Photo3D Lab Info

This page contains relevant information about the photo3D lab usage.

Calibration Procedure

This describes the overall procedure for acquiring good calibration images. The command lines to execute are displayed in bold face (centered). Read the whole description before starting working in the lab. I want to put the focus on the fact that the equipement in the lab is very expensive, so take good care of it.

Getting Started

Log on photo3d (remote access: photo3d.vision.caltech.edu).

Start the X environment:

startx

Put your object on the scan table, and position the camera in order to have a good coverage of it.

Adjust camera focus and aperture.

Acquire one test image of the object (before calibration):

acquire test_image.ras

Check the image (focus and contrast) using your favorite image editing tool. Two alternatives:

xv test_image.ras display test_image.ras

Camera Calibration

Put up the calibration pattern (transparent checker board on the inclined plane), and acquire the camera calibration image:

acquire camera_calib.ras

Check for focus and calibration again.

Run camera calibration on the image, and do not touch any more either the camera or the calibration plane.

Projector Calibration

Take the transparent checker board pattern off the calibration plane (without moving the plane).

Turn on the projector lamp, and switch the monitor to the low resolution mode:

Ctr_Alt_+

Note that repeating that command would switch it back to its default mode (high resolution mode).

Adjust the focus of the projector, and use the aperture device to have the projected image focused over the entire calibration plane (it should already be on the lens - make sure it is well positioned). It is a good time to ajust the position of the projector thinking that in place of the calibration plane will be sitting your object.

Put up the projector calibration grid on the screen background with a reference point (called projector reference point):

calibra 16 16 256 240

Make sure that a "large" portion of the grid (including the reference point) is visible from the camera (preferably the reference point should be roughly located in the middle of the image, within the visible portion of the grid). If necessary, move the projector, and adjust the mirror angle.

Move the mouse cursor to the top left corner of the screen to that the the origin of the grid corresponds to the origin of the projector image. Acquire the projector calibration image:

acquire proj_calib.ras

Check for image contrast (there is a brightness control on the projector that you may want to play with).

Turn off the projector lamp using the remote control (bulbs are expensive, we don't have an infinite supply).

Run the projector calibration. From now on, you cannot touch/move/... either the camera or the projector.

From now on, you cannot touch/move/... either the camera or the projector. However, you can remove the calibration plane, and replace it by your object.

Acquiring stripe images

This describes the procedure to quickly acquire images of your object with stripes projected onto it.

Use the program stripe to acquire stripe images of your object. Example:

stripe my_object

This generates the set of pair of images my_object0_n.ras, my_object0_i.ras, my_object1_n.ras, my_object1_i.ras, ... my_object10_n.ras, my_object10_i.ras.

To know the pattern correspondence, you can ask (to it once only) to also save the stripe pattern images under the same format. To do so, use the same program stripe with an extra argument: the name of the pattern images:

stripe my_object pattern

This will, in addition to generating the object images, save the corresponding stripe pattern images under the raster files: pattern0_n.ras, pattern0_i.ras, pattern1_n.ras, pattern1_i.ras, ... pattern10_n.ras, pattern10_i.ras.

I advice you to do it only once to check for the stripe pattern configuration. You have to know that those patterns will always be the same from one acquisition to another.

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