What do you think this is? Rolling shutter issue? - Page 2 at DVinfo.net

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Old December 10th, 2007, 05:52 AM   #16
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Originally Posted by Leonard Levy View Post
Sorry I just don't seee anything. maybe i'm looking in the worng place.
Those are my feelings as well. There's a limit to the number of conclusions you can draw from a video clip posted on the web, but this clip does seem very clean, noise free, and crisp, and better than I'd have expected from any previous camera in this class.

I can't see any motion related problems that aren't caused by camera movement and/or focus shifting. But maybe it's because of looking in the wrong place?
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Old December 10th, 2007, 06:21 AM   #17
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Diffraction!

Hello Kaku

I guess that your problem is the geometric distortion of the number 87-39, is it right?

If my guess is right, I just succeeded to reproduce such a geometric distortion with my EX1, and also with my XH A1 too. It can be explained by the diffraction, as Pasty already explained. My experiments are as follows: The focal length is abount 10m, and an obstacle very near the aperture. If the obstacle moves, the distortion changes, but for stationary obstacle, the distortion freezes. Thanks.
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Old December 10th, 2007, 07:06 AM   #18
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It's diffraction.
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Old December 10th, 2007, 07:13 AM   #19
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Diffraction

Took me a few replays to spot the 'distortion' (easier when dragging the head frame-by-frame), but have to say I third (fourth?) the diffraction opinion... looks to me to be just plain ol' laws of physics/optics at work.

Can't blame a camera for behaving like that ;0)
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Old December 10th, 2007, 09:07 AM   #20
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Took me a few replays to spot the 'distortion' (easier when dragging the head frame-by-frame), but have to say I third (fourth?) the diffraction opinion...
Ah! I see what you're getting at. I'm not sure diffraction is quite the right term though. If you frame by frame it with a horizontal edge held by the image of the plate on the screen, the shape of the plate doesn't really change - what does happen is that it gets differentially shaded by the out of focus man, which I agree at normal speed does seem to give the illusion of distortion.

Quite easy to simulate without a camera - look at some writing about 3 feet away with one eye closed, and move your finger back and forth past the opened eye very close. Not a rolling shutter effect, just optics!

And under those lighting conditions, the pictures still look very, very good......
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Old December 10th, 2007, 09:46 AM   #21
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Originally Posted by David Heath View Post
Ah! I see what you're getting at. I'm not sure diffraction is quite the right term though. If you frame by frame it with a horizontal edge held by the image of the plate on the screen, the shape of the plate doesn't really change - what does happen is that it gets differentially shaded by the out of focus man, which I agree at normal speed does seem to give the illusion of distortion.

Quite easy to simulate without a camera - look at some writing about 3 feet away with one eye closed, and move your finger back and forth past the opened eye very close. Not a rolling shutter effect, just optics!

And under those lighting conditions, the pictures still look very, very good......
Oh, David, I can see distortion of several pixels! it really moves and is distorted. You can see the movement (or distortion : depends on the obstacle's shape) by your 'eye emulation' also.
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Old December 10th, 2007, 11:06 AM   #22
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Originally Posted by Mooho Bae View Post
it really moves and is distorted. You can see the movement (or distortion : depends on the obstacle's shape) by your 'eye emulation' also.
Glad you got the "eye emulator" to work! What I think is happening is that the finger is is obstructing different parts of the iris with respect to different parts of the image over a narrow band. Over that band the effective f stop varies from max (not obstructed) to very small (nearly all obscured), and if you deliberately defocus the eye, you can see the sharpness of the writing vary over that band - the depth of field is effectively being varied over the relevant area. This is very clearly happening if you go between three frames on Kakus footage - where the "39" first appears it's sharp (and partially obstructed) but the "87" isn't, then in the next frame it becomes equally unsharp compared to "87" as the person moves by.

The other thing that is happening is that the effective centre of the iris moves as it is obscured from one direction, which may well shift the image slightly.

This effect would be expected to be most prominent at large apertures - and in this night scene (which doesn't look like any gain was used) a large aperture is likely to be exactly what was used.

