The current github version of knitrBootstrap has a chunk option for the image thumbnail size with bootstrap.thumbnail.size
. They correspond to the bootstrap grid options, the default is col-md-6
.
The new version is not yet available on CRAN, but you can install it easily with devtools.
install.packages('devtools')
library(devtools)
install_github('jimhester/knitrBootstrap')
Please see the knitrBootstrap github page for full details on all the options and using the new version.