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Thread: 'Noise' in digital photography

  1. #1
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    'Noise' in digital photography

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    If lower shutter speed introduces more noise into the photograph.. then shouldn't we always be taking photographs with the highest shutter speed that we can?
    Last edited by benny; 22nd Mar 2006 at 01:11.

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    It's the other way round. Higher shutter speed has more noise/grain. Shoot with the lowest shutter speed.

    Cheers,
    I have dwarf cichlids in my tanks! Do you?

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    what are you all talking about? it should be lower ISO (sensitivity) lower noise and higher ISO higher noise. so shoot with lowest ISO and whatever is the right shutter speed for the aperture and lighting available.
    why I don't do garden hybrids and aquarium strains: natural species is a history of Nature, while hybrids are just the whims of Man.
    hexazona crumenatum Galleria Botanica

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    Long day, late night. Confused. Thought he was talking about ISO speed!! Ha Ha!!

    Cheers,
    I have dwarf cichlids in my tanks! Do you?

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    he IS talking about ISO speed but then both of you write "shutter speed" haha
    why I don't do garden hybrids and aquarium strains: natural species is a history of Nature, while hybrids are just the whims of Man.
    hexazona crumenatum Galleria Botanica

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    LOL thought for a moment I've been teaching rubbish for the last 5 years..

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    no i was talking about shutter speed..
    read on dp review that certain shots with lower shutter speed got more noise..

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    Perhaps they're referring to the situation the shots were taken at.

    With limited amount of light, you have to bump ISO to get a higher shutter speed. Perhaps they were referring to long exposures or some circumstances where they couldn't get shutter speeds above 1/60th or so.

    ...or they could be referring to film perhaps? It'll be ASA values instead and as it gets higher there's indeed more noise (basically the equivalent of bumping ISO).
    Eric

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    Quote Originally Posted by ranmasatome
    no i was talking about shutter speed..
    read on dp review that certain shots with lower shutter speed got more noise..

    oh you mean that. the longer the exposure, the higher the probably that a sensor pixel site generates spurious signal. this is a characteristics of the sensor electronics, similar to the way your retina generates spurious signals in total darkness (i.e. in the absence of any received signals). if you try to see in total darkness, you will see spots and flashes, these are caused by spurious signals generated by the retina. In normal viewing light levels, these spurious signals will not be visible.

    in a digital camera, the same applies. the sensor will generate, statistically, spurious signals which becomes visible/significant during long exposure (in seconds) and very very dark scenes (e.g. astronomy photography). one way digital cameras reduces this noise is by repeat the exposure interval with the shutter closed (i.e. total darkness). then the signals "received" during this second exposure (which is ALL noise) is deducted from the first exposure (dark scene), hence effectively removing the noise from a long exposure.

    the canon 20D has extremely good noise performance in its sensor, hence the special 20Da version which is specially made for astrophotography.
    why I don't do garden hybrids and aquarium strains: natural species is a history of Nature, while hybrids are just the whims of Man.
    hexazona crumenatum Galleria Botanica

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    okay..so thsi only applies to really long exposure in dark areas then?? Thanks

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    One instance of it, yes. You can get it with underexposed pictures (shutter speed can vary from low to high). During post processing if you take an underexposed image and then correct it for exposure, you can see the noise, especially in the shadow areas.
    Eric

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    Quote Originally Posted by hwchoy
    in a digital camera, the same applies. the sensor will generate, statistically, spurious signals which becomes visible/significant during long exposure (in seconds) and very very dark scenes (e.g. astronomy photography). one way digital cameras reduces this noise is by repeat the exposure interval with the shutter closed (i.e. total darkness). then the signals "received" during this second exposure (which is ALL noise) is deducted from the first exposure (dark scene), hence effectively removing the noise from a long exposure.
    In my "film camera" days, there's a reciprocity error to calculate and compensate for time exposures. For good emulsions that have constant reciprocity error in all 3 colour layers, it is just an increase in aperture size or a multiplication of the exposure time. For poorer emulsions, a colour cast can result, so CC filters need to be added and its corresponding compensation then need to be factored in.

    I thought the ccd would have this pain licked from photographers of this generation.
    Warm regards,

    Lawrence Lee

    brothers, whatever is true, whatever is noble, whatever is right, whatever is pure, whatever is lovely, whatever is admirable--if anything is excellent or praiseworthy--think about such things.
    Philippians 4:8

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    Quote Originally Posted by Ibn
    One instance of it, yes. You can get it with underexposed pictures (shutter speed can vary from low to high). During post processing if you take an underexposed image and then correct it for exposure, you can see the noise, especially in the shadow areas.

    it appears that in digital cameras RAW format the effect of adjusting exposure is equivalent to adjusting ISO. so by boosting exposure you will get these noise which is the same as using a higher ISO in the first place.

    read it long ago in some forum or photo site.
    why I don't do garden hybrids and aquarium strains: natural species is a history of Nature, while hybrids are just the whims of Man.
    hexazona crumenatum Galleria Botanica

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    Quote Originally Posted by GaspingGurami
    In my "film camera" days, there's a reciprocity error to calculate and compensate for time exposures. For good emulsions that have constant reciprocity error in all 3 colour layers, it is just an increase in aperture size or a multiplication of the exposure time. For poorer emulsions, a colour cast can result, so CC filters need to be added and its corresponding compensation then need to be factored in.

