It looks like that the most convenient (and also perhaps only) way to achieve .brlcad (3d file) to .pix (picture) conversion would be to use the original BRL-CAD software. Unfortunately, we do not know about any other software capable of brlcad to pix conversion.
Convert BRL-CAD 3D file to Bitmap image.
We found one software available in the database for this conversion.
Multiplatform software - convert brlcad to pix on any platform
A CAD modeling tool
Convert from brlcad file format
The table with program actions contains information about what each program is capable of doing with their files. This may be a good pointer for further searches for certain file conversions and help you find the converter you are looking for if our search result is insufficient for you. However, it is far from perfect and may sometimes show results which are not really usable because of the nature of the software handles the files. So a conversion that appears as possible, just because of matched actions, may in fact not be possible.