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Image distortion, again.
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4233 52 2020-1-5
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Mgozer
First Officer
Italy
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Hi everyone.
A couple of days ago I received back my Mavic Mini from the European repair center; it was sent them because of the image distortion it was producing (it can be seen here:
https://forum.dji.com/forum.php?mod=viewthread&tid=203430#pid2027375).
Dji was really kind to send me a new drone, but as I just started to test it, it looks to me that it suffers from the very same issue the old one had.
Now, in order to understand if it is faulty as the first one, I'm trying to better show the issue I identified and I'd like the community members to perform the very same test.

The test is very simple indeed:
-holding the drone (no need to make it hover), tilt the camera full down and enable the central cross and the 3/4 view in the camera advance settings.
-look for a floor having squares or a straight geometric pattern and take a picture of it with the drone, centering the cross to a crossing point of the pattern.

Here it follows some picture of my test and, the last one, a tentative to highligh (using the poor's man paint) the lines.

If your Mavic Mini does not produce such a distortion (it looks a double distortion; barrel at the edges and punch in the middle), then I'll have to send the drone back again, but if it is a common issue, then it can be fixed by the firmware I guess.

Thanks everyone will help.
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2020-1-5
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droneTO
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Canada
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I'm not sure that this would be an issue, since it's normal to have such distortion on wide angle lenses. It can be corrected in post, or with firmware in camera sometimes.

Have you seen go-pro footage? DSLRs with lenses 16mm and less, will exhibit this as well and are typically adjusted in post.
2020-1-5
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ARTPiranha
First Officer
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Russia
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Its normal! Is it your first drone?
2020-1-5
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Mgozer
First Officer
Italy
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ARTPiranha Posted at 1-5 08:50
Its normal! Is it your first drone?

No, I had a Parrot Bebop 2 before, now I have a Mavic Pro and the Mavic Mini.
I also have the Osmo Pocket, for what is concerned.

None, among the Bebop 2, the Mavic Pro or the Osmo Pocket, show this behaviour.
2020-1-5
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Mgozer
First Officer
Italy
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droneTO Posted at 1-5 08:39
I'm not sure that this would be an issue, since it's normal to have such distortion on wide angle lenses. It can be corrected in post, or with firmware in camera sometimes.

Have you seen go-pro footage? DSLRs with lenses 16mm and less, will exhibit this as well and are typically adjusted in post.

Yes I know about the wide angle distortion, but this is something different.
Please look at the center of the images, there is a pincushion distortion and, at the edges, a barrel distortion.

2020-1-5
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jonny007
Captain
Germany
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Do you really see that as an issue that you want to send the drone back?  So I would not notice that because I never take pictures of tiles and you cannot see such "distortions" on "normal" pictures. But the next time the drone's camera is on, I'll take a picture of the tiles in the bathroom to check. :-)
2020-1-5
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Mgozer
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jonny007 Posted at 1-5 12:14
Do you really see that as an issue that you want to send the drone back?  So I would not notice that because I never take pictures of tiles and you cannot see such "distortions" on "normal" pictures. But the next time the drone's camera is on, I'll take a picture of the tiles in the bathroom to check. :-)

In static picture this is not an issue at all, of course, but in moving videos, when you have geometric objects, like walls or buildings, you will notice the issue with a little bit of attention.Anyway, of course I don't usually take picture of the tiles, like nobody does, but this was just for test.
I repeat again that my intention is just to understand if this distortion is normal on the Mavic Mini or not, that's it.
Thanks for your help.

2020-1-5
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Geebax
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Mgozer Posted at 1-5 12:17
In static picture this is not an issue at all, of course, but in moving videos, when you have geometric objects, like walls or buildings, you will notice the issue with a little bit of attention.Anyway, of course I don't usually take picture of the tiles, like nobody does, but this was just for test.
I repeat again that my intention is just to understand if this distortion is normal on the Mavic Mini or not, that's it.
Thanks for your help.

OK, if that is your aim, then yes, it is normal. Considering the cost of the drone, the camera part is about $50 worth, and you cannot expect good lens geometry at that price.
2020-1-5
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42Neil
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Interesting.  As you are probably aware, most/all lenses have some level of distortion inherent to their design.  Wide angle lenses (and especially wide lenses with simple optical designs) are particularly prone to such distortion.

The most common kind of distortions are barrel or pincushion distortions, but there is also another known as "mustache" distortion which is a wavy looking distortion, typically exhibiting barrel distortion in the centre and pincushion distortion towards the edges.  However, this is the opposite of what your example shows (which shows pincushion distortion in the centre and barrel distortion at the edges).

It is pretty common practice these days for software distortion corrections to be applied in camera (to the jpegs and video footage).  Therefore my guess would be that the Mavic mini lens has inherent moustache distortion, that is being slightly "overcorrected" in your copy (both of your copies in fact).  As you say it would be useful to get some more examples from other users.  If all of them show this slight overcorrection, it is possibly something that DJI could address in a firmware update.

