1. Mick West

    Mick West Administrator Staff Member

    [​IMG]

    The above images are examples of a rolling shutter artifact. A "rolling shutter" means that the image is recorded one row (or column in portrait orientation) at a time, and not simultaneously. This means if the exposure and the flash are of very short duration, then the flash will only illuminate some pixel rows (or columns) of the image. Slowed down it looks a bit like this:
    [​IMG]
    The green rectangle is the rolling shutter window - what the camera sees of the scene at any one time, and it builds up the actual photo by reading from this rectangle. The flash of lighting is very short, but still lights up all the pixels in the rolling shutter window, causing the "beam".

    Here's what's going on in the first image. Notice the beam also shows up in the reflection.
    [​IMG]


    And with the Mayan temple, the lighting is behind the temple, so it only lights up the sky, and not the temple itself. So it looks like the "beam" goes behind the temple.
    [​IMG]

    [​IMG]

    [​IMG]

    This can be replicated with a flash set to strobe, and taking lots of photos or video with an iPhone:

    [​IMG]
    The fact that the "beam" can go "behind" the clouds can seem confusing in a still image. But it's really just that the lightning is behind the clouds, and they are thick enough to block the light. I simulated a similar effect using the flash and a foam pool toy. If the flash is in front of the toy then it illuminates it, and you get the stripe across the toy. If the flash is moved behind the toy, then the toy is not illuminated, so the "beam" (the stripe of the image) looks like it's going behind the toy.


    [​IMG]


    It looks like the flash is not actually working, however you have to remember that for most of the frame, it's actually off. The only time the flash is on is during the white bar.

    In my image the flash gives a white light (as a camera flash is obviously intended to), but lightning often shows up as a purple or pink tinge:
    [​IMG]

    Typical lightning photography with a rolling shutter looks more like half the image being lit by lightning, rather than the column we see above. Here's a more typical lightning shot at night with this problem:
    http://www.productionapprentice.com/tutorials/ccd-vs-cmos/
    [​IMG]

    Notice it's horizontal. The image is scanned one row at a time, but when you take a photo in portrait mode, then those rows are the columns.

    Here I've repeated the flash experiment in a darker setting, and we get the half-illuminated image:
    [​IMG]


    Update Aug 15 2015, a new example:
    [​IMG]
    source, location

    Here the illusion of it being a beam behind the clouds is particularly striking, as a band of dark clouds is partially obscuring the illuminated clouds behind. You can see part of the lightning bolt just below the power lines. Remember it's not actually a beam of light, it's just a slice of a scene as it would look illuminated by lightening.

    This can be especially confusing when you notice the reflection of the "beam" on the hood of the car. Your brain naturally interpret this as a reflection of the scene, and so you think there's actually a beam in the sky. But if you look closely, you'll see the reflection in the hood is actually of a slightly different are of the sky. The "reflection" lines up perfectly vertically, whereas the nearby traffic signals are sloped. If this actually was a reflection of a beam in the sky, then it would also be sloped.

    [​IMG]

    So while it's a reflection of sky illuminated by lighting, it's not the same area of the sky. It's a little unintuitive.

    So again, what we are seeing here is essentially one normal image overlaid with a slice of another image that's illuminate by lighting. (And note that what looks like the reflection of a building in the lower right is actually the reflection of the air conditioning vent inside the car)

    Warning: Complicated Explanation Ahead!

    A very unintuitive topic here is the width of the band. Why does a long exposure (in a dark setting) give a wide band, but the short exposure (in sunlight) give a narrow band? You would think that if the exposure is short, then more of that exposure would be happening during the flash, so the band would be wider.

    The first thing here is that the flash I use only has a duration of 1/5000th of a second (0.2 ms), so if things work the way the previous paragraph suggested, then the most we could illuminate would be a band 1/166th the width of the image (in portrait orientation), and yet we see that we can get half or more of the image illuminated. So what's going on? How can a 1/166th of a frame exposure illuminate half the lines in a frame? And why does it it get narrower for shorter exposures?

    The answer is complicated. CMOS sensors can only be read one line at a time, and yet the exposures can happen simultaneously (or at least overlap). So the reset of each line (the start of when it begins to record) is staggered to match the read-out speed, and the exposure length is actually on an individual line basis.

    The diagram below is showing the "flash window" - i.e. the portion of a frame in which you can fire the flash and have it affect all the rows. Normally when you use the flash, then it's quite dark and so you have a long exposure, and hence quite a big window in which you can fire the flash, If you were to go outside of this window, you'd get the top or the bottom of the image only illuminated by the flash.

