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Author Topic: Lens corrections in Camera RAW good or not?  (Read 2442 times)

maveo

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Lens corrections in Camera RAW good or not?
« on: April 06, 2016, 12:22:41 PM »
Hi,

i was wondering if it makes sense to correct lens distortion and vignette in Camera Raw before loading the images into Photoscan. What are ure expieriences? Thank you very much.

Dom

JMR

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Re: Lens corrections in Camera RAW good or not?
« Reply #1 on: April 06, 2016, 01:41:36 PM »
To my understanding it is not recomended.
Alignment in Photoscan includes external parameters estimation for cameras along with sensor/lens modeling.
So what's de need of doing lens corrections outide in advance?.
Many lens correction utilities are using simple math models for lenses, neglecting principal point decentering and tangential distortions. The photogrammetric corrections are referred to the principal point which is the point of best symetry in the the distortion distribution across the frame. If your photos have already been corrected under a simple lens model asumption, it might become uncertain the estimation of this center to which is referred the lens parameterization that Photoscan will apply.
That said, I suppose the answer would have been its just fine, if the lens corrections to be applied in advance have been calculated by a highly accurate photogrammetric approach and the zero distortion lens model is set as fixed prior to alignment.
It would be nice to read Alexey's veredict on the matter.

yoli

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Re: Lens corrections in Camera RAW good or not?
« Reply #2 on: March 08, 2018, 02:08:50 PM »
Bringing this topic up as I have the same interrogation.
I am using DxO PhotoLab (formerly DxO Optics) to pre-process the images, should I enable lens distortion correction ?
In my testings, enabling lens distortion correction didn't cause any problem for PhotoScan, but I would like a confirmation, maybe Alexey ? Thanks!

Kiesel

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Re: Lens corrections in Camera RAW good or not?
« Reply #3 on: March 08, 2018, 11:35:00 PM »
The user manual say at page 10:

"Modifications of photographs

PhotoScan can process only unmodified photos as they were taken by a digital photo camera.
Processing the photos which were manually cropped or geometrically warped is likely to fail or to produce highly inaccurate results. Photometric modifications do not affect reconstruction results."

yoli

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Re: Lens corrections in Camera RAW good or not?
« Reply #4 on: March 09, 2018, 10:44:41 AM »
Ok, so based on this, lens distortion correction, as long as done properly, should not impact reconstruction, this is my understanding.

Erik Holmlund

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Re: Lens corrections in Camera RAW good or not?
« Reply #5 on: March 09, 2018, 12:30:42 PM »
Hi,
The camera calibration needs to be very exact in order to not adversely affect the results. I can't remember where I've read it, but even thermal expansion on the sensor changes its characteristics. I also assume that mounting/unmounting a lens might shift e.g. the principal point by a tiny amount.

A kind of preprocessing can be done in PhotoScan, by just saving a camera calibration that you're certain in, but academia generally recommends against that.