By the way, you can always use the Scripting Editor in MRIcroGL as a kind of command line, entering one or more commands at a time. Consider paste this script into the scripting editor and choose Control-R to run the command: You can now add one or more commands to change the image (e.g. new instructions are applied to the exisiting state machine). So you could run the command: And it will change image intensity without any other effects. You can add effects one at a time. The one special command is gl.resetdefaults(), which sets many settings back to their default settings. You only want to use this at the very start of a script to ensure that all scripts start with in a common state.