If you are creating a new database file, it's necessary
to define a name with extension .tex (example: noname.tex). This
file will be used to keep all data. You can choose another file previously
created.
You have to give the dimensions of this database (if
it's new). These dimensions (samples and lines) define the size of images
and ROI's that will be used for classification.
Now, you can assemble your database.