    [​IMG]
    Source

    In brighter conditions, the per-line exposures are shorter, so it's more like:
    [​IMG]

    Notice the read-out of the lines (green)is the same angle, as that can't get any faster. This also dictates when the reset (blue) happens. But now that the exposure time (red) is much shorter, only a few lines can get exposed during the flash. Hence the "beam" is narrower for a shorter exposure.

    So the width (or height in landscape) of the beam are actually dependent on three factors
    1. The exposure duration - the red lines above.
    2. The rolling speed - how quickly does the "rolling shutter" move across the sensor. Determined here by read-out speed - the green line.
    3. The flash duration (the yellow bar)
    This gives us a minimum width of the "beam". It's the duration of the flash, divided by the read-out cycle time (i.e. the time between starting two consecutive read-outs). The faster the camera's read-out time, the smaller the potential "beam" and the sharper the edges.

    Why sharp edges? The start and end of the flash might also occur during the reset or read-out phase of the lines, meaning that line only gets partially exposed to the flash. This means the edges of the "beam" are not always sharp.

    The narrowest possible beam comes from a combination of short exposure and short flash. Here I took individual photos in bright sunlight, which gave an Exposure Time of 1/3300. The flash is 0.2ms, or 1/5000 of a second, about 2/3 the duration of a single Exposure time. Here's what we got:
    [​IMG]
    Zoomed in:
    [​IMG]

    So we have a 36 pixel wide beam on a 2488 wide image. There are really lines (as the camera is just rotated 90 degrees). Only half the pixels in the middle are a solid bright color - that would be where the flash fell entirely within the exposure time. The colored pixels on either side indicate where the flash only partially was within the actual exposure time, with the different colors indicating different contributions from the red, green and blue sensors as they are read at out different times.


    For a discussion of Rolling Shutters in SLR cameras, see:
    https://www.metabunk.org/will-an-sl...ts-like-a-beam-of-light-with-lightning.t6718/

    Note: The above post is a summary post from material in the discussion thread below, hence the subsequent discussion might seem somewhat redundant. Updated with the Florida photo on 8/15/2015
     
    Last edited: Aug 30, 2015
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  2. pseacraft

    pseacraft Active Member

    Picture is pretty small but looks like a ray of sunlight that broke through the clouds to me. A larger image would be better...then we could tell if its photoshop...
     
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  3. deirdre

    deirdre Moderator Staff Member

    http://www.pinterest.com/pin/231653974554520462/


    beam.
     
  4. deirdre

    deirdre Moderator Staff Member

    heres a similar pic. and [incorrect] explanation
    Pyramid-Light-Beam.
     
  5. Pete Tar

    Pete Tar Moderator Staff Member

    Naaaaa.
    Why isn't the flare across the whole image, and why does it go behind the jetty in the first one?
     
  6. What I see is some sort of illusion. One would think that if the light source is behind the pier pilon then you would get a shadow on this side of the pilon. Yet the light continues to reflect this side of the pier pilon with no shadow. And without super zoom Mick has it would appear that the joisting and rails of the pier were lit by on the backside of the light source.
     
  7. solrey

    solrey Senior Member

    Here's another where lightning produced the same kind of lens flare.

    http://www.ericteske.com/2012/06/lightning-photographs-produce-crazy.html

    [​IMG]

    EXIF data on Georgies pic looks like it was taken from a phone.

    File Size 67 kB
    File Type JPEG
    MIME Type image/jpeg
    Image Width 640
    Image Height 960
    Encoding Process Baseline DCT, Huffman coding
    Bits Per Sample 8
    Color Components 3
    X Resolution 1
    Y Resolution 1
    YCbCr Sub Sampling YCbCr4:2:0 (2 2)
     
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  8. deirdre

    deirdre Moderator Staff Member

    youre right, it must be the starship enterprise.
     
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  9. pseacraft

    pseacraft Active Member

    I'd like to see the exif data and a high res version but am sure that doesn't exist...I have never had a pic like this of any lightning that I have shot... it could be a lens or sensor artifact..


    Ask and you shall receive...tks solrey
     
  10. Pete Tar

    Pete Tar Moderator Staff Member

    I'm pretty sure that a reflection won't be able to cast a shadow, not the sort of reflection we see in that image anyway because that's more of an optical illusion dependant on the viewer than a real reflected light.

    Can't make out the lighting up of the rails on the pier.

    It looks like a flare, but a flare should obscure over the image, not go behind things.


    It would be worth hearing if it was sighted optically or just showed up in the picture.
     
  11. George B

    George B Extinct but not forgotten Staff Member

    Excellent point about the light column being behind un- distorted items in foreground.
     
