stereo vision problem

[marko_hocevar]

Dear Madams/Sirs,

I would like to setup a stereo vision system. Unfortunately calibration of the stereo cameras or reconstruction of depth image failed in my case and I do not know why.

I have used two Basler Ace cameras, mounted on a machined stand. They are rather well aligned, and distance between the two cameras is 100 mm. For calibration I used a wooden plate with a grid, mounted on a photo stand as seen on the picture below. Illumination was provided by seven powerful LEDs.

I used stereo vision.vi example, provided with Vision 2012 and followed recommendations from this thread (http://forums.ni.com/t5/Machine-Vision/Stereo-library-2012-pointers/m-p/2171812). I have reduced image resolution to 640x480 and pixel depth to 8 bit grayscale. All calibration dots are well recognized during the stereo calibration procedure. In the attached calibration images pan and tilt angles were around 22° and 45°. Calibration looks ok according to rotation, essential and fundamental matrices.

However, I do not get proper depth nor disparity image. Values of pixels in depth image are 1.#R. Perhaps I should set parameters, but I do not know how.

Attached are nine calibration image pairs and two sample image pairs.

I would be very happy if someone could help me to solve this problem.

With many best regards

Marko

[lizhuo_lin]

Dear marko_hocevar：

can you tell me the distance between two points in the grid and the dimension of pionts? 

[marko_hocevar]

Dear lizhuo_lin,

the distance among dots in the grid was in both directions 10 mm. There were 20 dots in both directions, so the size of entire grid was 190x190 mm. The grid used is the one provided by NI in the file CalibrationGrid.pdf.

This is also a question that I wanted to ask in my original post, but I forgot. How can calibration algorithm in Stereo Vision.vi know the actual distance to the grid and how is transformation to physical units (mm, m, in, ...) performed?

With many best regards

Marko

[lizhuo_lin]

Dear marko

I use stereo vision.llb which is  attached by LabVIEW, you can find it through help > find examples, I change some image name to use your image, but I can not get right depth image.

you can set spacing between dots and units in grid feature extraction> IMAQ Calibration Target to Points> Grid Descriptor.

Regards

lizhuo_lin