How does ISO setting work?

Discussion in 'Digital Point & Shoot Camera' started by David Arnstein, Jul 15, 2005.

  1. The digital cameras that I have seen have a feature that allows the
    user to choose an ISO setting. I would like to know what this feature
    does, since I suspect that it is useless.

    My concern is that setting a high ISO number simply
    1. Causes the camera to take pictures that are quite dark
    2. Post processes the picture by increasing the brightness, in
    software.

    If this is the case, then I prefer to increase the brightness myself,
    in Photoshop.

    On the other hand, if the ISO adjustment on the camera actually
    changes the physical properties of the photosensor, then it's a
    different story.

    I'd like some feedback on this before I spend my time experimenting
    with different ISO settings.
     
    David Arnstein, Jul 15, 2005
    #1
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  2. David Arnstein

    Your-Nice Guest

    iso settings are to do with how sensitive your sensor is to light , the
    higher the iso setting i.e 400-800 1600 means you could take a photo in a
    dimmer room than iso 100 or 200.
     
    Your-Nice, Jul 15, 2005
    #2
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  3. David Arnstein

    tsingh Guest

    ISO does not change the physical properties of the photosensor, it
    simply brightens the image as you suggest. There is, however, one
    crucial difference. It amplifies the signal before digitizing it, and
    this keeps down the quantization noise.

    -T
     
    tsingh, Jul 15, 2005
    #3
  4. David Arnstein

    Marvin Guest

    Not quite correct. The ISO setting doesn't change the sensor at all. It changes the
    amplification in the readout. I

    The picture won't come out dark unless oyu use the wrong ISO setting. Most digicams let
    you use auutomaic ISO setting as part of a point-and-shoot setting. It works properly
    most of the time.

    No. it increases the amplification by the camera's electronic hardware.
    You can do that up to a point. If the exposures are really bad, Photoshop or any progam
    can't do the job well.
     
    Marvin, Jul 15, 2005
    #4
  5. David Arnstein

    JPS Guest

    In message <db8u3k$l19$>,
    That should not be a problem. If anything, high ISO images should be
    brighter if they are different in brightness, either because there is
    not enough light for a low ISO image, or the cameras has run out of
    shutter speeds or wide aperture to keep the high ISO image from
    over-exposing.
    Some cameras achieve their highest ISOs this way, and get the lower
    range by varying the gain applied to the sensor capture before it is
    turned into numbers. Perhaps some do all of their ISOs this way, but I
    don't know how many.
    The normal way does not change the sensor at all; the sensors are fixed
    in their sensitivities. The difference between ISOs is usually achieved
    by amplifying the signal by different amounts, causing different ranges
    of sensor voltages to map to the range of RAW data, usually 0 to 4095.
    Experimenting will tell you more than other people usually can, and more
    than what the manufacturer will tell you.

    If the camera has manual exposure, set it up on a tripod or table to
    take an image with a full range of tones, and make a normal exposure at
    the camera's highest ISO. Now, keep the f-stop and the shutter speed
    the same, but set it to the lowest ISO. Boost the exposure level of the
    low-ISO image in software to match the high-ISO. If the high-ISO image
    has less noise and more detail, then the camera may be using
    amplification in hardware, and then you are clearly better off using
    high ISO than under-exposing a low ISO image (or having too long a
    shutter speed at a low ISO). Even if the camera is using amplification,
    if it is JPEG-only, it may be that the camera kills shadow detail when
    making a JPEG, to hide noise, in which case you will get poor images if
    you boost the exposure, anyway. You can also try the different ISOs
    with the same image, and automatic exposure. If the quality
    deteriorates rapidly as you go to higher ISOs, then there is probably no
    amplification. If the quality is only a little bit worse at each higher
    ISO, there is probably amplification. It is also possible that there is
    amplifiaction, but it has a lot of noise and distortion.

    This is a complex issue, with usually no details coming from the
    manufacturer.
    --
     
    JPS, Jul 15, 2005
    #5
  6. David Arnstein

    Matti Vuori Guest

    Could you please post in one group only...
     
    Matti Vuori, Jul 15, 2005
    #6
  7. I love usenet and I endeavor to be a "good citizen" in this space. I
    am very interested in your post.

