The four subsets mentioned in the our paper correpond to the following light-source
directions (azimuth and elevation). Note that 45 images out of 64 were assigned to a subset.

Subset 1 -- angle<12 degrees from optical axis

'A+000E+00'; 'A-010E+00'; 'A+010E+00'; 'A-005E+10';
'A+005E+10'; 'A-005E-10'; 'A+005E-10'

Subset 2 -- 20<angle<25 degrees from optical axis

'A+000E-20'; 'A-010E-20'; 'A+020E-10'; 'A-025E+00';
'A-015E+20'; 'A-020E-10'; 'A+000E+20'; 'A+010E-20';
'A+020E+10'; 'A+025E+00'; 'A+015E+20'; 'A-020E+10'

Subset 3 -- 35<angle<50 degrees from optical axis

'A+000E-35'; 'A-035E+15'; 'A-035E-20'; 'A-020E-40';
'A-035E+40'; 'A-050E+00'; 'A+000E+45'; 'A+035E+15';
'A+035E-20'; 'A+020E-40'; 'A+035E+40'; 'A+050E+00'

Subset 4 -- 60<angle<77 degrees from optical axis

'A-050E-40'; 'A+060E-20'; 'A-060E-20'; 'A-035E+65';
'A-070E+00'; 'A-070E-35'; 'A-070E+45'; 'A+050E-40';
'A+060E+20'; 'A-060E+20'; 'A+035E+65'; 'A+070E+00';
'A+070E-35'; 'A+070E+45'