As said here Cannot start GenICamBrowser - libpng missing, I needed to add a few env vars to the .xsessionrc file :
CVB=/opt/cvb
GENICAM_GENTL64_PATH=/opt/cvb/drivers/genicam
CVGENICAM_REGISTRY=/var/opt/cvb/Registry
GENICAM_CACHE_V3_0=/var/opt/cvb/genicam
CVBDATA=/var/opt/cvb
CVBCONFIG=/etc/opt/cvb