post processing. Which of us is closer to the truth?


    You, mostly.

    The "ISO" setting on a digital camera is affecting the amplication of
    the electrical signal (voltage) from each sensor sensel when it still
    is in in analogue form.

    This is not making the sensor more sensitive to light (the intrinsic
    sensitivity of the sensor is indicated by its lowest ISO-rating), but
    it makes sure that the dynamic range of the analogue sensor data is
    distributed over the full 12 bits/channel that is the output of the
    A->D proccess that takes place in the camera. If the analogue signal
    had been noise free, this should in theory made high ISO as good and
    sliky smooth as low ISO. Of course, the signal is not noise free, so
    increasing amplification also increases noise - but if you get the
    exposure right, there should be 12 bits of data/channel in your
    RAW data.

    By comparison, underexposing and using levels to boost gives you
    data from the camera where the dynamic range is compressed into
    fewer bits/channel - so there is less data to begin with. If
    there was no noise, your image quality would still be degraded,
    because fewer bits/channel means that there will be some level
    of posterization.

    (However, note that Canon only uses analogue gain to get to ISO 1600.
    The "ISO 3200" provided by Canon on some models is in fact ISO 1600
    underexposed one stop, and the digitally level adjusted.)

    > Reason for our little argument was another C vs N discussion, where
    > the iso 100 of the C is supposed to be less noisy than the iso 200
    > from the N. But then the issue came up, in which the nikonian
    > claims shooting in iso 200 and lowering EV a stop with Nikon capture
    > would give the exact same result as the noise free iso 100 image
    > from the Canon.


    Huh? If I understand his workflow - this guy overexposes one stop
    and then darkens in post processing? Overexposing won't reduce
    noise. All he'll get is blown highlights and the same noise.

    > Still I'm unsure about this, if iso in camera was really only about
    > processing, wouldn't the ISO be a parameter in raw processing like
    > white balance or sharpness?


    True. But ISO in digital cameras isn't about (digital) processing -
    and therefore it must be controlled in-camera.

    > What does the iso setting really do from the electronics point of
    > view?


    Amplificaton of the sensor signal when it is in analogue form.
    (Think of it as like the "volume control" in a sound system.)
    --
    - gisle hannemyr [ gisle{at}hannemyr.no - http://folk.uio.no/gisle/ ]
    ========================================================================
    When you say you live in the real world, which one are you referring to?
    Gisle Hannemyr, Nov 20, 2004
    #2
    1. Advertising

  3. Faiser

    Guest

    In message <>,
    Gisle Hannemyr <> wrote:

    >Huh? If I understand his workflow - this guy overexposes one stop
    >and then darkens in post processing? Overexposing won't reduce
    >noise. All he'll get is blown highlights and the same noise.


    Hmmm. Whether or not you blow the highlights is a JPEG vs RAW or
    metering issue, but if you do not blow them, overexposing by a stop
    doubles the signal to noise ratio of the RAW data, and gives you an
    extra bit of depth in each color channel, as it concerns the subject. I
    Find that my Canon 20D tends to make very little use of headroom, and I
    often shoot with the camera set to +1 or +2 EC when there are no
    minority bright areas in a scene. +2 I use for low-contrast scenes on
    overcast days.
    --

    <>>< ><<> ><<> <>>< ><<> <>>< <>>< ><<>
    John P Sheehy <>
    ><<> <>>< <>>< ><<> <>>< ><<> ><<> <>><
    , Nov 20, 2004
    #3
    1. Advertising

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

It takes just 2 minutes to sign up (and it's free!). Just click the sign up button to choose a username and then you can ask your own questions on the forum.
Similar Threads
  1. JD

    How do you convert a CD ISO to DVD ISO?

    JD, Aug 20, 2004, in forum: Computer Support
    Replies:
    9
    Views:
    29,289
  2. Bill Smith
    Replies:
    1
    Views:
    846
    DaveJ
    Aug 1, 2003
  3. Salem Derisavi

    Figuring out ISO settings in Auto ISO mode

    Salem Derisavi, Sep 28, 2003, in forum: Digital Photography
    Replies:
    3
    Views:
    1,540
    Andrew McDonald
    Sep 29, 2003
  4. Georgette Preddy

    Is Sigma's SD10 at ISO 1600 better than Canon's 1Ds at ISO 100?

    Georgette Preddy, Jul 11, 2004, in forum: Digital Photography
    Replies:
    14
    Views:
    701
    Randall Ainsworth
    Jul 15, 2004
  5. cohibakid

    rebel 300d iso 100 vs nikon d70 iso 200

    cohibakid, Jul 14, 2004, in forum: Digital Photography
    Replies:
    4
    Views:
    584
    David J. Littleboy
    Jul 15, 2004
Loading...

Share This Page