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Thread: Noise reduction techniques?

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    Super Moderator NEF.D90's Avatar
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    Noise reduction techniques?

    Saw this in another post and I would like some detail on noise reduction techniques. (NRT)
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    Administrator Aloicious's Avatar
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    I'm not ignoring you heh I've just been really busy at the hospital, this is our super busy time of year. I'll try to post some thoughts up later tonight when I get some downtime
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    Super Moderator NEF.D90's Avatar
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    Ok cool.
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    Administrator Aloicious's Avatar
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    So there are TONS of ways to reduce noise. some are better than others and some are better on some types of images than others...

    here's a basic way of doing it in camera raw:
    http://youtu.be/RQHcy_m9ixI

    which actually works pretty good, but on wildlife it can dull some of the fine details like fur/feathers.

    you can do a variety of blurring methods to reduce noise too

    like surface blur:
    http://youtu.be/2DmypF5bh2w

    or smart blur:
    http://youtu.be/aMqWi8y3KBE

    and you can mix and match various techniques together:
    http://youtu.be/HFsJSL8ddSg

    you will have to play around with different techniques with different images to find what works best on them. and remember what the final use of the image is, if you're downsizing it just for the web, then the act of downsizing will naturally take care of lots of noise and you can usually go very light on the actual noise reduction (or none at all if you like), but if you're upsizing for print or something, then you may have to be a little more heavy handed since upsizing will accentuate the noise.

    a fairly common workflow for me is to use the camera raw noise removal very lightly, just enough to take an edge off, but leaving as much detail as I can. Then in PS I'll put a light surface blur on it to clean up backgrounds, and edge or hand paint a mask so that it isn't affecting the subject...something like that...and noise reduction should be done prior to any sharpening....basically sharpening should be one of the last things you do before you save (after the image is at it's final size) where noise reduction, should be one of the first (before image size is altered)
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    Resident Canon Guy kamokevin's Avatar
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    I've read that sensor heat can also cause noise, such as when the sensor heats up due to long exposure photography and multiple long exposures taken over a long period of time. I haven't shot for more than about 30 minutes continuously so I haven't experienced it I don't think, but I plan to shoot for longer intervals in the future. Is this something to worry about, or is it insignificant enough to be ignored?
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    Long exposures will heat up the sensor, but I believe it is over 30 seconds or longer, and more than one; and not shooting off a bunch of exposures quickly. But I have never actually seen an exact number.
    However, knowing electronics, a CCD (charge coupled device) tends to heat up more than a CMOS (Complementary Metal Oxide Semi-Conductor) sensor. I believe (but not totally sure), CCDs are primarily used on medium to large format cameras now.



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    Administrator Aloicious's Avatar
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    yup the sensor will heat up with long exposures, its an issue with astrophotography and such...if you are looking in the camera menus there is an option called 'long exposure noise reduction' which basically takes a second exposure of equal length right after your initial exposure, but without the shutter open, then it kindof subtracts the averages of the noise out of the original frame from the noise collected in the dark frame as best as it can...so for example if you take a 30 second exposure, it'll take 30 seconds for the original exposure and 30 seconds for the dark exposure.

    this is also something that can be done manually (i.e. not in-camera) even with multiple 'dark' exposures, and is known as 'taking darks' which many astrophotography guys do because doing your own darks subtraction gives a bit more control but also takes more time and effort in post production.

    the in camera long exposure noise reduction does pretty well for most things, but learning to remove your own can also be beneficial especially if you get into things like astrophotography.
    -Justin

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    Administrator Aloicious's Avatar
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    Quote Originally Posted by f5fstop View Post
    Long exposures will heat up the sensor, but I believe it is over 30 seconds or longer, and more than one; and not shooting off a bunch of exposures quickly. But I have never actually seen an exact number.
    However, knowing electronics, a CCD (charge coupled device) tends to heat up more than a CMOS (Complementary Metal Oxide Semi-Conductor) sensor. I believe (but not totally sure), CCDs are primarily used on medium to large format cameras now.
    .
    not sure about the actual heat put off by the sensors, but CCDs are typically preferred to CMOS in astrohpotography because they tend to handle the noise at long exposures better. CCDs are also fairly common in small cheap sensors like webcams, etc. but most of the super expensive astrophoto rigs are based off of CCD sensors (usually monochrome too)...
    -Justin

    Bodies - D800E
    Lenses - Sigma 18-35 f1.8 DC | Zeiss 15mm f2.8 ZF.2 | Zeiss 21mm f2.8 ZF.2 | Sigma 35mm f1.4 Art | 105mm f2.5 AI-S | 70-200 f2.8G VRII | 200mm F4.0D Micro AF | 300mm f2.8 VRII

    My PhotographyWild Blog

    C&C is always welcome on the images I post.

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    Resident Canon Guy kamokevin's Avatar
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    Quote Originally Posted by Aloicious View Post
    yup the sensor will heat up with long exposures, its an issue with astrophotography and such...if you are looking in the camera menus there is an option called 'long exposure noise reduction' which basically takes a second exposure of equal length right after your initial exposure, but without the shutter open, then it kindof subtracts the averages of the noise out of the original frame from the noise collected in the dark frame as best as it can...so for example if you take a 30 second exposure, it'll take 30 seconds for the original exposure and 30 seconds for the dark exposure.

    this is also something that can be done manually (i.e. not in-camera) even with multiple 'dark' exposures, and is known as 'taking darks' which many astrophotography guys do because doing your own darks subtraction gives a bit more control but also takes more time and effort in post production.

    the in camera long exposure noise reduction does pretty well for most things, but learning to remove your own can also be beneficial especially if you get into things like astrophotography.
    Ah ok, I have had long exposure noise reduction on whenever doing astrophotography stuff, so that may be why it was never a huge issue. I'm not sure I can do it manually with GIMP; i'll have to look for a tutorial. I'll spring for photoshop one day.
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