Команда convert -separate image1 image2, нет необходимости в дополнительных параметрах.
$ cat power_dpm_force_performance_level
auto
$ echo manual > power_dpm_force_performance_level
$ cat power_dpm_force_performance_level
manual
$ cat power_dpm_state
balanced
$ echo performance > power_dpm_state
$ cat power_dpm_state
performance
$ cat power_dpm_force_performance_level
auto
$ echo manual > power_dpm_force_performance_level
$ cat power_dpm_force_performance_level
manual
$ cat power_dpm_state
balanced
$ echo performance > power_dpm_state
$ cat power_dpm_state
performance