Workflow for Structured Light capture

[Jonathan Hung]

Hi Zeshan,

As with stereo capture, I hope to start talking about structured light capture for the end user. I will start by writing what I understand of the process, and you can help correct and elaborate as needed.

1. Mount projector adjacent to camera

2. Calibrate

- project pattern onto base surface and take a picture - this becomes the baseline image.

3. Capture

- book is placed in front of projector / camera

- projector is turned on, pattern is projected onto book surface

- image 1 is captured.

- projector is turned off

- image 2 is captured.

- repeat for each page.

4. Dewarp

- input: baseline image, and image pair

- output: dewarped rendition of the book surface

Questions:

- In some cases a user may mount the projector causing lines to not be uniform. Does this matter?

- Does the projector and camera have to be perpendicular to the book surface?

Thanks Zeshan.

- Jon.

[Muhammad Zeshan Afzal]

Hi Jon

Following are the steps for SL capture-dewarp and their
brief description and answer to the questions

1. Mount projector adjacent to camera

In the current setup projector is mounted right above the camera.
The benefit is to this approach is that we would be able to avoid
any distortions if the camera and projector center are aligned.
------------------------------------

2. Calibrate

- project pattern onto base surface and take a picture - this becomes
the baseline image.

This is still under consideration. The idea is that we should be
able to work without any calibration.
Current experiments are without any calibration.
Lets hope that this works otherwise the procedure is very
complicated and it involves projecting by projector and
capturing by camera and then doing a calibration. It is not the part
of opencv. It might require to embed some open source
after looking at the license information.
---------------------------

3. Capture

- book is placed in front of projector / camera
- projector is turned on, pattern is projected onto book surface
- image 1 is captured.
- projector is turned off
- image 2 is captured.
- repeat for each page.

The capture procedure is as follows
- First the pattern is projected over the flat surface to get a reference image.
(This image is captured only once as long as the position of the
setup remains fixed)
Following are repeated for each page
- The book is placed under the camera and projector and image is
captured with pattern.
- We use projector as a light source for capturing the book image for
texture mapping.
Projector illuminates the book for capturing and we take the image.
It works with books with normal pages. The books with reflecting
pages pose difficulties.


---------------------------------------------

4. Dewarp
- input: baseline image, and image pair
- output: dewarped rendition of the book surface

- base image, pattern image, image for texturing

----------------------------------------------

Questions:
- In some cases a user may mount the projector causing lines to not be
uniform. Does this matter?

It will be very desirable that the camera and projector centers are aligned.
For other cases the work is under progress but not yet finished.
Considering the deadline for release it might be included in the
next version.

- Does the projector and camera have to be perpendicular to the book surface?

It would make the capture and further processing a lot easier with
better calibration results.
-----------------------------------------------


Cheers

Shan

[E^3]

Hi Mr Shan,

Good Day.

May I know the CVS / source code of the dewarping method?

Thanks

E^3

[Muhammad Zeshan Afzal]

Hi E^3
The work is still in progress. We will announce it on the
mailing list as soon as it is available for public.

Best Regards

Shan