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Is this sensor noise, black becomes blue/purple ??

Discussion in 'Olympus Cameras' started by Tinderbox (UK), Nov 1, 2014.

  1. Tinderbox (UK)

    Tinderbox (UK) Mu-43 Regular

    This is an extreme version, i have high iso photo`s that the black becomes blue/purple when i increase the exposure in PS

    Have a look at the photo in the link below, you can see the blue/puple in that raw without increasing the exposure at all, and the flash was not used.

    Is there a way to remove this blue/purple colour so i can still increase the exposure without it showing.

    http://www.filedropper.com/pb0100091

    Thanks

    John.
     
  2. Amin Sabet

    Amin Sabet Administrator

    Apr 10, 2009
    Boston, MA (USA)
    I was unable to download the file, but what you describe sounds like sensor noise. There are various ways to deal with it including selectively desaturating the color in that area or changing the black point to block it out.
     
  3. tosvus

    tosvus Mu-43 Top Veteran

    632
    Jan 4, 2014
    You should have a way in lightroom or adobe raw to increase noise reduction on color. There is also a noise reduction setting for luma, but the color is the one to use to deal with your issue.
     
  4. Tinderbox (UK)

    Tinderbox (UK) Mu-43 Regular

    This is just a dirty cut and paste.

    [​IMG]

    Here is a better photo

    PB010032_zps43fdb1dd.
     
  5. Tinderbox (UK)

    Tinderbox (UK) Mu-43 Regular

    I have noiseware professional plugin in PS and i have used luma and colour but it does not remove it.

    John.

     
  6. kwalsh

    kwalsh Mu-43 Top Veteran

    775
    Mar 3, 2012
    Baltimore, MD
    It's sensor noise. That's underexposed ISO6400 on the tiny little Stylus 1 sensor - so not surprising.

    I can get rid of most of it in LR/ACR by moving the color NR slider up to about 50 at which point some purple remains in some shadow patches. To get rid of those dark purple areas just clip the blacks using the tone curve - drag the lower left corner to the right to push the shadows to pure black.
     
  7. Tinderbox (UK)

    Tinderbox (UK) Mu-43 Regular

    I have seen this happen with the EM5 at very high iso and it had bad horizontal banding in raw samples in a online review.

    Sorry i dont have LR only PS CC

    John.

     
  8. Klorenzo

    Klorenzo Mu-43 All-Pro

    Mar 10, 2014
    Lorenzo
    This is the best I could get after a few experiments with Darktable: https://www.dropbox.com/s/jtk4gqjrsvk8rls/darktable_exported.zip?dl=0

    A lot of base raw denoise, two extra passes of chroma denoise (equalizer and non-local) and luma denoise to smooth it all.
    I had to play with the demosaic parameters (color smoothing) to get rid of the purple patches.
     
    • Like Like x 1
  9. tosvus

    tosvus Mu-43 Top Veteran

    632
    Jan 4, 2014
    When you open a Raw file in Photoshop, you should get the camera raw dialog. Underneath the histogram, there are a bunch of tabs. The third one deals with Sharpening and Noise Reduction. When you click that, in the bottom part underneath the tabs you will see Luminance (strength is the first parameter, then detail and contrast). Below that you see Color (again, strength is the first one to play with, which is just labeled Color. It will typically on my camera default to 25, you probably have to go a good bit higher, if very dark, plus small sensor camera.

    Edit: Opened yours, and just some quick fiddling with those settings won't save this one. I think you would have to do some manual corrections in areas, or get a more powerful denoiser with more settings to tweak.
     
    • Like Like x 1
  10. kwalsh

    kwalsh Mu-43 Top Veteran

    775
    Mar 3, 2012
    Baltimore, MD
    PS CC would include ACR which has identical controls to LR.
     
  11. Tinderbox (UK)

    Tinderbox (UK) Mu-43 Regular

    Hi.

    I tried PS ARC and it does nothing to the colour noise.

    thanks

    John.
     
