What Creates Noise/Grain At Higher ISO Speeds?

Discussion in 'Photography' started by Matt, Nov 14, 2004.

  1. Matt

    Matt Guest

    What is the actual reason why photos shot at higher ISO speeds create

    In film, I can understand that to produce films which is more sensitive to
    light, the chemistry may be different, but why is this evident with digital?

    If you look here, noise is very evident in this digital shot, but I am
    puzzled why it occurs:
    Matt, Nov 14, 2004
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  2. Matt

    JPS Guest

    In message <cn858s$5f1$>,
    Do you realize what you are looking at there? (Most of) the image was
    highly sharpened with no noise-reduction, and this is at ISO 1600. You
    are looking at what would be a 40 inch by 27 inch full image, if your
    monitor were big enough to display it; that's over 3 feet wide. Also,
    the optics are at the limits of their resolution, so there is no
    high-contrast image detail to compete with the noise. The noise got
    sharpened more than the detail. Look at the left and bottom edges;
    there is no sharpening there.
    JPS, Nov 14, 2004
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  3. Matt

    Matt Guest

    The point of this example was not to say this was a poor photo, just to give
    an example of noise. It was chose randomly only as an example of noise.

    If I knew this would upset people, I would not have included the link. I
    included the link purely as an example.

    I hope I have not offended anyone.
    Matt, Nov 14, 2004
  4. Matt

    JPS Guest

    In message <cn868u$s56$>,
    No one is upset or offended. I was just bringing to your attention that
    this is a crop; it is less than 5% of the full image, are-wise, and
    about 22% of the image in each dimension. There are woods surrounding
    the carton, and a female Cardinal looking at the container, in the
    original image.

    You would not see this noise in an 8x10 inch print! You would barely
    see it in a 16x20, if most of the original image was included.

    I used a small, 100% crop because I was demostrating a lens combo at the
    pixel level, and didn't need the rest of the image.
    JPS, Nov 14, 2004
  5. Matt

    dylan Guest

    Amplification of the signal, they also amplify the noise thats present , as
    well as the low level signal at higher ISOs.
    dylan, Nov 14, 2004
  6. Matt

    BillB Guest

    I can guess why by way of analogy, and I don't know if it's
    accurate or not, but until a better explanation comes along it'll
    do, at least for me. If you consider AM/MW radios, reception is
    good when stations are nearby and produce strong signals. When
    signals are weak, you turn up the volume, but probably notice that
    the fidelity isn't quite so good. When signals are *really* weak,
    as for example when trying to listen to distant shortwave signals,
    you might have a better radio that has an additional RF gain control
    that can be used to make the radio more sensitive. But now the
    station's signal might be really weak and be "buried in the noise".
    Some of this noise consists of weak natural or man-made signals that
    are also picked up by the radio. There's not a lot that can be done
    about this. But not all of it is. Some of the low level noise is
    created by the radio's own circuits (and might be due to quantum
    phenomena). Very good radios use "low noise" components.
    Transistors, resistors, etc. A look at manufacturer's data sheets
    will show which "low noise" transistors should be used in RF
    circuits if noise is to be minimised. I imagine that the same thing
    happens in the circuits that the camera sensors are used in. You
    can increase the amplification (boost the ASA speed), but at the
    cost of making the background noise (which was always there) more
    apparent, since it is relatively constant, while the desired image's
    signal becomes weaker (if it wasn't weaker you wouldn't have boosted
    the film speed).
    BillB, Nov 14, 2004
  7. Matt

    bmoag Guest

    Many of the explanations for noise in electronic sensors are based on the
    technical limits of the early digital technology we are still using. As such
    they are misleading.

    One of the misconceptions is that smaller digital sensors can never yield
    the lower noise now seen in larger sensors. The fact is that noise levels
    will decrease in all digital sensors as more experience is gained in the
    design and manufacture of these devices. So will the dynamic range of light
    values the sensors are able to capture. Claims to this effect are already
    being made for the newest Canon and Fuji dSLRs.

    Manufacturer's claims, like those of politicians, occasionally coincide with

    The most important limiting factor in reducing the size and performance
    (regardless of sensor size) of high resolution digital sensors has nothing
    to do with sensor technology but has to do with the inherent properties of
    light, reflection (above and within the sensor), diffaction and the
    inescapable problems of bringing all color light rays into focus at the same
    plane. The sort of optical noise that is caused by the intereacting
    properties of light, lenses and the flat plane of digital sensors
    (regardless of sensor size) is already underappreciated in evaluating the
    performances of current digital cameras. Because of these effects the
    designs of lenses for high end digital cameras are going in directions that
    film cameras did not require.

