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Author Topic: image correction useful ?  (Read 5894 times)

Bruno Andrieu

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image correction useful ?
« on: October 25, 2014, 05:26:50 PM »
Hello Agisoft team
 
I use Nikon camera with standard nikon lenses (24mm or 35mm, fixed focal lenses) to take images.
Softwares as Nikon Capture or Dxomark allow correcting for lense distorsion. Would you recommend to use these corrections before using photos in Agisoft or rather work with the uncorrected images ?

Could you comment also for other options such as image sharpness improvment and noise reduction ?

Thanks

Bruno

nadar

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Re: image correction useful ?
« Reply #1 on: October 25, 2014, 10:48:39 PM »
I will suggest not changing anything to the geometry of captured images: photogrammetry is based on the analysis of the differences between images to determine 3D position. If you chanhe the geometry of the images, the analysis will be biased.

Correcting image distortion is certainly a bad idea. Sharpness enhancement modifies pixel value based on the value of neighbouring pixels. I don't know if this can have an incidence on photogrammetric process, but I will suggest to avoid it.

Removing vignetting, enhancing global contrast, changing colour balance doesn't chanhe the geometry of the image and hense should be allowed.

Of course modifying image geometry (rotation, perspective shift, and cropping) are prohibited.


mjankor@gmail.com

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Re: image correction useful ?
« Reply #2 on: October 26, 2014, 02:06:11 AM »
Which does bring up an interesting question of software based in camera correction - as used by a lot of newer cameras.

I haven't seen any sign of this being an issue though, having used M4/3s gear for panos, 360ยบ panos, and photoscan.

I agree with Nadar. Shadows and highlights adjustment, global exposure and contrast adjustment, etc should be fine (apply consistently to all images). I'd steer clear of anything like sharpening, cropping, straightening, etc.
« Last Edit: October 26, 2014, 02:08:44 AM by Martin.au »

Bruno Andrieu

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Re: image correction useful ?
« Reply #3 on: October 26, 2014, 01:55:59 PM »
Thanks for the answers.
My question was specifically about the use of software such as Dxomark, that do "professionnal  quality" image correction with output looking better  than when using  the software within the cameras.

When  you disable all camera software (eg on nikon 7000 or 5300) and do no correction at all, an enlarged image (eg 400%) show some defects (stringes, color noise, low FTM, etc).

I checked that for  "high iso" (> 400) and "medium quality" lenses, the 3D point clouds I obtained were much more dense when using with Dxomark corrected images than with  no correction at all.
However they are a lot of parameters in the software and my question is to clarify which corrections do really help and which should better be avoided (not speaking about image cropping, etc, which obviously is forbidden).

Bruno

Johny5566

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Re: image correction useful ?
« Reply #4 on: October 29, 2014, 09:15:27 AM »
I can't manage to align the images correctly although I have the GPS position for everyone of them. I haven't tried chunks because I've never worked with chunks before and I'm afraid the merging will not be as good as if I process everything in a single run, although I may be wrong. If anyone has had good experience with chunks please let me know.
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