A double-injection field-effect transistor has an anode, a cathode, a substantially transparent channel, a substantially transparent gate insulator, and at least one substantially transparent gate electrode. In the operational position, the tape head mechanism is detachably held by a pin in operational alignment with a box flap closure apparatus. Air in the workspace is discharged to outside via filters. In another example, the RGB form is converted to the L*a*b* form and two extra L* components for use in sharpening a converted image. In this way, the jaw cannot be closed inadvertently and the locking element does not hamper the closure movement.