Either that or you need a better tiler.

N.B.  Interestingly, I would check the distortion of mine, but I have sent is back for replacement due to a "ripple" effect that I noticed in the video footage (noticed towards the corners).  I did wonder whether if that  issue could be related to lens distortion / software distortion correction, or possibly a software stabilisation effect.  Once I get my replacement I will do some more testing.
2020-1-5
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Mgozer
First Officer
Italy
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Thanks you all.
I look forward your tests.
This could help all of us.
2020-1-5
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jonny007
Captain
Germany
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Ok, if you hadn't said that, I would never have noticed it, not with a single picture or video. Perhaps not an optimal "test environment" in my bathroom, because the tiles are not so small and on the right side the bathtube disturbs, but in the (left) corners you see a "little kind" of distortion. In the middle? Perhaps, perhaps not ... mmh.
2020-1-5
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WrongWay Feldman
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In what world is that even a problem?
2020-1-5
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Mgozer
First Officer
Italy
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jonny007 Posted at 1-5 13:33
Ok, if you hadn't said that, I would never have noticed it, not with a single picture or video. Perhaps not an optimal "test environment" in my bathroom, because the tiles are not so small and on the right side the bathtube disturbs, but in the (left) corners you see a "little kind" of distortion. In the middle? Perhaps, perhaps not ... mmh.[view_image]

thanks a lot; i see the very same distortion of mine.
I'll post a video showing this could be a problem.
2020-1-5
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Mgozer
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Here follows a test video showing a situation when this distortion can lead to an unpleasant result (it is easy to spot the deformation at the bottom side)


Suppose I want to film sideway a moving subject... each time a staight object will get into the shot, it will be affected by this effect.
I understand this could take place very rarely, so it is not such a huge problem.

Anyway, if we understand that this is as per specifications, maybe DJI can better tune-in the image geometry in the next firmware.
2020-1-6
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AntDX316
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If they made it where there would be no distortion, that would take going over the 250g limit.  They've cut down on the proper parts where it compromises flight reliability and increases barrel distortion.
2020-1-6
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izotop
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WrongWay Feldman Posted at 1-5 13:51
In what world is that even a problem?

in many worlds, but for general amateur use, not that much. m2p have it too, but it is auto-corrected (where you loose a bot of field of view), if correct video mode is used, otherwise it have to be done in post.
2020-1-6
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SupBro
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Looks more artistic to me!
2020-1-6
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Mgozer
First Officer
Italy
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Anyone else could find this distortion in his/her own Mavic Mini?
2020-1-6
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jonny007
Captain
Germany
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@Mgozer : I had to watch the video several times to discover the "distortion". For me, I can say that it doesn't bother the recordings I make, but let's say : It would certainly not be a disadvantage if the problem could be fixed.
2020-1-6
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42Neil
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I just tested mine and it definitely shows the same characteristics, i.e. slight pincushion distortion in the centre and barrel distortion at the edges.

My tiles are i bit large unfortunately, but you can still make out the overall characteristic.

2020-1-6
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droneTO
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Mgozer Posted at 1-5 11:42
Yes I know about the wide angle distortion, but this is something different.
Please look at the center of the images, there is a pincushion distortion and, at the edges, a barrel distortion.

You're right, it is odd, and is very apparent in your video example.

I will test mine shortly - I haven't noticed so far in normal flying, but didn't film anything up close specifically...
2020-1-6
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Geebax
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AntDX316 Posted at 1-6 02:59
If they made it where there would be no distortion, that would take going over the 250g limit.  They've cut down on the proper parts where it compromises flight reliability and increases barrel distortion.

(Almost) never has more rubbish been written by one person.
2020-1-6
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Matthew Dobrski
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Geebax Posted at 1-6 20:45
(Almost) never has more rubbish been written by one person.

Right, almost never ... A few noteworthy competitors appeared recently on this forum ...
2020-1-6
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AntDX316
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Geebax Posted at 1-6 20:45
(Almost) never has more rubbish been written by one person.

What is your explanation then?
2020-1-6
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Geebax
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AntDX316 Posted at 1-6 23:19
What is your explanation then?

Go away, I don't talk to idiots.
2020-1-6
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Mgozer
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42Neil Posted at 1-6 12:37
I just tested mine and it definitely shows the same characteristics, i.e. slight pincushion distortion in the centre and barrel distortion at the edges.

My tiles are i bit large unfortunately, but you can still make out the overall characteristic.

Thanks for your test, I really appreciate it.

It looks like that yours shows the very same image geometry.
Now I almost think this could be as intended, then, if so, it can definitively tuned by firmware.
2020-1-7
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Ice_2k
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this lens characteristic is usually corrected when recording on bigger drones but perhaps the Mini simply doesn't have the firepower to do this on the go. A similar issue is with the M2P when filming in 10bit D-Log. It can correct this lens effect in all other modes except this one. Because it's encoding with H265 it simply doesn't have the processing power to do it on the go. It can easily be corrected in post though.
2020-1-7
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42Neil
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My suspicion is that what we are seeing *is* already distortion corrected in the mini (as I would expect a cheap, simple lens design to have distortion worse than this if it were completely uncorrected).