    Would you please explain your reasoning. Here is mine:

    1. My post is relevant to all three news groups.
    2. By cross-posting, I arrange that an individual using a decent
    newsreader will only see my post once, even if he habitually reads
    all three news groups.

    I look forward to your response Mr. Vuori.
     
    David Arnstein, Jul 16, 2005
    #7
  8. I think Matti's post equates to, "I'm not using a decent
    news reader and don't know how Usenet works."
     
    Andy Sullivan, Jul 16, 2005
    #8
  9. Following that line of reasoning, isn't your post relevant in
    rec.photo.digital.zlr as well?

    But your reasoning is flawed. If something is of general interest, it
    should only be in rec.photo.digital. The aim of splitting the newsgroups
    was to reduce the number of postings, and help people focus on their own
    interest better. There was no intention to replace the rec.photo.digital
    group.

    It would be better to restrict your posting to just one group if possible.

    Thanks,
    David
     
    David J Taylor, Jul 16, 2005
    #9
  10. David Arnstein

    Ron Hunter Guest

    Vastly oversimplified:
    The ISO number is like an amplifier volume setting. The larger the
    number the 'louder' the light output from the sensor. And, like a sound
    amplifier, excessive settings often produce very distorted, and
    'clipped' output. The lower the ISO setting, the more light you need
    for a usable picture, but the higher the setting, the more the output
    from the sensor is amplified, and the more 'noise', and 'distortion' you
    will see. Many cameras use software to improve the image quality, and,
    since they have access to the original output from the sensor, they can
    usually do this better than Photoshop.
     
    Ron Hunter, Jul 16, 2005
    #10
  11. David Arnstein

    Don Stauffer Guest

    The ISO setting is one parameter the exposure computer uses to determine
    exposure (shutter speed and aperture [lens opening]). The default value
    should give you the best balanced exposure. There IS now a definition
    of the ISO exposure for digital cameras, but I can't find it right now.

    You can push a digicam just as you can push a film camera by dialing in
    a higher ISO value, which causes a smaller exposure (less energy) than
    for the nominal value. This either shortens shutter speed, reduces
    aperture, or both, depending on the exposure 'mode' you are using.
     
    Don Stauffer, Jul 16, 2005
    #11
  12. David Arnstein

    Don Stauffer Guest

    Gee, while I was not the originator of the comment, I guess I myself do
    not know how to set up my reader so that it doesn't show up cross posts.
    I use Thunderbird. What do I have to do to keep from downloading and
    seeing cross posts between rpd and rpe35?
     
    Don Stauffer, Jul 16, 2005
    #12
  13. David Arnstein

    Don Stauffer Guest

    I guess I'd argue with this. The sensor (the CCD chip) has the same
    output regardless of the amplifier gain. If we push by using a higher
    ISO setting, which results in less exposure, there will be fewer
    photoelectrons in each well, and the CCD readout signal will be lower.
    One can amplify signal AFTER the readout, but the sensor output is lower
    when pushing exposure.
     
    Don Stauffer, Jul 16, 2005
    #13
  14. David Arnstein

    Paul Mitchum Guest

    Typically, a newsreader will only download a crossposted article once.
    This message, for instance, is crossposted to three newsgroups. See the
    Newsgroups: line, count three. :)

    So it'll get downloaded once, and then show up listed in any of the
    three groups. If you read this message (I hope you do..), then it will
    be marked as read for all three newsgroups.

    Your newsreader should work this way without changing any settings. If
    it doesn't, get a new newsreader.

    If I had reposted this message three times, one for each newsgroup, then
    (assuming you read all three newsgroups) it would be downloaded three
    times, and you'd have to read it three times.

    This is why crossposting is preferred to reposting, and why spammers
    prefer reposting to crossposting.
     
    Paul Mitchum, Jul 16, 2005
    #14
  15. David Arnstein

    Boat Guest

    Gosh. Here's one instance where Outlook Express manages to meet
    expectations. It correctly filters crossposts that are marked as already
    read.
     
    Boat, Jul 16, 2005
    #15
  16. If you don't like cross-posting, simply set your kill
    filter so you don't see those posts, hypocrite. Your whining
    just increasing the damn noise level.
     
    Eru Ilúvatar, Jul 17, 2005
    #16
  17. David Arnstein

    Neil Ellwood Guest

    Use Pan instead?
     
    Neil Ellwood, Jul 17, 2005
    #17
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