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EPM1: Noise Reduction vs. Noise Filter

Discussion in 'Olympus Cameras' started by WT21, Dec 31, 2011.

  1. WT21

    WT21 Super Moderator Subscribing Member

    Feb 19, 2010
    Posted this at DPR, too, but lately there's nothing but fighting going on over there. Not sure if I'll get a real answer, so here goes at mu, too :) 

    Does anyone know how/if the Noise Reduction and Noise Filters interplay with each other?

    From the EPM1 manual (p85)
    Noise Reduction:

    "This function reduces the noise that is generated during long exposures. [Auto]: Noise reduction is only performed at slow shutter speeds.
    [On]: Noise reduction is performed with every shot. [Off]: Noise reduction off. • Noise reduction requires about twice the time needed to
    record the image. • Noise reduction turns off automatically during sequential
    shooting. • This function may not work effectively with some shooting
    conditions or subjects."

    Noise Filter:

    "Choose the amount of noise reduction performed at high ISO sensitivities."

    I can make guesses and conjecture at what this means. I'm wondering if anyone here has done testing or somehow else actually KNOWS how/if these two settings interact? For instance, do you need Noise Reduction ON, and then Noise Filter controls the strength?

    If they are independent, then how do they differ?

    Thanks for any help/insight.
  2. crsnydertx

    crsnydertx Mu-43 Top Veteran

    Dec 31, 2010
    Houston, TX
    Bill, the one thing that jumps off the page at me is that use of the noise reduction requires twice the time needed to record the image. That says to me that the ideal selection for this feature is "off". For me, noise reduction is best taken care of in post-processing, particularly with RAW images.
  3. Jonathan F/2

    Jonathan F/2 Mu-43 Hall of Famer

    Aug 10, 2011
    Los Angeles, USA
    Noise reduction only seems to work on single shooting mode. It defaults to off when shot on either high or low shooting.
    • Useful Useful x 1
  4. Art

    Art Mu-43 All-Pro

    Mar 13, 2011
    San Francisco, CA
    I think NR affects raw files also and not just jpegs like Noise Filter. I always leave NR on for night long exposure shots because it takes care of dark frame substraction (in RAW). Noise filter affects jpegs at ALL ISO settings. I set it to off by default and only turn it to Low for ISO800-1600. Noise is not seen at normal viewing sizes but you'll be reducing sharpness if leave NF on at ISO200
  5. crsnydertx

    crsnydertx Mu-43 Top Veteran

    Dec 31, 2010
    Houston, TX
    According to some posts in the 4/3 Forum, Olympus has acknowledged that indeed noise REDUCTION is applied to RAW images before they're saved to the SD card. I'm glad to know that; now I'm sure I'll keep noise reduction off. I don't believe a camera algorithm can be as sophisticated as post-processing software in reducing noise without smearing details. Olympus needs to put an asterisk beside their use of RAW....sounds like partially cooked to me!:rolleyes: 
  6. whatisinthebag

    whatisinthebag Mu-43 Regular

    Dec 23, 2011
    Central California
    This is a most excellent discovery. I'm finding my higher ISO raw files much more tolerable now.

    +1 to the asterix on the PM1/PL3 raw format
  7. Aegon

    Aegon Mu-43 Veteran

    Nov 3, 2011
    Portland, OR
    Noise reduction cannot be done as effectively during post processing. The whole point is that noise reduction uses the same environmental conditions as the exposure to determine how the sensor generates noise under the circumstances. Find more details by searching for Dark Frame Subtraction (DFS): Dark-frame subtraction - Wikipedia, the free encyclopedia

    Noise filter is an algorithmic approach to noise removal, which often comes at the expense of image detail. Which is to say that your computer probably does it better, but if you turn it on in-camera then you can bake some nice easy JPGs without having to do a PP step.
    • Like Like x 1
  8. crsnydertx

    crsnydertx Mu-43 Top Veteran

    Dec 31, 2010
    Houston, TX
    Aegon, thank you for that. Do we know for sure that Olympus is doing dark-frame subtraction with their noise reduction algorithm? I guess I should do some more reading and experimentation before I take a firm stand. :thumbup:

    Re noise filtering, if it's only affecting the JPEG it's not that important to me. I do RAW + JPEG by default, so the JPEG is not necessarily my final product. I enjoy post-processing, so that's not much of a factor either.
  9. relic

    relic Mu-43 Top Veteran Subscribing Member

    Oct 21, 2010
    North Carolina, USA
    I think that exposure with noise reduction on takes twice as long as with it off is strong indication that it is doing dark-frame subtraction.
    • Like Like x 1
  10. Promit

    Promit Mu-43 All-Pro

    Jun 6, 2011
    Baltimore, MD
    Promit Roy
    Noise reduction is definitely dark-frame subtraction, and you almost certainly want it if you can spare the time.
    • Like Like x 3
  11. BarefootPilgrim

    BarefootPilgrim Mu-43 Top Veteran Subscribing Member

    Dec 23, 2009
    Westchester, IL
    To quickly answer your question, no, these do not interplay with each other. They're two separate and distinct phenomena.

    To elaborate...

    As Olympus defines it, "Noise Reduction" (sometimes called "Dark Frame Subtraction") is the process that shuts off "hot" pixels during extended use of the imager. This usually occurs only during long exposures when the imager is active and recording for an extended period of time (several seconds or more) and the pixels do, in fact get hot (or at least warmer than normal). It does affect RAW data in the sense that the hot pixels are turned off and therefore do not add data to the ORF file.