I think they have just slightly got the corrections slightly wrong and have slightly over-corrected the centre.  Ironically, if they had applied no corrections at all it would likely be easier to fix in post, as wavy distortion is trickier to fix than just simple barrel distortion.

As others have said, this kind of distortion probably wont be a problem for many/most subjects, but for subjects with a lot of straight lines (such as architecture or very straight roads or horizons) it can be quite distracting, as shown in the OPs example video.
2020-1-7
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Mgozer
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42Neil Posted at 1-7 06:43
My suspicion is that what we are seeing *is* already distortion corrected in the mini (as I would expect a cheap, simple lens design to have distortion worse than this if it were completely uncorrected).

I think they have just slightly got the corrections slightly wrong and have slightly over-corrected the centre.  Ironically, if they had applied no corrections at all it would likely be easier to fix in post, as wavy distortion is trickier to fix than just simple barrel distortion.

I agree.
That's why I hope DJI could better tune it.

P.S.
I'm glad you got your drone back
2020-1-7
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42Neil
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Mgozer Posted at 1-7 06:54
I agree.
That's why I hope DJI could better tune it.

Thanks.  My replacement seems to have resolved the ripple/wobble issue i had with my first copy, which i was even more distracting than the distortion.
2020-1-7
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DJI Mindy
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Hi Mgozer, this minor distortion is within normal range, our engineers will keep optimizing its performance via the firmware upgrade, please note the future update. Thank you.
2020-1-13
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Mgozer
First Officer
Switzerland
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DJI Mindy Posted at 1-13 00:34
Hi Mgozer, this minor distortion is within normal range, our engineers will keep optimizing its performance via the firmware upgrade, please note the future update. Thank you.

Thanks for the reply Mindy.
I look forward the next update hoping for a better tuned image geometry.

2020-1-14
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InspektorGadjet
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All cameras suffer from this, that is why there are "lense profiles" which correct them.
Correcting that in the drone would crop the image and add unnecessary extra processing, better done in post.
I believe the camera from the Osmo pocket has same distortion, so if there are presets for the Osmo it could be applied to mavic mini too.
2020-1-14
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denesberky
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RE: Image distortion, again.

Hi everyone

I just noticed this on my new Mavic Mini after a few shots and in some of them it is very unfortunate.
Here you can see how a trains moves like a snake on the video.

https://www.youtube.com/watch?v=h2GgLGeDzuY&feature=youtu.be

Hope this can be somehow adressed. I mean a straight line in reality should be a straight line on the video as well...
Until then, is there an easy way to correct this?
2020-3-15
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Corger
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denesberky Posted at 3-15 08:26
Hi everyone

I just noticed this on my new Mavic Mini after a few shots and in some of them it is very unfortunate.

The straight lines of the railroad and movement of the train accentuate the distortion; that's unfortunate.

I took a picture of a grid pattern and I have similar distortion on my Mini.  I never noticed the up and down distortion at the bottom until now.

Maybe DJI can release some lens correction presets for the Mavic Mini.
2020-3-15
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Mgozer
First Officer
Italy
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denesberky Posted at 3-15 08:26
Hi everyone

I just noticed this on my new Mavic Mini after a few shots and in some of them it is very unfortunate.

Even if a lot of users here doesn't bother or doesn't see this issue at all, it is very noticeable indeed.
DJI is aware of that and I'm confident they are working on a fix.
2020-3-16
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Murchx
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Hi! Same problem to my Mavic Mini (fly more combo, EU, 2019/11). Reported this issue to DJI support - they told (december 6th) this is caused by distortion correction algorithm and will be optimized in the future firmware update. But to me looks not every Mavic Mini has this problem. Can't wait for magic firmware update.

image distortion

image distortion

2020-3-18
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Mgozer
First Officer
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It looks to me that this issue is wide spread and there is no Mavic Mini not affected. It is as per specification.
Sometimes it is noticeable, sometimes not, it only depends on the shot.
The last one posted here is very visible.
The good news is that it is fixable via firmware and I look forward to it.
2020-3-19
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Murchx
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Mgozer Posted at 3-19 00:44
It looks to me that this issue is wide spread and there is no Mavic Mini not affected. It is as per specification.
Sometimes it is noticeable, sometimes not, it only depends on the shot.
The last one posted here is very visible.

Actually I'm not sure every Mavic Mini has this problem - in MilesDeep videos (YouTube), the horizon looks perfect at the edges of the frame (also in phone screen recordings - definitely not adjusted in post-processing).
2020-3-19
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Mgozer
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I just gave a look at his videos and I cannot see any distortion.
It have to be said that it would take some specific tests to really say that (taking a picture of a geometric pattern, for example), but from his videos, it seems all ok.
2020-3-19
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