Page 1 James M. Proper/Rod Heckaman

3D Imaging Using Coded Light

Camera Calibration

An attempt was made to determine the precision and accuracy of using camera nests for locating one camera in more than one position to gather multiple scene images.

Recall the Set-up:

Strappeddown barand solidsquare

Strapped downangle plate

Projector CameraPosition 1Position 2

Mounting table

Aerial View of Set-up

Object

Yes No

No

Yes

Accuracy(average)

Pre

cisi

on(r

epea

tabi

lity)

Yes No

No

Yes

Accuracy(average)

Pre

cisi

on(r

epea

tabi

lity)

Page 2 James M. Proper/Rod Heckaman

3D Imaging Using Coded Light

Camera Calibration

• Six circular targets were used on a flat vertical foam-board plate.

• X, Y and Z coordinates world were established by measuring the location of each target with respect to a fixed origin.

• Images were taken of the targets after repeatedly removing and replacing the camera from each nest.

• Ten images were taken at each camera location.

Image of circular targets

Page 3 James M. Proper/Rod Heckaman

3D Imaging Using Coded Light

Camera Calibration• Camera coordinates for each of the six targets were established through multiple

DIP steps.

o Histogramo Thresholdo Morphological location using erosion (center pixel found using a structuring

element the same size as the target)

Page 4 James M. Proper/Rod Heckaman

3D Imaging Using Coded Light

Camera Calibration• The average and standard deviation of the ten images was determined for each

target location.

Camera Position 1Trial/Target 1 2 3 4 5 6 7 8 9 10 Average Stdv.

x1 459 461 461 461 460 461 461 461 462 461 461 1y1 60 57 59 58 59 60 58 58 56 58 58 1

x2 249 249 249 249 249 249 249 249 249 249 249 0y2 62 60 61 60 61 62 61 61 59 60 61 1

x3 52 49 50 49 50 50 49 49 47 49 49 1y3 67 65 66 65 66 67 66 65 64 65 66 1

x4 51 48 49 49 50 49 49 49 47 49 49 1y4 279 280 280 280 280 281 280 280 280 280 280 0

x5 249 249 249 249 249 249 249 249 249 249 249 0y5 282 282 283 282 283 284 283 282 282 282 283 1

x6 460 462 462 462 462 462 462 462 463 462 462 1y6 284 285 285 285 285 286 285 285 285 285 285 0

Page 5 James M. Proper/Rod Heckaman

3D Imaging Using Coded Light

Camera Calibration

Camera Position 2Trial/Target 1 2 3 4 5 6 7 8 9 10 Average Stdv.

x1 451 449 453 450 451 452 452 452 452 456 452 2y1 63 64 61 62 62 62 62 62 62 59 62 1

x2 255 255 255 256 256 256 257 257 255 257 256 1y2 59 60 58 59 60 59 61 61 59 58 59 1

x3 48 50 44 48 46 46 46 46 47 42 46 2y3 62 63 59 59 60 60 60 60 61 57 60 2

x4 51 53 48 51 51 50 50 50 50 46 50 2y4 286 285 287 284 285 286 286 286 287 288 286 1

x5 260 259 259 259 259 259 259 259 259 259 259 0y5 279 278 280 277 279 279 279 279 280 281 279 1

x6 455 453 457 454 455 456 455 455 456 460 456 2y6 273 272 273 271 272 272 273 273 273 274 273 1

• The average and standard deviation of the ten images was determined for each target location.

Page 6 James M. Proper/Rod Heckaman

3D Imaging Using Coded Light

Camera Calibration

Conclusions• Morphological techniques may not be the best way to locate targets. As the image

becomes distorted, it becomes more difficult to create a structuring element that will locate the center.

• As the image becomes more distorted, the accuracy becomes worse. This may be strictly due to using the morphological technique.

• Nevertheless, sub-pixel accuracy may not be possible when moving the camera repeatedly to several different locations. Multiple cameras permanently mounted would be much better.

Page 7 James M. Proper/Rod Heckaman

3D Imaging Using Coded Light

Camera Calibration

Next Steps• Try using different targets such as checkerboard type and use corner detection to

determine accuracy.

• Try using multiple cameras and tripods. This will require calibration and coded light imaging all in one small time frame since it will probably not be practicle to keep the set-up in tact for long periods of time.