    Olympus defines "Noise Filtering" as the process of smoothing the noise that's generated at all exposures at the edges of each pixel -- what we usually refer to as "noise" when we talk about the blotching and smearing every pixel-peeper on the internet complains about.

    "Noise Filtering" is the stuff many of us do in post."Noise Reduction" is best done in the camera, although some post-processing software claims it can handle this, too. (Not sure that I buy into that claim, however.)

    One more note... Noise Filtering is applied only to the jpeg version of your photo, not the RAW version. There are some folks who maintain that some camera makers also apply an amount of Noise Filtering even to RAW data. but I've yet to see any proof of that belief in my own work.
    • Like Like x 4
  12. crsnydertx

    crsnydertx Mu-43 Top Veteran

    Dec 31, 2010
    Houston, TX
    WT21: Thanks for starting this thread. I've learned a LOT from it!
  13. WT21

    WT21 Super Moderator Subscribing Member

    Feb 19, 2010
    Thanks for all the help!
  14. jaygee

    jaygee Mu-43 Rookie

    Dec 15, 2011
    Brighton, Ontario
    Good information!!! Thank you.
  15. jaygee

    jaygee Mu-43 Rookie

    Dec 15, 2011
    Brighton, Ontario
    Good information! Thank you.
  16. MajorMagee

    MajorMagee Mu-43 All-Pro

    Feb 24, 2011
    Dayton, OH
    Small correction to something stated earlier. Noise Reduction, or Dark Frame (or Field) Subtraction does not shut off hot pixels like pixel mapping does.

    It could be thought of more like a real time calibration step. As you take an image with a long exposure the difference in responsiveness between each individual sensor site starts to add up to distortions of the data being captured. These differences come from variations in the manufacturing in the sensor array, and each site's unique response to environmental conditions. By immediately taking an equal data capture with no light falling on the sensor (shutter closed), the software is able to subtract this background variation from the image you just captured. This is done after each shot (hence doubling the time) to get this calibration data as close to the identical conditions of your image capture as possible.
  17. fdifulco

    fdifulco Mu-43 Veteran

    Nov 28, 2011
    New Orleans, Louisiana
    one more item on noise reduction

    if you want to speed up your night ****s, like fireworks, you want to turn off noise reduction. i kept wondering why it was taking so long to write and then went and checked. i had forgotten noise reduction on. turned off and got the fast writes.
  18. dhazeghi

    dhazeghi Mu-43 Hall of Famer Subscribing Member

    Aug 6, 2010
    San Jose, CA
    DFS doubles exposure time. In order to account for hot pixels, the length of exposure for the dark frame is identical to the length of the exposure for the actual frame.

  19. Brianetta

    Brianetta Mu-43 Veteran

    Sep 5, 2010
    North East England
    Brian Ronald
    If you're photographing fireworks a lot, you can take a few reference frames with the lens cap on, at the beginning and end of the display, and use those to help reduce noise later. Alternatively, there's normally a lot of black background where fireworks are concerned, so at a push one could even use those to build a composite dark frame.

    It's not perfect, of course. No compromise is.
  20. chuenmasiello

    chuenmasiello Mu-43 Regular

    Jun 29, 2012
    Pixel mapping does not shut off hot pixels.

    Quote from Olympus:

    What is Pixel Mapping?

    The CCD, CMOS, and NMOS sensors used as film in digital cameras are made up of millions of pixel sites that are microscopic photodiodes—charged electronic elements that respond to light. These pixels may cease to function over time or may not even be functional when the sensor is manufactured. There are two types on non-functioning pixels:

    Dead Pixels: A pixel that reads zero or is always off on all exposures. This state produces a black pixel in the final image.
    Stuck Pixels: A pixel that always reads high or is always on to maximum on all exposures. This produces a white pixel in the final image.
    When a digital camera is manufactured, one of the quality control steps is Pixel Mapping. In this process the sensor is checked for dead or stuck pixels. When such pixels are found, a radial interpolation explores the pixels around the dead or stuck pixel, maps their locations, and inserts data enabling the camera to mimic what the dead or stuck pixel should be doing.

    Over time, all sensors will develop dead or stuck pixels. They can be cloned out using image post-processing software, but this can be time consuming. The majority of camera brands require that the camera be sent to a service facility to have the sensor re-mapped by a technician, which can be costly and means the user will be without a camera while re-mapping is being done.

    Olympus incorporates Pixel Mapping in the firmware of its digital cameras so that the user can perform Pixel Mapping as necessary or as preventive maintenance and not have to send the camera in to a service center to have the sensor re-mapped. We recommend once a year. Look in the menu for PIXEL MAPPING. The process only takes a few seconds. Some of the earlier Olympus models have Automatic Pixel Mapping (APM) that re-maps the sensor when the batteries are replaced.

    Pixel Mapping will not repair dead or stuck pixels in an LCD screen—this requires that the LCD be replaced by repair.

    “Hot Pixels” are not to be confused with dead or stuck pixels. A hot pixel is a pixel that reads high on longer exposures, and can produce white, red, orange, green, or yellow green in longer exposures. The longer the exposure (such as in night photography), the more visible the hot pixels. This phenomenon is caused by the sensor heating up during long exposures. When doing long exposures, use the NOISE REDUCT. option in the menu. When Noise Reduction is enabled, immediately after the initial exposure, the camera makes a second “dark frame” exposure of the same duration with the shutter closed to recreate only the hot pixels in an image. The camera then, in effect, digitally overlays the two images and subtracts the hot pixels in the dark frame image from the original exposure. This doubles the exposure time, so if the original image exposure time was two minutes, the dark frame exposure will be two more minutes for a total time of four minutes.

    Ask Olympus: What is Pixel Mapping?

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