Chromatic Aberration or something else?

Discussion in 'Image Processing' started by barry13, Mar 18, 2015.

  1. barry13

    barry13 Super Moderator; Photon Wrangler

    Mar 7, 2014
    Southern California
    Barry
    Hi,

    This image, and several others of the same bird, have some magenta spots along the bird's back and head.
    I'm guessing it's CA, but neither the E-M1 camera removed it in the JPEG, nor did the CA sliders in RawTherapee...
    The lens is the 40-150mm Pro + MC-14, at 210mm, F/4. The bird was in shade, but the sun was setting 'behind' the bird.

    Is this CA (lateral or longitudinal)? Any good way to remove it?

    85176.

    Thanks!
    Barry
     
  2. sammykhalifa

    sammykhalifa Mu-43 Top Veteran

    762
    Jun 22, 2012
    Pittsburgh PA
    Neil
    Could it be the sun "flaring" off of the sensor? I don't know if that's the proper word or not . . .
     
  3. ManofKent

    ManofKent Hopefully still learning

    789
    Dec 26, 2014
    Faversham, Kent, UK
    Richard
    Odd you'd normally get purple fringing along high contrast areas - white feathers etc. That doesn't seem to be the case here so I'm not sure it's lens aberration.

    As to removing it I can only think of a dropper tool and replacing the colour wiith something more neutral, or going in with a very fine brush at pixel view and cloning/spot healing.
     
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  4. scottz

    scottz Mu-43 Regular

    135
    Jun 18, 2011
    Littleton, CO
    Are you sure it's not feather iridescence?
     
  5. barry13

    barry13 Super Moderator; Photon Wrangler

    Mar 7, 2014
    Southern California
    Barry
    @sammykhalifa@sammykhalifa Hi, I was in full shade, so I don't think it's lens flare.

    Thanks,
    Barry
     
  6. Tilman Paulin

    Tilman Paulin Mu-43 Veteran

    329
    Jun 10, 2013
    Dublin, Ireland
    Moire would be my guess, because of all the fine detail...
    If your raw converter has a tool for that I'd give it a try.
     
  7. barry13

    barry13 Super Moderator; Photon Wrangler

    Mar 7, 2014
    Southern California
    Barry
    I'm not sure. One of the pictures in the series doesn't have it, but if the bird moved, the iridescence could have changed.
    Magenta does seem odd to me on a blue/gray bird, but I suppose it's quite possible.

    I didn't notice it when looking at the bird or through the EVF, btw.

    Thanks!
     
    Last edited: Mar 19, 2015
  8. barry13

    barry13 Super Moderator; Photon Wrangler

    Mar 7, 2014
    Southern California
    Barry
    Searching for 'RawTherapee moire', I found something mentioning possible Bayer filter artifacts causing color shifts:
    http://rawtherapee.com/forum/viewtopic.php?t=2171&start=30
    (in the quote in the first post on that page)

    A DPR thread recommends using the Amaze demosaicing algorithm in RT, but that is already the default.
    Trying other algorithms, or the false-color steps in Amaze, doesn't seem to make a difference.

    Thanks!
     
  9. oldracer

    oldracer Mu-43 All-Pro

    Oct 1, 2010
    USA
    It's not CA. CA doesn't appear in spots and not in other spots. Search the term and read. I think the color is real, whether due to the way the bird is lit or due to that actually being the feather color I don't know. Slim chance but you might check a bird book and see what it says about coloration of this species.
     
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  10. barry13

    barry13 Super Moderator; Photon Wrangler

    Mar 7, 2014
    Southern California
    Barry
    Hi, I saw lots of pics of this bird online, none had any magenta.

    Magenta is a suspicious color as it is red+blue... Could easily be a Bayer filter artifact.

    Barry
     
  11. Tilman Paulin

    Tilman Paulin Mu-43 Veteran

    329
    Jun 10, 2013
    Dublin, Ireland
    It looks like a Western Scrub Jay. They don't have magenta in their feathers.

    Most likely a Bayer filter artifact, as Barry linked to earlier.
     
  12. pellicle

    pellicle Mu-43 All-Pro

    Feb 10, 2010
    Southport, OzTrailEYa
    pellicle
    Is this a 100% section?could be an artifact of moiré , personally I'm struggling to see anything wrong with it.

    If this is cause for complaint then things are very good indeed
     
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  13. barry13

    barry13 Super Moderator; Photon Wrangler

    Mar 7, 2014
    Southern California
    Barry
    Yes, 100% crop, and yes it's a Western Scrub Jay, California subspecies.

    I wasn't complaining, just wondering if there's a way to remove it.

    Thanks,
    Barry
     
  14. Tilman Paulin

    Tilman Paulin Mu-43 Veteran

    329
    Jun 10, 2013
    Dublin, Ireland
    Easiest solution would be some selective colour correction:
    In Photoshop you could use an Hue/Saturation adjustment layer to selectively desaturate magenta (or change it to a different hue).

    In Raw Therapee you should be able to achieve something similar with the HSV Equalizer.
     
    • Informative Informative x 1
  15. pellicle

    pellicle Mu-43 All-Pro

    Feb 10, 2010
    Southport, OzTrailEYa
    pellicle

    Hey Barry, I read after posting your post on the Bayer artifacts. Sorry to answer with the answer alreadyapparent.

    You may find this post interesting

    https://www.onlandscape.co.uk/2010/11/the-mysterious-case-of-the-missing-berries-and-other-stories/

    My turn of phrase was meant to indicate that if there was anything "wrong" with the shot it indicates how high the bar really is. To me the shot was excellent in terms of image quality.

    I think we just need to accept that our tools have limitations after all :)
     
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