Chromatic Aberration Issues

Discussion in 'Digital Photography' started by LumbermanSVO, Dec 10, 2015.

  1. LumbermanSVO macrumors 65816

    Joined:
    Mar 15, 2007
    Location:
    Denton, TX
    #1
    So, my company has a fun new product and I just happened to have it onsite and demo'd it for a customer today. Normally when shooting our products I'm having to deal with refresh rates and moire issues to get a good photo. Today I stumbled upon a whole new issue. Chromatic Aberration...

    [​IMG]

    In this photo, the spherical LED screen has content on it that makes it look like a golf ball with a logo on it, as in, white background. Because of the pixel density, one pixel every 10mm, I am getting severe chromatic aberration around every pixel, making it impossible to shoot. If I use the chromatic aberration sliders in ACR I can almost get the white parts of the sphere back to white, but then I lose color in the logo. The "GoVision" is supposed to be purple, and the "golf" is supposed to be green.

    How would you go about shooting and editing this?

    At the moment my best idea is to go wide with my lens until the individual pixel no longer show up, then crop the photo. Any better ideas?
     
  2. The Bad Guy macrumors 6502a

    The Bad Guy

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    Australia
  3. kenoh macrumors demi-god

    kenoh

    Joined:
    Jul 18, 2008
    Location:
    Glasgow, UK
    #3
    Couple things jump to mind.

    1. Typically stopping lens down as Bad Guy says will remove it.
    2. Maybe try under exposing a stop to stop highlights being blown out and causing CA
    3. Depemding on the light technology, maybe a colour cycle sync problem as the pixels may not be white, they may be a fast cycling RGB and you may be catching it wrong. Try slower or fast shutter speeds to see if you get a different outcome.

    Sorry Clutching at straws I am afraid.
     
  4. chrfr macrumors 603

    Joined:
    Jul 11, 2009
    #4
    That's not so much chromatic aberration as it is a moiré pattern. In short, this is an interaction of the grid of pixels on the sensor and the size of what's in the image. You can reduce or avoid it most easily by changing the distance from the camera to the subject (don't move back then zoom in to fill the frame otherwise you'll have the same problem.) If you have access to a different camera that has a different resolution, it's likely that the same image won't have a problem with that other camera.
    You can also reduce the moiré by using either a separate anti-aliasing filter over the lens or by defocusing slightly. Cameras nearly always have built in anti-aliasing filters but apparently in this case it's not quite enough.
     
  5. Laird Knox macrumors 68000

    Joined:
    Jun 18, 2010
    #5
    It is difficult to tell from that picture (too small). True chromatic aberration is going to be an issue with your lens. Try different lenses and see if one handles it better.

    On the other hand it may be an issue with the PWM as mentioned above. Slow the shutter speed down so that you have enough time to catch the whole sequence. Similar to shooting CRTs and dealing with the scan lines. A static image on the display will work best here.

    Or just send me a display and I will shoot it for you. ;)
     
  6. Policar macrumors 6502a

    Joined:
    Nov 21, 2004
    #6
    Post a bigger picture. You might be describing longitudinal CA, which is more difficult to remove in post than lateral, but even so that's not what the image really looks like... like that's not quite what I see going on.

    You might need to do some photoshop work or composite a few images together.
     
  7. LumbermanSVO thread starter macrumors 65816

    Joined:
    Mar 15, 2007
    Location:
    Denton, TX
    #7
    Well, first of all, I'm thankful that a bunch of MR regulars have jumped in, thanks guys! I've been busy building this kinda stuff, and that's why I haven't posted much in the last 1.5 years.

    Here is a crop of the image, from here you can see that it in a chromatic aberration problem, and not a moire problem:

    [​IMG]

    I took a LOT of shots, all a multiple of the refresh rate of the video screen. Even the shots I took at the same refresh rate (1/60) had the same problem.

    These photos were made with a Canon 550D and Canon 85/1.8 lens. I did a video with my Canon 40/2.8 lens at f/22 and 1/60th and there were still some CA issues on the more extreme edges of the screen.
     
  8. Apple fanboy macrumors P6

    Apple fanboy

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    Feb 21, 2012
    Location:
    Behind the Lens, UK
    #8
    What editing have you done? Both LR and DXO Optics have CA correction.
    Not saying it will make it perfect, but maybe close enough?
     
  9. Berlepsch macrumors 6502

    Berlepsch

    Joined:
    Oct 22, 2007
    #9
    A slightly different idea - as far as I understand, these LED displays use a set of red, green, and blue LEDs for each dot. In other words, the three colors are come from slightly different positions at each dot of the display. So what you think is color aberration of the lens could be just a correct image of this small offset between the LEDs.

    In case of a spherical display there is the extra problem that you see the small panels in the center of the sphere and along the circumference under different angles.

    To test my theory, you could try to make shots with parts of the sphere in different corners of your pictures. In case of CA, the color shifts should be symmetric around the center of the image. If the effect is caused by the LED display itself, the direction of the color shift should not depend on the position in the image.
     
  10. Policar macrumors 6502a

    Joined:
    Nov 21, 2004
    #10
    It doesn't look like chromatic aberration at all. If it were lateral it wouldn't be so severe in the center of the image. If it were longitudinal, the dots in the foreground would be green, not magenta, and stopping down as far as you have would have mitigated it substantially.

    LEDs have unusual spectral distribution and varying color temperature.

    Looking at other products from your company:



    They have a magenta cast, consistent with other daylight balanced LEDs I've used, but more severe. You might want to develop your photo at two different white balance settings then composite the two together.
     
  11. LumbermanSVO thread starter macrumors 65816

    Joined:
    Mar 15, 2007
    Location:
    Denton, TX
    #11
    I just did that and no matter what I did with the color balance, I still got red. Someone at the shop made this photo, I'll have to find out who and what he did differently.

    This is the only display product I've shot where I've had that problem, though the video you posted is interesting. Actually, this is the first time I've shot a screen and had a color problem. Moire problems are much more common with our lower resolution products.
     

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