Dear Yong Peng,

It seems that I've been wrong, but I didn't understand what this passage
means in practice.
Now I have found a coherent explanation in Patisambhidamagga 2.38.
As I understand, the difference between following two 'releases'
(vimokkha) is that in the first case one gets appropriate recognition
(sa~n~naa) through internal perceptual image (nimitta), and in the
second case through external.

212. Katha.m ruupii ruupaani passatiiti– vimokkho? Idhekacco
ajjhatta.m paccatta.m niilanimitta.m manasikaroti, niilasa~n~na.m
pa.tilabhati. So ta.m nimitta.m suggahita.m karoti, suupadhaarita.m
upadhaareti, svaavatthita.m avatthaapeti. So ta.m nimitta.m suggahita.m
katvaa suupadhaarita.m upadhaaretvaa svaavatthita.m avatthaapetvaa
bahiddhaa niilanimitte citta.m upasa.mharati, niilasa~n~na.m
pa.tilabhati. So ta.m nimitta.m suggahita.m karoti, suupadhaarita.m
upadhaareti, svaavatthita.m avatthaapeti. So ta.m nimitta.m suggahita.m
katvaa upadhaaretvaa svaavatthita.m avatthaapetvaa aasevati bhaaveti
bahuliikaroti.
Tassa eva.m hoti– “ajjhatta~nca bahiddhaa ca ubhayamida.m ruupan”ti,
ruupasa~n~nii hoti. Idhekacco ajjhatta.m paccatta.m piitanimitta.m …pe…
lohitanimitta.m …pe… odaatanimitta.m manasikaroti, odaatasa~n~na.m
pa.tilabhati. So ta.m nimitta.m suggahita.m karoti, suupadhaarita.m
upadhaareti, svaavatthita.m avatthaapeti. So ta.m nimitta.m suggahita.m
katvaa suupadhaarita.m upadhaaretvaa svaavatthita.m avatthaapetvaa
bahiddhaa odaatanimitte citta.m upasa.mharati, odaatasa~n~na.m
pa.tilabhati. So ta.m nimitta.m suggahita.m karoti, suupadhaarita.m
upadhaareti, svaavatthita.m avatthaapeti. So ta.m nimitta.m suggahita.m
katvaa suupadhaarita.m upadhaaretvaa svaavatthita.m avatthaapetvaa
aasevati bhaaveti bahuliikaroti. Tassa eva.m hoti– “ajjhatta~nca
bahiddhaa ca ubhayamida.m ruupan”ti, ruupasa~n~nii hoti. Eva.m ruupii
ruupaani passatiiti– vimokkho.

Katha.m ajjhatta.m aruupasa~n~nii bahiddhaa ruupaani passatiiti–
vimokkho? Idhekacco ajjhatta.m paccatta.m niilanimitta.m na
manasikaroti, niilasa~n~na.m na pa.tilabhati; bahiddhaa niilanimitte
citta.m upasa.mharati, niilasa~n~na.m pa.tilabhati. So ta.m nimitta.m
suggahita.m karoti, suupadhaarita.m upadhaareti, svaavatthita.m
avatthaapeti. So ta.m nimitta.m suggahita.m katvaa suupadhaarita.m
upadhaaretvaa svaavatthita.m avatthaapetvaa aasevati bhaaveti
bahuliikaroti.
Tassa eva.m hoti– “ajjhatta.m aruupa.m, bahiddhaa ruupamidan”ti,
ruupasa~n~nii hoti. Idhekacco ajjhatta.m paccatta.m piitanimitta.m …pe…
lohitanimitta.m …pe… odaatanimitta.m na manasikaroti, odaatasa~n~na.m na
pa.tilabhati; bahiddhaa odaatanimitte citta.m upasa.mharati,
odaatasa~n~na.m pa.tilabhati. So ta.m nimitta.m suggahita.m karoti,
suupadhaarita.m upadhaareti, svaavatthita.m avatthaapeti. So ta.m
nimitta.m suggahita.m katvaa suupadhaarita.m upadhaaretvaa
svaavatthita.m avatthaapetvaa aasevati bhaaveti bahuliikaroti. Tassa
eva.m hoti– “ajjhatta.m aruupa.m bahiddhaa ruupamidan”ti,
ruupasa~n~nii hoti. Eva.m ajjhatta.m aruupasa~n~nii bahiddhaa ruupaani
passatiiti– vimokkho.

Metta, Dmytro