  12. Klorenzo

    Klorenzo Mu-43 All-Pro

    Mar 10, 2014
    Lorenzo
    Are you sure you are you need to remove chroma noise? In the sample you posted I can see none:

    luma-e-chroma-noise1.

    This is what I see as base image from the raw file (lot of chroma noise):

    img_0001_base_crop.

    and this is what I got with my last attempt: fixed exposure, white balance, added fine local contrast to boost details, added a luma equalizer to polish the smaller grain. I do not why but I love to denoise images :)

    img_0001f_crop.

    Full file and darktable edit file: https://www.dropbox.com/s/tcc2ejsg8vvuud1/darktable_exported2.zip?dl=0

    One hint that should be valid for any program: turn off the sharpening or rise the sharpening threshold a lot to avoid to enhance the noise too.
     
    • Like Like x 1
  13. Tinderbox (UK)

    Tinderbox (UK) Mu-43 Regular

    I am not bothered about the noise, it`s the blacks becoming blue/purple as i have outlined in the photo below, i have tried all the advice i have received and only reducing the exposure gets it back to black but that makes the photo too dark.

    EDIT : I just had a look at the last photo you posted, how did you get the blacks to stay black when the exposure is increased?

    John.

     
  14. hazwing

    hazwing Mu-43 All-Pro

    Nov 25, 2012
    Australia
    I think you are pushing the limits of what the sensor is capable of. The image is taken at high ISO and you are increasing the exposure further? I think it's not unusual to get colour shifts, in that situation.

    Things you could try, but might have limited success
    -reduce the black point
    -in HSL - reduce the luminance of blue and purple
    -brush negative exposure on the areas you want to black
    -add an 'artsy filter' to purposely make everything look blue/purple/vintage :p

    Or better yet, retake the photo with better lighting.
     
  15. Tinderbox (UK)

    Tinderbox (UK) Mu-43 Regular

    Some times you have to choose between a blurred image due to low shutter speed or image noise due to high iso, the image noise is easier to deal with, i dont expect to be doing this regularly.

    John.
     
  16. hazwing

    hazwing Mu-43 All-Pro

    Nov 25, 2012
    Australia
    Hows this for comparison? I increase the exposure of your original file to +1.3 EV to get it to a similar brightness to yours

    Then proceeded to do the first two points in lightroom.
     

    Attached Files:

    • Like Like x 1
  17. Tinderbox (UK)

    Tinderbox (UK) Mu-43 Regular

    That looks great, the blacks are black and the photo is reasonably bright.

    You just need to write a easy guide so i can do the same :biggrin:

    John
     
  18. Klorenzo

    Klorenzo Mu-43 All-Pro

    Mar 10, 2014
    Lorenzo
    How much did you rise the exposure? I find out that as soon as I go over +1 EV black areas start to turn to purple. +1.3 EV is the maximum I can go with the base image.
    Moving up the black point helps to contain the purple patches.

    In my previous picture I rised the exposure of only +0.15 EV and then used the Tone curve to get the brightness I wanted. I can go up to +0.80 with no problems.
     
  19. hazwing

    hazwing Mu-43 All-Pro

    Nov 25, 2012
    Australia
    I think what I've done works okay with this photo, because the subject of interest does not have much blue or purple to it. My edit's have been done in lightroom because that's what I am more familiar with. I don't have photoshop, but I would assume you could do something similar.

    First I pushed the exposure +1.30EV until it seemed similar to what you have posted. In lightroom there is a tab for adjusting the HSL (hue/saturation/luminance) of the various colour channels. I have reduced the luminance of blue and purple colours (in this photo -100 in these channels). This makes anything blue or purple darker. You could also reduce saturation of these colour channels as well.

    I then reduce the black point slider until it seemed sorta right. I arbitarily chose -50 on this image. You tend to find as you reduce the black point, the image might darken slightly, and you might be tempted to raise EV again.

    If your subject had a lot of blue or purple to it, your probably won't want to use HSL tab. Instead you could try apply negative exposure to the select regions you want to darken. As you darken these areas, the purple/blue colour shift should reduce.