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StereoFlow - How to use

Javier Sánchez Pérez

Computer Science Department

University of Las Palmas de Gran Canaria


To execute the program write "StereoFlow[Color][Linux|SGI|SUN]" in the command line. 

It will appear a window (the XMW environment). In the "File" menu you have the possibility to create an image, load an image, save it, convert into another format,...

Inside the "Form Recog." menu you will find some applications for the problem of stereoscopic vision. These are:

Program What it does
Corner Detector An application to find the nearest corner to a selected point. To create a point select the "Edit -> Point -> Create" menu. This program is interesting for refining the points when using a calibrator to calibrate the cameras. It creates a file with the 2D points of the images which are later used to compute the camera projective matrix.
Projective Matrix An application to obtain the projection matrix of a camera. For this you need to know the actual 3D points of a calibration pattern and its correspondent 2D points on the images.
Fundamental Matriz An application to compute the Fundamental Matrix from two projection matrices (each one associated to the cameras of the stereo pair).
EpipolarTest An application to test the epipolar geometry given by the Fundamental Matrix (see section "How to use Epipolar Test" below).
Disparity Computation A program to compute the correspondences between the two images of the stereo pair (see below for a better explanation).
Reconstruction A program to make the final reconstruction. It generates a file with the 3D points of the scene (see below).

 There is also a program with this distribution called "VRML[Linux|SGI]" that converts a 3D file from the "Reconstruction" process into a Vrml file that can be visualized from a Vrml Browser like Cosmo Player.

 
How to convert files into XMW format

XMW works with four image formats. The first two formats (IMG and RIM) are XMW own formats (IMG-->integers, RIM-->floats). The other formats are TGA and RGB. If you want to utilize your own images, you will have to convert them into TGA or RGB (I think TGA is better). For this you have to use another program. XMWStereoZoom program only works with IMG format. The first think you have to do is to convert into this format. This can be done from the Convert submenu in the "File" menu. There you will find the four options.

Select the IMG option an press OK.

How to select an image in XMW

To select an image, you have to click on the image with the middle mouse button. Once you have setected it, its name appears on the XMW window. As you select other images, their names appear below. You may unselect an image by clicking again with the middle button on the image.

How to use StereoFlow

First, before carrying out the program, you have to select two images (see how to select an image: in the example, you have to select first Javier_Left.img and then Javier_Right.img). To execute our Program, you have to select the "Form Recog." menu. There you will  find three options:

    - Epipolar Test

    - Disparity computation

    - Reconstruction

 

The first one allows us to test if the system is well calibrated (see below), the second is the method to compute the disparity map and the third one is a little program to make reconstruction in 3D (see below). Select "Disparity computation". Then you will find 7 parameters: The first two parameters are used by our method.  The third one is the Fundamental Matrix (FMatrix.dat by default) which is a file containing the data of this matrix. The matrix is created in ASCII mode (take a look at the FMatrix.dat in the example to see how it is strutured). The following two parameters are input parameters which are optionals and allows us to specify an initial approximation to our method. The last two are the outputs (U and V matrices as explained before) which are created at the end of the process as ASCII files (take a look at UMatrix.dat in the example). The header of these files is the size (width height).

Then press OK.

How to use EpipolarTest

This is a program to graphically verify if the system is well calibrated. This program draws the epipolar lines on the right image for the selected points on the left. Select two images (Javier_Left and Javier_Right). Create a point on the left image. For this, you have to access to the "Point" submenu in the "Edit" menu and select "Create". Once you have selected "Create" if you click on the left image, it will appear a little cross indicating that the point is selected. Execute the submenu "EpipolarTest" in "Form Recog.". There are four parameters. Only the first and the last are used. The first one is to indicate for which point do you want to draw the epipolar line (you may select several points and in this box you select the point to draw: first=0, second=1, third=2, ...). The last parameter is the Fundamental Matrix file. [The two images must be visibles. If not it may appear some mistakes on the right image]

Then press OK.

How to use Reconstruction

It is also possible to reconstruct the 3D scene by using the U and V matrices and the P and P´ projection matrices. The output is an ASCII file containing the 3D points. The header of this file is the size of the matrix. The 3D points are inserted in a single column (with "x y z" components in each row).


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  last update 24/12/2004