It can all be predicted with assuming light rays travel in straight lines, which is why I don't think "diffraction" is the right term to use to explain it. Diffraction applies to effects which can only be explained by thinking of light as a wave motion.
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Old December 10th, 2007, 11:54 AM   #23
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yes as many people have mentioned, this is definitely not a rolling shutter or compression artifact. this would happen with any lens on any camera. i see this happen with my eyes all the time. anyone who has pretended to squish other people's heads with their fingers from a distance knows this. objects deform and wrap around your out of focus finger just as it begins to cover up the object from being visible to your eye.

too bad this camera has such shallow depth of field. if only they would come out with a deep depth of field camera so we wouldnt have to deal with issues like this. and that high sensitivity! what are we supposed to do with all our powerful lighting equipment! now we have to worry about blown highlights at night, too??

man i want an EX1
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Old December 10th, 2007, 08:02 PM   #24
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It's easy to nit-pick when looking for faults, but conclusions can be taken only from well setup tests. In this case the taxi has just stopped moving (has it?) and we see the stop lights activated a couple of times. People are walking across acting as stops in terms of image intensity, which affects flaring in the image. Light is not bending around people (remember your school diffraction physics about the influence of scale and the wavelength of light). I think, with all due respect, we can hear an echo of that saying "Move along folks, nothing to see here".
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Old December 11th, 2007, 05:20 AM   #25
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Light is not bending around people (remember your school diffraction physics about the influence of scale and the wavelength of light). I think, with all due respect, we can hear an echo of that saying "Move along folks, nothing to see here".
Serena, as far as I know, the geometric Optics was generalized by the Fourier Optics which is based on 'diffraction' and Huygens' principle. IMHO, The image distortion discussed here can well be expressed by the Fourier optics, and I'm sure the ray 'looks' bending near the obstacle in this case. Not only the ray bends, the obstacle also acts as some lens in this case. Without the obstacle, the Taxi number 9 is so blurred that we can not recognize it. But when the bag is very close to the number 9 (not physically close, but close to the ray), we can clearly recognize '9'. All these phenomena can be explained by the Fourier Optics, based on the 'diffraction', IMHO.

I'm not sure this helps...
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Old December 11th, 2007, 05:43 AM   #26
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I reckon I'll leave it there; reading on the subject is readily available.
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Old December 11th, 2007, 06:55 AM   #27
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Originally Posted by Mooho Bae View Post
Without the obstacle, the Taxi number 9 is so blurred that we can not recognize it. But when the bag is very close to the number 9 (not physically close, but close to the ray), we can clearly recognize '9'. All these phenomena can be explained by the Fourier Optics, based on the 'diffraction', IMHO..
Yes, but I think it's simpler than that, and based on larger geometries than are applicable for diffraction related effects.

The 9 appears sharp in the one frame because the partial obstruction of it by the bag effectively means that only part of the lens is used to image it, so effectively the lens is a smaller aperture for that part of the image. Hence greater depth of field, so it appears sharper (and somewhat darker). Try drawing ray diagrams to represent what happens frame to frame.

But we do all seemed agreed that it's an optical effect, and nothing to do with anything inherent any particular camera.
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Old December 11th, 2007, 07:07 AM   #28
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Yes, but I think it's simpler than that, and based on larger geometries than are applicable for diffraction related effects.

The 9 appears sharp in the one frame because the partial obstruction of it by the bag effectively means that only part of the lens is used to image it, so effectively the lens is a smaller aperture for that part of the image. Hence greater depth of field, so it appears sharper (and somewhat darker). Try drawing ray diagrams to represent what happens frame to frame.

But we do all seemed agreed that it's an optical effect, and nothing to do with anything inherent any particular camera.
David,

I totally agree with your final sentence. Further discussion looks meaningless IMO, but I want to say just one thing : Your 'small aperture model' will result in image sharpen over large area, but in actual case, the resolution change occurs in very near vicinity of the obstacle.
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Old December 11th, 2007, 07:39 AM   #29
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Your 'small aperture model' will result in image sharpen over large area, but in actual case, the resolution change occurs in very near vicinity of the obstacle.
I disagree - if we assume an iris diameter of 1 inch, the obscuring object 10 feet away, and the object being imaged 60 feet beyond that, then the affected region of the object will be 6 inches wide. To one side of that the image will be totally obscured, to the other side totally clear - rays from that part of the image will be received by all parts of the lens.

But for that 6 inch strip of the image, rays will only be accepted by part of the lens - effectively a smaller diameter iris and greater depth of field.
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Old December 11th, 2007, 08:11 AM   #30
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I disagree - if we assume an iris diameter of 1 inch, the obscuring object 10 feet away, and the object being imaged 60 feet beyond that, then the affected region of the object will be 6 inches wide. To one side of that the image will be totally obscured, to the other side totally clear - rays from that part of the image will be received by all parts of the lens.

But for that 6 inch strip of the image, rays will only be accepted by part of the lens - effectively a smaller diameter iris and greater depth of field.
Oh, David, thank you for nice explanation. It is interesting. Up to now, I have thought the iris just on to the aperture. The fundamental theory of the Fourier Optics I remenber is the relationship between focal plane and the aperture plane.

But, still, I can't imagine the geometric distortion explained by your small aperture, ray tracing model. IMO, the diffraction will be the key in this issue.
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