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Author Topic: Lens Calibration : How to improve estimation?  (Read 6244 times)

jungeun

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Lens Calibration : How to improve estimation?
« on: January 26, 2023, 12:54:41 PM »
Dear.

I am using lens calibration for more accurate calibration than marker-based camera calibration.
I followed the tutorial below.
https://agisoft.freshdesk.com/support/solutions/articles/31000160059-lens-calibration-using-chessboard-pattern-in-metashape

Unfortunately, the reprojection error looks pretty big as shown in the attached picture, and I have no idea to how to improve this.

Here are my settings I used for :
- Camera used: Sony Corporation DSC-RX0M2
- Optimize f, Cx, Cy, K1~K3, P1, P2 with 100 images
- Since the monitor is quite small, the camera is placed 30 to 50 cm away from the monitor.
- To obtain 100 images, take a VIDEO first and get the frame with opencv. (exif information is lost)

So, I have two questions.

1. Is there any way to make better reprojection error?

2. I don't know if Lens Calibration is really better than marker-based camera calibration (which seems to uses exif data).
    Can the reprojection error be checked using the parameters obtained from marker-based camera calibration?
    How do I check which one is better?

You will be of great help. Thank you so much.
I spend so many time to here. Please help me  :'( :'( :'(
« Last Edit: January 30, 2023, 04:26:01 AM by jungeun »

tazzo

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Re: Lens Calibration : How to improve estimation?
« Reply #1 on: February 01, 2023, 10:07:25 PM »
Hello, images are very blurred.. if you manage to focus the screen would be better for sure.

jungeun

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Re: Lens Calibration : How to improve estimation?
« Reply #2 on: February 02, 2023, 05:01:43 AM »
Thank you tazzo! I totally agree with you.

However, the blur is caused by Focus and I'm not sure could I change it during only calibration.

As a rule of tumb, [Metashape LensCalibration] works well only if the chessboard occupies the entire image and my monitor is quite small.
So I put the camera quite close from the monitor, and calibration image becomes blurry since the camera was set based on shooting distance object.

Do you think change Focus option for calibration is OK?
What can I do? I have no idea..

Thank you so much for your help.
« Last Edit: February 02, 2023, 05:09:33 AM by jungeun »

tazzo

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Re: Lens Calibration : How to improve estimation?
« Reply #3 on: February 02, 2023, 04:33:30 PM »
Yes, a sharp checkboard image is essential. It's important to cover all the image sensor because worst imperfection are always at the corner of the lens.
Better to change the focus (you need to do this only once) than having completely blurred calibration pictures. You can use this calibration as (initial) starting point and allow Metashape to refine it during the alignment process.
Can you print the checkboard on an A4/A3 paper sheet? Then fix the sheet on a rigid surface. This may solve the problem.
« Last Edit: February 02, 2023, 04:36:12 PM by tazzo »