    Software may be part of the solution. Programs already exist for
    post-exposure tweaking of vignetting, barrel and pincusion distortion but
    they require manual tweaking. Who knows what the future will bring? Olympus
    has publicly stated it is moving toward building this sort of post-exposure
    processing into its dSLR line.
    bmoag, Nov 14, 2004
  8. Matt

    Alan Browne Guest

    Film suffers larger physical grain (dye clouds) in the plane of the film (call
    it x,y) as the ISO goes up. Faster speed = larger 'grain' or dye clouds. This
    results in the grain that you see. It's not really that cut and dry, but the
    end result is coarseness in the negative image that we call "grainy".

    In digital, the x,y is constant regardless of the sensitivity... the grain size
    will always be the same for a given sensor. However, the noise level will be
    different from pixel to pixel, and this difference is amplified by the
    increasing sensitivity... that is what gives the noisy 'grainy' look on high ISO
    digital shots. The 'grains' remain the same size, but there is a greater
    dynamic difference between them due to noise. This is more complex than that,
    as each pixel that you see from most SLR's is a composite of several pixels of
    different color. The noise response in, eg, red, green and blue channels is
    different for each color and this further makes pixel to pixel noise differences
    more apparent in the resulting end pixel.

    Hope that helps.

    -- r.p.e.35mm user resource: http://www.aliasimages.com/rpe35mmur.htm
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    Alan Browne, Nov 14, 2004
  9. Matt

    Alan Browne Guest

    See my other reply.
    And a good thing you did.
    Nah. Don't worry about assorted crankies.


    -- r.p.e.35mm user resource: http://www.aliasimages.com/rpe35mmur.htm
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    -- e-meil: there's no such thing as a FreeLunch.
    Alan Browne, Nov 14, 2004
  10. Matt

    Alan Browne Guest

    I believe the gent wanted to know "why is this so?" and not have a blast over
    his particular posted example.


    -- r.p.e.35mm user resource: http://www.aliasimages.com/rpe35mmur.htm
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    -- [SI rulz]: http://www.aliasimages.com/si/rulz.html
    -- e-meil: there's no such thing as a FreeLunch.
    Alan Browne, Nov 14, 2004
  11. What happens in a digital camera is that light entering the sensor creates a
    voltage at each site. If we assume that any sensor site peaks at say 1
    volt, then that's the point of white saturation. In a proper exposure, it
    would be nice to have no voltages at 1 but at least some close to 1 for the
    very brightest details in the scene. Now, suppose the scene is darkish and
    the highest voltage recorded is only 1/10 of a volt. Not a big problem in a
    digital camera, since amplifiers with a multiplication factor of 10 (called
    a voltage gain of 10) can beef up all the sensor signals before the
    information is converted to digital form. However, the gain of 10 also
    multiplies the noise by a factor of 10. So, when you shoot a scene at a
    high ISO, you are using high gain and seeing noise that you ordinarily would
    not see. Hope this helps. Tune an FM radio receiver to a frequency where
    there is no station and the hiss that you hear is aural noise. Look at a TV
    displaying a weak signal and the grain that you see is noise.
    Charles Schuler, Nov 14, 2004
  12. While the responses so far are close to the answer, what I've seen
    is not quite complete. Noise is due to several things, including
    read noise, thermal/shot noise, and photon noise. Read and
    thermal noise will dominate in longer exposure images. In short
    exposure images, photon noise can dominate (probably depends
    on the camera). Newer cameras, and especially DSLRs, which
    use low noise electronics, most will likely be photon noise
    limited for daytime scenes (exposures up to at least a fair
    fraction of a second.

    Photon noise limit: what does it mean? When counting photons,
    the noise is the square root of the number of photons
    counted. This is a fundamental physical limit.
    For electronic sensors, the number of photons
    counted is dependent on the quantum efficiency (which is
    very high), and the size of the pixel (proportional
    to the number of photons that can be collected per unit
    time), and the electron well capacity of the device
    (also generally scales with the size of the pixels).

