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Calibration Questions Re Frame Rate | Scale -30 mm

The place for questions, problems, comments and tips regarding the camera calibration.

Calibration Questions Re Frame Rate | Scale -30 mm

Postby WP2016 » Tue Jun 21, 2016 3:33 am

Hello, all,

I upgraded my cameras to achieve a faster fps (from 4.6 to 25).

Before the upgrade, I have successfully calibrated the system for a 30mm scale size. However, after I updated the camera, I cannot achieve a successful calibration regardless how I change the position and orientation of the camera and projector.

I notice some difference in the screen for some flickering of the images. I am not sure if that matters at all. I have searched and found a couple threads on calibration for small scale and I referenced one of the setups (which helped with my initial successful setup).

My question is: should I worry about the camera setup (i.e., fps, shutter speed, etc.) at all when I am calibrating? I think not - I thought what only matters was the relative angles between the two. However, is it possible that the projector cannot follow the fps of the camera so the data wasn't synchronized properly for calibration? I just want to rule out some possibilities if anyone knows.

Thanks in advance!

Current hardware:

Projector: Acer K132 + 10X closeup lens
Camera: Grasshopper 3 GS3-U3-28S4C-C @ 34ms exposure time
Computer: USB 3.0, 2.6 GHz, GPU: 3G NVidia 970M, 32G RAM.
Calibration scale: 30 mm, about 10 cm to projector.
Attachments
2016-06-20_21-16-25.png
Projector: Acer K132 + 1/2/4/10 X closeup dai. 52 mm.
Camera: Grasshopper 3 GS3-U3-28S4C-C (@ 1600 X 1200, 30 fps); Lens: 8-50 mm F/1.4.
Computer: USB 3.0, CPU: 2.6-3.5 GHz, GPU: 3G NVidia 970M, 32G RAM.
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WP2016
 
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Location: TX, USA

Re: Calibration Questions Re Frame Rate | Scale -30 mm

Postby drndadoo » Tue Jun 21, 2016 9:34 am

Hi WP2016,

when you calibrate the system, do you get any error message?
If you get flickering signal, check your exposure settings, set it on 1/60 then your cam and projector will be synced.
drndadoo
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Re: Calibration Questions Re Frame Rate | Scale -30 mm

Postby WP2016 » Wed Jun 22, 2016 12:38 am

Hi, drndadoo,

Yes, the system said it couldn't map the projector and calibration failed. But now I unexpectedly solved the issue.

I change the camera resolution and the calibration worked... I changed from 1928 x 1448 to 1600 x 1200, then the calibration was successful (frame rate changed from 26 to 30). I also noticed the flickering gone... The shutter speed was constant at 32 ms.

One more note: at the 1928 resolution, the texturing shows a gradual variation of color - not white or grey at all. But after changing to the 1600 resolution, the white balance worked by itself.

I have no explanation on what's going on. But now I can scan. Any comment is still welcome.

Cheers.
Attachments
Forumfollowup.jpg
Projector: Acer K132 + 1/2/4/10 X closeup dai. 52 mm.
Camera: Grasshopper 3 GS3-U3-28S4C-C (@ 1600 X 1200, 30 fps); Lens: 8-50 mm F/1.4.
Computer: USB 3.0, CPU: 2.6-3.5 GHz, GPU: 3G NVidia 970M, 32G RAM.
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WP2016
 
Posts: 13
Joined: Mon Jan 25, 2016 11:54 pm
Location: TX, USA

Re: Calibration Questions Re Frame Rate | Scale -30 mm

Postby avogra » Wed Jun 22, 2016 7:37 am

your camera shutter has to be in sync with the projector. usually the projector runs at 60Hz, so your camera shutter should be set to 1/60s or 1/30s or 1/20. this way it will record 1 or 2 or 3 complete frames from the projector. This is because DLP beamers do brightness by turning micro mirrors on for shorter (dark) or longer (bright) during one frame. to make color, they do this first for red, then for green and then for blue, all that during 1/60 s. if you set your shutter to e.g. 1/50s, you might get one full frame and additionally some of the red pixels from the next frame, resulting in those colorbars wandering over the preview image.
avogra
 
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