  12. deirdre

    deirdre Moderator Staff Member

    the items wouldnt be distorted. I can see the lightning reflected in the water which probably is why the pixel issue continues. the real question is why the pyramid beam stops directly at the pyramid.
     
  13. Pete Tar

    Pete Tar Moderator Staff Member

    But it might be possible, if you take into account what's happening in the pyramid picture above, maybe the flare only happens over things with a certain image value?
     
  14. Pete Tar

    Pete Tar Moderator Staff Member

    Wow, I can't.

    One clue they used in the pyramid pic was


    but I don't know if that works for this picture.
     
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  15. deirdre

    deirdre Moderator Staff Member

    light.
     
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  16. JRBids

    JRBids Senior Member


    I just saw a similar photo on FB except the light was coming out of a pyramid. I'm sure someone else will post the photo, since GMTA.

    Edit. See that :) Deidre did.
     
  17. Pete Tar

    Pete Tar Moderator Staff Member

    Doh. If that beam were physically there then it's reflecting off an imperfect surface, the river, right? So it would be distorted. It's not, therefore, artifact.
     
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  18. deirdre

    deirdre Moderator Staff Member

    I think they mean its a camera artifact. did you message him and ask?
     
  19. The flair seems to be related to the amount of light being emitted by the lightning. the flair seems to dimm as it gets higher in the clouds and dim as it comes closer in the water reflection.
     
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  20. Hama Neggs

    Hama Neggs Senior Member

    I think it's actually seen in front of the land and trees on the far shore and also the jetty. It's just too faint to see very well against those darker colors.
     
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  21. Trigger Hippie

    Trigger Hippie Senior Member


    It's lightning. I can't explain the lens flare effect though.

    beam1.

    EDIT: I made the post without noticing there was an entire third page full of replies. That's the second time I've done this in a week... geez, I'm getting old.
     
    Last edited: Mar 8, 2014
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  22. Last edited by a moderator: Mar 8, 2014
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  23. http://www.nbcnews.com/id/46560621/...show-sign-gods-or-iphone-glitch/#.UxuesvldXbM
     
    Last edited by a moderator: Mar 8, 2014
  24. NoParty

    NoParty Senior Member

    With respect to the Chichen Itza picture, the rule, as I recall
    it from my Intro to Logic course in college went as follows:

    "If accompanying tour guide has not seen such a photo before, it follows that it is the work of Mayan god Kukulkan."
     
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  25. solrey

    solrey Senior Member

    So the image in question was taken with an iphone. Good to know because that points to an artifact peculiar to iphones. I think iphones were used in the pyramid pics but I'm not 100% on that. In my previous post the description of the pic with similar artifacts said they were...


    [​IMG]
     
  26. WeedWhacker

    WeedWhacker Senior Member

    After seeing your comparative picture, dierdre, and explanation, I'm of the mind that this is "case closed".

    Seems there are likely to be more and more such image anomalies in the future, as technology advances, and outpaces the layperson's ability to keep up with all of the details and implications. We can't all be experts in every subject.
     
  27. Mick West

    Mick West Administrator Staff Member

    I believe something like this explanation to be correct, but not "causing an entire column of pixels to offset their values or causing an internal reflection " and I have performed some experiments that shed some light.

    To replace the lightning bolt I used a flash, set to strobe mode, and recorded it with an iPhone 5.
    [​IMG]

    It created a variety of images like:
    [​IMG] [​IMG]

    What we are seeing here with the flash is an artifact of the rolling shutter in the iPhone, and not a column of pixels going bad, or an internal reflection.

    A "rolling shutter" means that the image is scanned one row (or column in portrait orientation) at a time, and not simultaneously. This means if the flash is of very short duration, it will only illuminate some pixel columns of the image. That's what is going on in the OP image:
    [​IMG]

    In my image the flash gives a white light (as it is designed to), but lightning often shows up as a purple or pink tinge:
    [​IMG]

    This is a surprisingly rare artifact, as it requires a brief lightning bolt to occur either entirely in the reset or read-out portion of the exposure, both of which are very short. To duplicate it I had to use a high speed strobe in sunlight to get the flash at the right time

    Typical lightning photography with a rolling shutter looks more like half the image being lit by lightning, rather than the column we see above. Here's a more typical lighting shot at night with this problem:
    http://www.productionapprentice.com/tutorials/ccd-vs-cmos/
    [​IMG]

    Notice it's horizontal. The image is scanned one row at a time, but when you take a photo in portrait mode, then those rows are the columns.

    Here I've repeated the flash experiment in a darker setting, and we get the half-illuminated image:
    [​IMG]


    This video demonstrates what is going on with a rolling shutter, although it's a little misleading as it assumes the reset and read-out phases are happening simultaneously.
     
