ruby on rails - Heroku imagemagick brightness parameter -

when trying change brightness of image (paperclip post processing) @ heroku via imagemagick following code:

command = "#{file.expand_path(@file.path)} -resize x300^ -brightness-contrast +50 -gravity center -crop 300x300+0+0 -colorspace gray #{file.expand_path(dst.path)}" 

i have following error:

convert: unrecognized option `-brightness' @ error/convert.c/convertimagecommand/844. 

how can change brightness of image?