    A high-end camera, like the Canon 1D Mark II, which has
    pixel spacing of about 8 microns, has a full well
    capacity of a little over 52,000 electrons. That means
    the noise at maximum signal is sqrt(52000) = 228, and the
    maximum signal to noise is 52000/sqrt(52000) = 228.
    At lower signal, the noise is less, but so is the
    signal. For example, at half capacity, 26000, the signal
    to noise is 161.

    For a camera with smaller pixels, and smaller full well,
    the total noise is less, but so is the signal. Let's assume
    a sensor with 4-micron pixels and a full well capacity
    of 13,000 electrons. The maximum signal to noise is
    only 114.

    I've described the signal to noise of the 1D Mark II at:
    and show that it is working at the photon noise limit.
    In particular, wee figure 2. This means
    photon nose is the fundamental limit for that sensor.
    The only way to improve on these values is to increase
    the pixel area and full well capacity. Like I said above,
    other digital cameras are likely working at the photon noise
    limit too. The smaller sensors will never improve on this
    fundamental limit, at least as we understand physics today.

    Film is probably also photon noise limited, but since its
    quantum efficiency is very low, the signal to noise is much
    lower too. See figure 1 on the above page. For faster film,
    the larger grains are collecting fewer photons, so one would
    expect that the signal to noise would drop. My web page
    shows noise levels ~4 times worse for film compared to
    electronic sensors at similar ISO values, consistent with
    the lower quantum efficiency.

    So, if you want lower noise images, buy a camera with a
    larger sensor to collect more photons for a given exposure.

    Roger Clark
    Photos, other digital info at: http://clarkvision.com
    Roger N. Clark (change username to rnclark), Nov 14, 2004
  13. Matt

    JPS Guest

    In message <GSOld.14324$>,
    No one is being cranky. I replied as I did because he may have thought
    that it was an entire image shrunk to web size.

    Noise of that magnitude with strong sharpening in a pixel-for-pixel crop
    is to be expected.
    JPS, Nov 14, 2004
  14. Hi

    A higher ISO speed allows you to shoot better pictures in low light
    conditions. A higher ISO speed allows you to use a faster shutter
    speed and/or a smaller aperture in a given light level.

    The drawback of higher ISOs are as follows:
    - Increased noise
    - Larger file sizes — you'll get far fewer shots per memory card at
    ISO 800 than at ISO 100.
    - Reduced shadow detail and sharpness

    The same problem exists for analog cameras when you use fast film.

    Gary Hendricks
    Gary Hendricks, Nov 15, 2004
  15. Matt

    Alan Browne Guest

    sigh... again, he wants the "why" not the "what".


    -- r.p.e.35mm user resource: http://www.aliasimages.com/rpe35mmur.htm
    -- r.p.d.slr-systems: http://www.aliasimages.com/rpdslrsysur.htm
    -- [SI gallery]: http://www.pbase.com/shootin
    -- [SI rulz]: http://www.aliasimages.com/si/rulz.html
    -- e-meil: there's no such thing as a FreeLunch.
    Alan Browne, Nov 15, 2004
  16. Matt

    Harvey Guest

    Harvey, Nov 15, 2004
  17. Matt

    Ken Weitzel Guest


    Me too - all I can possibly think of is that he's
    suggesting that noisy pictures don't jpeg compress
    quite as much as clean ones? :)

    Take care.

    Ken Weitzel, Nov 15, 2004
  18. Matt

    JPS Guest

    In message <sRUld.25081$>,
    Look, I have no responsibility to choose between giving a person exactly
    what they asked for, or to remain silent. There are plenty of people
    here capable of answering questions. I only say something when I think
    something *needs* to be said.
    JPS, Nov 15, 2004
  19. Digital: nominal background radiation (random noise) from many sources,
    including the Big Bang, is always stimulating the sensor. At low ISO
    settings, the strength of the light coming throught the lens (signal) is so
    much greater than this background noise that you don't see it. The higher
    the ISO, the lower the signal to noise power ratio.

    Film: film is made more sensitive by simply putting more silver halide
    (thicker) on the film. When wet and developing, the sensitized silver tends
    to be cohesive in the emulsion and clump together. The thicker the
    emulsion, the bigger the clumps or "grains". Also thicker emulsions
    required longer developing times and this gives the silver more time to move
    around and form bigger grains.
    Dominic Richens, Nov 15, 2004
  20. Matt

    Alan Browne Guest

    Alan Browne, Nov 15, 2004
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