    I thought the ccd would have this pain licked from photographers of this generation.
    With Nikon, it's more apparent in the consumer models, where the sensor heats up and produces a cast to the pics. Here's a couple of long exposures from the D70 with this effect.

    15 minute exposure



    4 minute exposure



    Due to this, I have been keeping exposures below 4 minutes. Stack the exposures if necessary.

    Canons are much better at long exposures, especially in the consumer models.
    Eric

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    Quote Originally Posted by hwchoy
    it appears that in digital cameras RAW format the effect of adjusting exposure is equivalent to adjusting ISO. so by boosting exposure you will get these noise which is the same as using a higher ISO in the first place.

    read it long ago in some forum or photo site.
    Yup, it's what is termed as pushing ISO.
    Eric

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    Quote Originally Posted by Ibn
    15 minute exposure
    Overheating sensor eh? Have you tried shooting time exposures in winter uninsulated? Does it show up when the camera is cold? Er... Stupid question, forget that I even asked. The batt would have died rendering the exercise useless unless you are using lithium and have wired it back to keep warm in your duvet.

    A quick way to correct this image, use Photoshop's Color Replacement Tool. Under tool options, for mode choose "Color", for sampling choose "once", for limits choose "discontinuous", tolerance 20-30%. option-click (alt-click) on the sky for the colour you want to replace in the magenta glow, then paint the pink away. You don't even need to be tidy with your painting.

    Quote Originally Posted by Ibn
    4 minute exposure

    .
    4 minutes is too fast to record a long enough trail of the stars in the sky to make the landscape dramatic IMO. It seems too short a time to get enough details in the shadow areas of the valley and the face on Half Dome. With sufficient detail in the shadows, one can make El Cap can stand out stark and eerily with use of blending modes in layers of Photoshop.
    Warm regards,

    Lawrence Lee

    brothers, whatever is true, whatever is noble, whatever is right, whatever is pure, whatever is lovely, whatever is admirable--if anything is excellent or praiseworthy--think about such things.
    Philippians 4:8

  17. #17
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    Hey Lawrence, thanks for the tip.

    Yup, it does show up in the cold; well depending on how cold you're talking about. That second picture with El Capitan was taken at 16F and the sensor still heated up.

    Tried using the color replacement in CS2, but the borders are still pretty apparent with the above. I'll have to revisit it later when I have more time. Lastly, wasn't trying to capture star trails in the 2nd shot above; more just for exposure of El Capitan instead (did I mention that it was 16F? ).
    Eric

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    Eric,

    I'll try to explain the logic behind my settings for Photoshop's Color Replacement Tool.
    Brush size: Choose a relatively big and soft brush.
    Mode: "Color" This will colourise ONLY your magenta glitch and not change any of the pixels.
    Sampling: "once" Means that the moment you click on the magenta glow, you won't alter any other colour in the sky nor the hut except for the magenta you first clicked.
    Limits: "discontinuous" So that the tool can jump over intermingling elements like your star trails and the hills on the horizon as the tool paints away the offending color.
    Tolerance: 20-30% to determine the limits CS2 will consider "within range" for the colour to be changed.

    You need to go at it over a few passes, clicking on a new shade of magenta at each new pass. You should be able to totally replace the colour of the glitch with that of the normal night sky. (I downloaded your image to test using the above setting and I cleared the offending colour in 10 passes, using a 41pixel brush size. There were some grey artifacts left over at the bottom left corner, probably resulting from the jpeg, but that's easy to clear with the rubberstamp tool, since it looks more natural to add in some star trails into the bit of horizon anyway).

    Yup, it does show up in the cold; well depending on how cold you're talking about. That second picture with El Capitan was taken at 16F and the sensor still heated up.
    It is not the ambient temperature but the temperature of the sensor that affects the colour cast. Looks like an opportunity open for an aftermarket TEC cooling company to work with the specialist department of camera companies.

    16F is not time to be out taking photos I had a nippy time out bivvyin outside Sunnyside in the early 80s because I was too cheap to pay for a camp permit and too broke to afford a tent. I was looking to join on anyone's rope to do a classic big wall Temperature was in the balmy late 40s not counting the windchill. Teeeth chatter for a tropicalised Singaporean. All I wanted then was a hot cuppa cha.
    Warm regards,

    Lawrence Lee

    brothers, whatever is true, whatever is noble, whatever is right, whatever is pure, whatever is lovely, whatever is admirable--if anything is excellent or praiseworthy--think about such things.
    Philippians 4:8

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