    Last edited: Mar 9, 2014
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  28. Mick West

    Mick West Administrator Staff Member

    Oops, I split the thread without realizing there was another page! I shall merge and reword.
     
  29. Pete Tar

    Pete Tar Moderator Staff Member

    Can you replicate it appearing behind darker objects?
     
  30. Mick West

    Mick West Administrator Staff Member

    Yes, although hard to replicate the circumstances perfectly. Here I'm holding my flash behind a leather armchair (see my hand at the bottom left)
    [​IMG]

    It's going "behind" the pyramid because what you are seeing is the sky being lit up by the flash. The foreground is dark and facing away from the lighting, so is hardly lit. The OP image has the reflection of the sky.
     
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  31. WeedWhacker

    WeedWhacker Senior Member

    As a long-time Trekker...I fear I must disagree. The color of the Phaser beam is inconsistent with Federation technology.

    ( :) )
     
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  32. It must be romulan then
     
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  33. Mick West

    Mick West Administrator Staff Member

    It's not unique to iPhones, it would happen with any camera using a rolling shutter.
     
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  34. Pete Tar

    Pete Tar Moderator Staff Member

    Perhaps a better way to demonstrate the obscuring would be with the rungs of a ladder?
     
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  35. Mick West

    Mick West Administrator Staff Member

    [​IMG]
     
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  36. Mick West

    Mick West Administrator Staff Member

    Here's a better illustration now it's bright enough. Two photos, one with the light source in front of the chair, and one behind:

    [​IMG]
     
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  37. Mark Barrington

    Mark Barrington Active Member

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  38. Mick West

    Mick West Administrator Staff Member

    The lack of a physical shutter is not why they use a rolling shutter. It's because they use CMOS sensors, rather than CCD, as CMOS is better for battery life, and easier for a slow phone to process. They could use CCD (or a more expensive type of CMOS) with a global ("total" in your article) digital shutter.

    [Edit: although rereading that, maybe you were saying that normally you need a physical shutter for rolling shutter sensors to work well? Either way, they use a rolling shutter because of cost]
     
    Last edited: Mar 9, 2014
  39. Mark Barrington

    Mark Barrington Active Member

    Yeah, in the old days of film photography, the difference was between a shutter curtain that was typically used on 35mm SLR cameras which used a rolling shutter and a leaf type shutter which was usually incorporated in the lens for most larger format cameras. I have used medium format cameras that used either technology. In any case, it's an artifact that would be familiar to photographers before the advent of digital photography. I was just commenting on it being called 'rolling shutter' since there's no physical shutter. For digital cameras, the 'shutter' is the interval between a pixel on the sensor starting and ending data collection.

    Edit: Here's the Wikipedia article about focal plane shutters (we allways called them shutter curtains, but they were often made of metal). It mentions some of the motion and flash effects caused by rolling shutter: http://en.wikipedia.org/wiki/Focal_plane_shutter
     
    Last edited: Mar 9, 2014
  40. Mick West

    Mick West Administrator Staff Member

    Interesting, I didn't think of it as a film artifact, but of course effectively the shutter of a camera "scans" over the frame in a similar way to a rolling digital shutter. Here's what a Film SLR shutter looks like in slow motion:

    And the same on a digital SLR:

    Note at 1/1000th, the exposure is a slit that "rolls" over the frame.

    For a film SLR the process is:
    1. Shutter opening, partial exposure
    2. Shutter fully open, full exposure
    3. Shutter closing, partial exposure
    So if the flash happens during 1 or 3, then you will get a partial-frame illumination. And the faster the shutter speed, the less time is spend in #1, so the more likely a sync problem is.

    For a digital SLR, you have the fast physical shutter, and you also have a slow digital rolling shutter. But the physical shutter covers the digital rolling (which happens before and after the physical shutter), so you only see digital rolling artifacts on a digital SLR when it is taking video (where the physical shutter is always open). The photo process is:
    1. Roll shutter reset, so some lines are capturing, but the physical shutter is closed, so dark
    2. Physical shutter opening, partial exposure
    3. Shutter fully open, full exposure
    4. Shutter closing, partial exposure
    5. Roll shutter read. Some lines capturing, but again, it's dark.
    So the effect is identical to a film SLR

    With a phone camera, you only have the digital rolling shutter, so you get the artifacts in photos. The process being:

    1. Rolling reset start
    2. Pause
    3. Rolling read start
    4. Wait for read to finish
    Which is highly unintuitive, and difficult to explain.
     
    Last edited: Aug 16, 2015
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